Hygrothermal behavior of carbon fiber fabric reinforced vinylester resin composite structures

Hygrothermal behavior of carbon fiber fabric reinforced vinylester resin composite structures | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hygrothermal behavior of carbon fiber fabric reinforced vinylester resin composite structures Jincheng Gao, Xu Li, Jianhui Wei, Yuheng Zhang, Jihui Wang, Anxin Ding This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3623857/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Mar, 2024 Read the published version in Applied Composite Materials → Version 1 posted 8 You are reading this latest preprint version Abstract The hygrothermal aging of vinylester resin and its carbon fiber fabric reinforced composite structures are examined here, including moisture absorption and the resulting degradation of mechanical properties. The prepared resin casting and CFRP specimens were immersed into the deionized water and artificial seawater, respectively, at a temperature of 70°C, and weighed regularly along with the observation of surface morphologies using SEM and identification of variations in functional groups using FTIR spectrometer. Meanwhile, the mechanical properties of resin and CFRP were checked periodically. The results from gravimetric analysis show that resin immersed in deionized water behaves in non-Fickian diffusion due to strong hydrolysis, while CFRP obeys approximately the Fickian diffusion because of the embedded carbon fiber inhibiting the hydrolysis. The examination of mechanical properties for CFRP reveals that the interlaminar shear strength is influenced by the moisture absorption, with a maximum reduction of 13.5%. CFRP Vinylester resin Moisture absorption Aging Mechanical properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction Due to high stiffness/strength to weight ratio, carbon fiber reinforced polymer (CFRP) has been widely used for weight-sensitive equipment in many modern industries in recent decades, including aerospace and marine structures. For marine structures that are not relatively concerned with weight, the excellent durability of composites in marine environment is attractive. With the application of composite materials on the primary load-bearing components with large dimensions in marine structures, high stiffness is necessitated and CFRP is the preferred material for such applicationsLong-term exposure to the hygrothermal environment, polymeric matrix composites will inevitably undergo a certain aging process, deteriorating material properties and inducing potential threats to structural safety [ 1 – 8 ] . Especially, CFRP in structures that serve under marine environment may be seriously affected. Accurately evaluating the effects of long-term environmental exposure on the degradation of mechanical properties and understanding the aging mechanism are necessitated for durability design of composite components. Currently, the emphases of most studies regarding the hygroscopic behavior of composites are placed on the investigation on the moisture uptake as well as the exploration on the change in mechanical properties after aging. Commonly, moisture uptake is closely linked to the materials characteristics and environmental factors. Polymers are roughly classified as thermoset like polyester, vinylester and epoxy [ 9 – 11 ] and thermoplastic like polyethylene [ 12 ] . A large number of published papers [ 2 , 13 – 17 ] relating to the water uptake of resin and composites indicate that diffusion-controlled water uptakes obey Fickian diffusion model where the mass increases linearly and rapidly with the time at the initial period, and then slows down progressively until reaching a saturation value of equilibrium of water absorption. Consequently, based on Fickian law of diffusion, establishing the function of water uptake over time is the most common approach to describe the ingress of water into materials [ 18 ] . The water adsorbed into the polymers can be divided into the free water occupying free volume and bound water connected with the polymer molecular chain through hydrogen bonds. Zhou and Lucas [ 19 ] concluded that there are two types of bonding between water and resin, namely Type I and Type II bonding. Type I bound water is combined with the resin molecular chain by a single hydrogen bond, and has a low activation energy. Type II bound water relates to the polymer molecular chain by multiple hydrogen bonds with the resin and has higher activation energy. Type I bound water weakens the van der Waals forces between the polymer molecular chains, resulting in an increase in the mobility of the segments. While, Type II bound water forms bridges between the segments, resulting in secondary crosslinks. The content of type II bound water depends on the ambient temperature and aging time. Higher ambient temperature and longer exposure time lead to the massive formation of type II bound water [ 20 ] . In addition, non-Fickian absorption phenomena like dual-stage and pseudo Fickian diffusion [ 21 , 22 ] are frequently reported for the specific type of composites or polymers in hygrothermal environment. For example, the moisture absorption of reactive polymers with hydrolysable groups is driven by hydrolysis and can be elucidated by the dual-stage or Langmuir model [ 21 , 22 ] . Unlike pure resin, the transport of water into composites is more complex due to the fiber embedment, which disturbs the moisture diffusion within resin network perpendicular to fiber direction. For the effect of fiber on the water transport along the fiber direction, previous study [ 14 ] reveals that hygrothermal environment causes the damage to the carbon fiber-resin interface, which may allow capillary flow of moisture in the composites and finally aggravate the deterioration of materials. Whereas another study [ 23 ] reports that the carbon fiber induces the decrease of moisture absorption in CFRP as results of less number of voids and inertness of carbon fiber. Considering the significant distinctions in the molecular structure and hydrophilicity, the moisture uptake differs considerably between the dissimilar groups of polymers [ 24 , 25 ] .Polyester resin prevails in marine composite due to their low cost and ease of use but is prone to environmental degradation. Vinylester resin as a higher resistance to harsh chemical and environment than regular unsaturated polyester is increasingly selected in a variety of applications requiring increased strength over polyester resins. The engineers in composite filed are more focused on the deterioration of mechanical properties after water penetration into composites, therefore, obtaining the validated and comprehensive data on the loss of mechanical properties from water absorption is more of engineering significance. The relationship between moisture absorption and deterioration of material properties has been broadly examined and explanations of related mechanisms are relatively matured for resin. Commonly, the plasticization and swelling stress are some of the consequences of moisture penetration for non-reactive polymer without hydrolysable groups, lowering physical properties like glass transition temperature and mechanical properties. For reactive polymer with hydrolysable groups, loss in mechanical properties is induced by the voids or micro-cracks triggered by hydrolysis reaction. Because of anisotropicity of mechanical properties for composites, it is relatively more complicated to comprehensively estimate the decline of mechanical properties in the attack of moisture. In view of carbon fiber stability, the resin-dominated transversely tensile properties of composites or interfacial properties between fiber and resin degrade primarily in humid atmosphere [ 26 ] . As stated before, CFRP are light weight, high-strength/stiffness and excellent corrosion-resistant materials that have been utilized as an alternative material in marine equipment. Due to the lower moisture absorption and higher performance for vinylester resin than polyester resin, carbon fiber in combined with vinylester resin is the preferred choice for marine composite structures. Unfortunately, few studies report the hygroscopic behavior of carbon fiber reinforced vinylester resin. In this paper, the hygroscopic behavior of typical carbon fiber fabric reinforced vinylester resin composites (called as CFRP below) which were utilized in marine structures was carried out. Base on the service environment, the pure resin and CFRP specimens were manufactured and then immersed into two artificial accelerated aging conditions: artificial seawater and deionized water at a temperature of 70°C for 2160 hours. The weight change and surface micro-morphologies of CFRP and pure resin specimens were examined, in combination with detecting the variations of resin molecular chain functional groups to identify the process of mechanism of water penetration. Subsequently, the effects of hygrothermal aging on the mechanical properties of resin and composites were explored. The highlights of this paper are found in the more comprehensive research of mechanical properties in a longer aging time combined with microscopic characterization methods, the synchronous study of pure resin provides a better understanding of the hygroscopic behavior and aging mechanism of composites. 2. Materials and experiment 2.1 Experimental flowchart The flowchart for experimentally investigating the hygrothermal behavior of resin casting and CFRP is illustrated in Fig. 1 schematically, including manufacturing laminated plates, preparing standard specimens and setting aging conditions as well as properties, structural and morphological characterization of resin and CFRP. 2.2 Materials The constituent materials of CFRP are respectively 430LV vinylester resin from Nanjing Jinling DSM corporation and twill weave T300 carbon fiber fabric from Toray Industries. The curing agent is Aksu Butanox M50 and the accelerator is cobalt iso-octoate. 2.3 Specimen preparation Vacuum assisted resin infusion (VARI) process is employed to manufacture the CFRP laminated plates with dimensions of 500 mm ×500 mm ×4 mm (Length × Width × Thickness). After the resin was injected into the preform fabricated with twill weave T300 carbon fiber fabric, the plate was left to cure at room temperature for 24 hours, followed by a post-cure at 100°C for 4 hours at vacuum drying chamber. The final fiber volume fraction of the laminated plates was 54.5%. According to the test standard, the manufactured CFRP plates were cut to prepare the test specimens (see Fig. 2 ). The casting of resin specimens followed the same curing condition with CFRP plates and corresponding configurations of pure resin specimens are also given in Fig. 2 . Note that the edge faces of resin and CFRP specimens were sealed by the room temperature curing polytetrafluoroethylene (PTFE) solution again the moisture diffusion from edge faces. To remove the moisture absorbed during manufacturing, all specimens were placed in a vacuum over maintaining uniform temperature of 50°C for 48 hours before aging experiment. Before recording the effective weight of unaged specimens, all specimens dried in a desiccator until they remain constant in weight. Seven specimens were prepared for each test condition and effective values following detection were documented. For tests of mechanical properties, 3 to 6 valid data are generally kept after the exclusion of unacceptable failure modes and anomalous data. 2.4 Hygroscopic environments The artificial seawater produced based on ASTM-1141 and deionized water at a temperature of 70°C were prescribed according to the service environment for composites in marine structure. Table 1 Aging environments and prescribed time intervals for experimental measurement Terms Hygroscopic environments Deionized water Artificial seawater Temperature 70°C Time intervals for weighing specimens 1/2/3/5/7/9/12/15/19/23/30/38/48/60/90/120 days (24/48/72/120/168/216/288/360/456/552/720/912/1152/1440/2160/2880 hours) Tensile properties of CFRP and pure resin 0/7/14/90 days(0/168/336/2160 hours) Compressive properties of CFRP and pure resin 0/7/14/90 days(0/168/336/2160 hours) In-plane shear properties of CFRP 0/7/14/90 days(0/168/336/2160 hours) Interlaminar shear strength of CFRP 0/7/14/90 days(0/168/336/2160 hours) 2.5 Characterization and testing 2.5.1 Moisture absorption behavior Weight measurement CFRP and resin specimens were weighed in compliance with ASTM D5229 and ASTM D570, respectively. The wet specimens were periodically withdrawn from the environmental tank based on the prescribed time intervals (see Table 1 ), and dried to exclude the surficial water before weighing. After weighing the samples, they were immediately returned to the prescribed medium. The weight change of specimens M t was recorded by $${M}_{t}=\left(\frac{{w}_{t}-{w}_{0}}{{w}_{0}}\right)\times 100\%$$ 1 where w t and w 0 are the mass of the specimens at time t and initial state. Note that the weight change of resin matrix in CFRP was also calculated by excluding the mass of carbon fiber using Eq. ( 1 ). One-dimensional diffusion is expressed as: $$\frac{\partial \text{C}}{\partial t}=D\frac{{\text{d}}^{2}C}{{\text{d}x}^{2}}$$ 2 where C and D are respectively the concentration and diffusion coefficients. The solution to Eq. ( 2 ) is commonly expressed as [ 18 ] : $${M}_{t}={M}_{\infty }\left\{1-\text{e}\text{x}\text{p}\left[-7.3{\left(\frac{Dt}{{b}^{2}}\right)}^{0.75}\right]\right\}$$ 3 M t and M ∞ are respectively the water uptakes by the material at t and equilibrium state. D can be calculated as: $$\text{D}={\pi }{\left(\frac{{M}_{t}h}{{4M}_{\infty }}\right)}^{2}\frac{1}{t}$$ 4 Scanning electron microscopy (SEM) Scanning electron microscope (JSM-IT300 from JEOL Ltd.) was used to observe the surface micro-morphologies of unaged and aged specimens. Fourier transform infrared spectroscopy (FTIR) The variation of resin molecular chain functional groups was characterized using the Fourier Transform Infrared Spectrometer (Nicolet 6700 from Thermo Electron Corporation). 2.5.2 Mechanical properties Tensile test Tensile properties of CRFP were tested according to ASTM D3039 using universal testing machine LE055 from Lishi (Shanghai) Instruments Ltd. with a load speed of 2mm/min. The configuration of specimens is depicted in Fig. 2 a where the glass fiber fabrics reinforced epoxy resin tabs are bonded to ends of the specimens using high elongation adhesive system. Tensile test of pure resin was in accordance with GB/T 2567. One strain gauge was bonded to on the surface of the specimens to measure tensile strain. Compressive test Compressive properties of CFRP were performed based on ASTM D6641 using LE055 with a load speed of 1.3mm/min. Two strain gauges were bonded to on the back and front surfaces of specimen to record tensile strain and monitor percent bending. Compressive test of pure resin was in accordance with GB/T 2567. In-plane shear test Shear properties of CFRP were performed in compliance with ASTM D7078 using LE055 with a load speed of 2 mm/min. Two 120-5AA gauges were bonded to on the surface of the specimens in an angle of 45° with fiber direction to calculate shear strain. Interlaminar shear strength test Interlaminar shear strength of CFRP was tested consistent with ASTM D2344 using LE055 with a load speed of 1 mm/min. Seven specimens were prepared per test condition and effective values after screening were preserved. Commonly, 3–6 valid data are retained after excluding the unacceptable failure modes and abnormal data. 3. Results and discussion 3.1 Weight change Figure 3 shows the evolution of surface morphologies over aging time for the pure resin immersed into deionized water and artificial seawater using SEM. The unsmooth appearance of unaged resin specimens with certain amounts of wrinkles in Fig. 3 a were observed due to the forming of residual stress in the casting process. After immersion for 168 hours in two harsh environments, the appearance has changed to be smooth because of the release of residual stress caused by the moisture diffusion into resin which was commonly accompanied by the generation of the swelling stress (see Fig. 3 b and Fig. 3 e). Subsequently, the circle-like superficial pits initiated on the smooth surface of resin specimens immersed in deionized water (see Fig. 3 c), but this phenomenon didn’t arise in those immersed in the artificial seawater (see Fig. 3 f). With the increase in immersion duration, the smaller pits grew greatly in appearance, even extensive voids emerged in the deep layers to form a pathway for the ingress of moisture after immersion for 2160 hours for the resin specimen in deionized water (see Fig. 3 d). The formation of pits and voids from SEM observation results demonstrates that the partial substances were lost during immersion period. Figure 4 illustrates the FTIR spectrums for pure resin immersed in deionized water and the characteristic peaks of used epoxy bisphenol vinyl resin before aging were labeled in Fig. 4 a. The spectrum displays a broad peak at 3454 cm − 1 that is related to the stretching vibration of hydroxyl (-OH) groups. As the immersion duration increased, the characteristic peak of hydroxyl groups gradually became broader and stronger in company with the movement to a lower wavenumber (see Fig. 4 b), revealing that the resin molecular chains were associated with water molecular in the form of hydrogen bonds to form bound water. It is because that the aggregation of water molecules and the formation of hydrogen bond not only increased the intensity of hydroxyl stretching vibration but also reduced the stretching vibration frequency. In addition, the peaks at 758 cm − 1 and 700 cm − 1 , which were associated with C-H out-of-plane bending vibration from benzene ring, disappeared after immersion in deionized water for 2160 hours (see Fig. 4 b). This could be explained by the fact that the pure resin underwent severe hydrolysis, and the hydrolysates were lost in the medium. Therefore, the change in surface morphologies for the resin immersed in deionized water was induced by the moisture uptake and hydrolysis. As a comparison, the crazing occurred and accumulated in the appearance of specimens with the prolongation of immersion in artificial seawater, which was due to the increase of swelling stress (see Fig. 3 f). And after immersion for 2160 hours, the crazing evolved to the small crakes and very tiny pits arose in the appearance (see Fig. 3 g), showing that hydrolysis also occurred at this stage but was of relatively weak intensity compared to the resin specimens immersed in deionized water during same immersion duration. Figure 5 depicts the development of surface morphologies of CFRP specimens immersed in deionized water and artificial seawater. Clearly, changes in morphology are invisible during the entire duration of the immersion. i.e. the hydrolysis in the resin matrix is weakened due to the embedment of carbon fiber which is hydrophobic and corrosion-resistant. Figure 6 gives the measured data for the change in weight of pure resin and CFRP specimens immersed under two prescribed humid conditions, together with the fitted curves. Considering the usage of PTFE to prevent moisture diffusion along the side faces, one-dimensional equation for Fickian diffusion using Eq. ( 3 ) was adopted to fit the measured values. The detailed parameters for fitted curves are tabulated in Table 2 . Resin specimens immersed in artificial seawater and deionized water behaved in the distinct trends of the moisture absorption (see Fig. 6 a). The former appeared to correspond to Fickian diffusion behavior, i.e. the curve of moisture absorption in initial stage was a linear function of square root of time, followed by an equilibrium saturation value of water uptake of 1.0% after the immersion of 2160 hours. But the weight slightly fluctuated in the final plateau phase of curve, departing from the characteristics of Fickian model to some extent. From previously published literature, the occurrence of hydrolysis affected the equilibrium mass uptake. From the SEM observation results in Fig. 3 g, we can know that relatively weak hydrolysis happened and resulting hydrolysis-controlled moisture absorption and mass loss brought about the deviation from the behavior of Fickian diffusion. Comparatively, the resin specimens immersed in deionized water appreciably followed the non-Fickian diffusion especially in the plateau phase (see Fig. 6 a). In initial stage of immersion, the weight change for resin immersed in deionized water also approximately linearly varied with square root of time, but subsequently fluctuated dramatically in the transition region, and finally the weight change kept relatively stable and slowly increased with the immersion time. Combined with SEM images in Figs. 3 a-d and FTIR spectrogram in Fig. 4 , it can be inferred that the dramatic wave of weigh in the initial plateau region resulted from the coupling of diffusion-controlled moisture absorption as well as hydrolysis-controlled moisture absorption and material loss. And the slight increase of weight in the last region of curve was dominated by hydrolysis-controlled moisture absorption. In contrast to resin specimens, CFRP specimens immersed into deionized water and artificial seawater nearly conformed to the Fickian diffusion with stable saturation level of 0.32% and 0.31%, respectively (see Table 2 ), and coefficients of diffusivity in the seawater was slightly larger than that in deionized water. Through Fig. 6 a, the water absorption of CFRP is significantly lower than pure resin. To clarify the role of carbon fiber on the water uptake of composites, the weight of carbon fiber is excluded for the calculation of weight change of CFRP in Eq. ( 1 ) and modified results are plotted in Fig. 6 b. The moisture absorption of resin matrix in CFRP is still lower than the pure resin in the same conditions, revealing that the carbon fiber inhibited the ingress of water into composites. Additionally, to differentiate the contribution of moisture uptakes and mass loss to weight change, the final masses of the pure resin and CFRP specimens immersed in deionized water were weighted after the aged specimens immersed in deionized water for 2160 hours were dried at 40°C for 800 hours (see Fig. 6 b). The final weight of the pure resin and CFRP specimens were reduced by 0.28% and 0.039% as compared to the unaged specimens. It reveals again that weight change of resin immersed into deionized water arose from the mass loss by hydrolysis as well as moisture uptake by diffusion and hydrolysis. And the hydrolysis could be neglectable for the CFRP specimens, i.e. weight change of CFRP was induced by the diffusion-controlled water uptake. Table 2 The non-linear fitted parameters for Fickian diffusion Items Effective equilibrium water uptake ( \({\varvec{M}}_{\varvec{\infty }})\) /% Diffusion coefficient ( D )/mm 2 •h − 1 Coefficient of determination ( R 2 ) Resin in deionized water 1.41 0.034 0.91 Resin in artificial seawater 1.10 0.047 0.97 CFRP in deionized water 0.32 0.016 0.99 CFRP in artificial seawater 0.31 0.027 0.98 CFRP in deionized water (excluding mass of fiber) 0.91 0.016 0.98 CFRP in artificial seawater (excluding mass of fiber) 0.88 0.047 0.97 3.2 Degradation of mechanical properties The fluctuation in tensile strength with immersion duration for pure resin and CFRP specimens is given in Fig. 7 . Meanwhile, the typical tensile stress-strain curves for unaged specimens and aged ones for 2160 hours in deionized water are provided in Fig. 8 . In accordance with the test standard, the tensile moduli of the resin and CFRP were calculated from the slope between the two points where their strain values are 0.001 and 0.003, respectively. The tensile strength of resin significantly decreased in the first experimental examination after immersion for 168 hours, with a 34.2% reduction from 46.7MPa to 30.7MPa and then maintained small waves in the remainder of deionized water immersion. And the same trend was observed for resin immersed in artificial seawater (see Fig. 7 a). Similarly, the modulus of aged resin declined significantly, as shown in Fig. 8 . It is well known that swelling stress due to moisture absorption is generally accompanied by the plasticization which reduces mechanical properties, and mass loss by hydrolysis also can also cause many local defects and lowers the mechanical properties. From SEM images in Fig. 3 and corresponding analyses, it can be inferred that degradation of resin properties in deionized water is jointly affected by hydrolysis and plasticization, and deterioration of resin properties in artificial seawater is mainly due to the plasticization. Figs.7b depicts the deterioration of tensile strength of CFRP specimens, and the typical tensile stress-strain curve is also added in Fig.8. Meanwhile, Fig.13a displays the typical and effective failure modes of CFRP tensile specimens with lateral and multi-modes failure types at the middle location of gauge area. Slightly different from the hygroscopic degradation of tensile properties for resin, there was the maximum reduction of 6.1% for the strength as compared to the virgin values for CFRP immersed in deionized water and artificial seawater, respectively. Moreover, the tensile modulus of aged composites was nearly equal to that of unaged composites. By comparing the stress-strain curves of the resin and the CFRP, it can be concluded that the fracture elongation of resin was larger than that of fiber, therefore the carbon fiber fractured before the matrix cracked during the damage of the composite. In short, the tensile properties of CFRP is not sensitive to deionized water and artificial seawater environment. It may be because of two reasons. One is that the tensile strength is mainly dominated by the carbon fiber whose properties can be regarded invariable during immersion duration, the other reason is that no obvious hydrolysis occurs in the resin matrix for CFRP specimens during immersion. Fig.9 displays the variations in compressive strength of pure resin and CFRP specimens with soaking duration, combined with typical failure modes of HAT, M(dh)GV where the measured data can be viewed as acceptable (Fig.13b). The typical stress-strain curves of resin and CFRP are also given in Fig.10. The strength of resin degraded inconsiderably in the vicinity of average value of 100 MPa with a fluctuation of ±2 MPa, showing that the absorbed moisture and mass loss have not influenced the compressive behavior of resin (see Fig.9a). By contrast, the compressive strength of CFRP declined markedly initially and then stabilized in the subsequent immersion duration. To be specific, the compressive strength fell a great deal in the first examination from 638 MPa to 559 MPa and kept a fluctuation of 20 MPa in the next examinations (see Fig.9b). The compressive modulus of the resin was computed based on the slope of curves in Fig. 10. The modulus of resin waved slightly after immersion for 2160 hours. Similarly, the compressive modulus of aged CFRP as the slope of stress-strain curve between two points (strains of 0.001 and 0.003) also degraded inconsiderably. It is well known that the compressive strength is mainly determined by the fiber buckling which is relevant with resin properties, fiber properties interfacial properties between fiber and resin as well as interlaminar properties between plies. The degradation of compressive strength of resin can be omitted from aforementioned experimental data plus the impermeability of carbon fiber to moisture, the drop in compressive strength of CFRP specimens was therefore due to the weakening of interfacial properties or interlaminar properties. To clarify the reason for the reduction of compressive strength of CFRP, the deterioration of interfacial and interlaminar properties was investigated below. The measured shear strength of CFRP is plotted in Figs. 11a, along with the typical and acceptable failure modes of shear test in Fig. 13 c. Horizontal cracking in gauge area between notches was encountered can be regarded as the valid failure mode. The shear strength in Fig. 11a was nearly constant during immersion in deionized water and artificial seawater. The stress-strain curve for in-plane shear test for CFRP is given in Fig. 12 . Likewise, the shear modulus as the slope between two points (strains of 0.002 and 0.006) also fell slightly. Shear modulus is mostly dominated by the resin properties, therefore the reduction in shear modulus can be viewed as the softening and increase in flexibility of resin matrix. Meanwhile, shear strength of CFRP can be deemed as an indicator of deterioration of interfacial properties between fiber and resin, and the stable shear strength of CFRP in Fig. 11a indicates a negligible degradation of interfacial properties. Figure 11b gives the interlaminar shear strength (ILSS) of CFRP specimens from short beam testing where the typical and effective failure modes of specimen are the delamination of layer in Fig. 13 d. Clearly, ILSS of specimens immersed in deionized water and artificial water respectively showed the reduction of 13.5% and 10.0% after immersion for 2160 hours from 67.9 MPa to 58.7 MPa and 59.6 MPa, showing the severe worsening of interlaminar properties. Observing the trend of material properties degradation with immersion time in Figs. 7 , 9 and 11, it is easily found that the reduction in properties for CFRP mainly occurred before two weeks’ immersion. The properties degradation is commonly caused by the moisture absorption and material loss. From previous analyses, it is known that the material loss can be negligible due to weak hydrolysis reaction for CFRP specimens. In combination with the results in Fig. 6 , i.e. the amount of water absorption for CFRP is a linear function of square root of time (t) and after about two weeks’ immersion, weight nearly keep stable. Therefore, the main properties degradation mainly occurs in the early stage of immersion. Meanwhile, noted that the measured data at some certain time exhibit big deviation from the average value, this is because that mechanical properties of composites show inherent deviation in the properties of constituent materials, especially for the fiber. Moreover, multiple failure modes which can be accepted based on the test standards further aggravate the deviation. Finally, the retention of strength for CFRP and resin specimens after immersion into deionized water and seawater for 2160 hours is summarized in Fig. 14 . From the ranking of reduction in magnitude, the tensile strength of pure resin specimens dropped most significantly, only with a retention of 64.5% of virgin value, and then the shear strength using short-beam tests for CFRP specimens retained 86.5% of virgin value. The other strength properties deteriorate inconsiderably with a retention of above 90%, even had a slight increase of 1% for compressive strength of resin. Meanwhile, the extent of degradation of the mechanical strength of CFRP and resin under deionized water and artificial water are nearly the same. 4. Conclusion The following conclusions can be obtained that: (1) SEM observation results in combination with FTIR images and curves of weigh change show that strong hydrolysis occurs for pure resin in deionized water. The resulting weight change with immersion duration behaves in non-Fickian diffusion, while the CFRP specimens approximately follows the Fickian diffusion due to the embedment of carbon fiber inhibiting the hydrolysis reaction. (2) The degradation of resin properties in deionized water is jointly affected by hydrolysis and plasticization, while the deterioration of resin properties in artificial seawater is mainly due to the plasticization. Meanwhile, the moisture diffusion into resin has a minor effect on the compressive behavior. (3) The properties degradation of CFRP specimens immersed in deionized water and artificial seawater is dominated by the diffusion-controlled moisture uptakes. Tensile and compressive properties deteriorate insignificantly, and main reductions occur in interlaminar shear strength for CFRP, with loss of 13.5% after 2160 hours’ immersion. Declarations Competing Interests：This study was funded by the Fundamental Research Funds for the Central Universities (WUT:203101002, 203201006) Data availability statement The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations. References W. Shao, Q. Sun, X. Xu, W. Yue, D. Shi, Durability life prediction and horizontal bearing characteristics of CFRP composite piles in marine environments, Construction and Building Materials 367 (2023) 130116. L. Liu, Z. Zhao, W. Chen, C. Shuang, G. 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Lolive, Characterization of sea water ageing effects on mechanical properties of carbon/epoxy composites for tidal turbine blades, Composites Part A: Applied Science and Manufacturing 78 (2015) 380-389. P. Sun, Y. Zhao, Y. Luo, L. Sun, Effect of temperature and cyclic hygrothermal aging on the interlaminar shear strength of carbon fiber/bismaleimide (BMI) composite, Materials & Design 32(8-9) (2011) 4341-4347. L.V. da Silva, E.A.W. de Menezes, J.R. Tarpani, S.C. Amico, Accelerated Ageing Effects on Short-Beam Strength Behavior of Pultruded CFRP Rods, Applied Composite Materials 29(2) (2022) 855-869. C.-H. Shen, G.S. Springer, Moisture Absorption and Desorption of Composite Materials, Journal of Composite Materials 10(1) (1975) 2-20. J. Zhou, J.P. Lucas, Hygrothermal effects of epoxy resin. Part I: the nature of water in epoxy, Polymer 40(20) (1999) 5505-5512. Y. Wang, W. Zhu, B. Wan, Z. Meng, B. Han, Hygrothermal ageing behavior and mechanism of carbon nanofibers modified flax fiber-reinforced epoxy laminates, Composites Part A: Applied Science and Manufacturing 140 (2021) 106142. H.G. Carter, K.G. Kibler, Langmuir-type model for anomalous moisture diffusion in composite resins, Journal of Composite Materials 12(2) (1978) 118-131. T. Peret, A. Clement, S. Freour, F. Jacquemin, Numerical transient hygro-elastic analyses of reinforced Fickian and non-Fickian polymers, Composite Structures 116 (2014) 395-403. D.K. Jesthi, R.K. Nayak, Evaluation of mechanical properties and morphology of seawater aged carbon and glass fiber reinforced polymer hybrid composites, Composites Part B: Engineering 174 (2019) 106980. R. Martin, Ageing of composites, Elsevier2008. P. Davies, Y.D. Rajapakse, Durability of composites in a marine environment, Springer2016. B.G. Kumar, R.P. Singh, T. Nakamura, Degradation of carbon fiber-reinforced epoxy composites by ultraviolet radiation and condensation, Journal of Composite materials 36(24) (2002) 2713-2733. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 12 Mar, 2024 Read the published version in Applied Composite Materials → Version 1 posted Editorial decision: Revision requested 04 Dec, 2023 Reviews received at journal 01 Dec, 2023 Reviewers agreed at journal 21 Nov, 2023 Reviewers agreed at journal 21 Nov, 2023 Reviewers invited by journal 21 Nov, 2023 Editor assigned by journal 20 Nov, 2023 Submission checks completed at journal 20 Nov, 2023 First submitted to journal 17 Nov, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3623857","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":251330237,"identity":"bad1b8ce-746a-4c38-b748-a06e3f06bde4","order_by":0,"name":"Jincheng Gao","email":"","orcid":"","institution":"Wuhan Second Ship Design and Research Institute","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jincheng","middleName":"","lastName":"Gao","suffix":""},{"id":251330238,"identity":"64268495-359e-4687-92eb-8a99cd54069b","order_by":1,"name":"Xu Li","email":"","orcid":"","institution":"Wuhan University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xu","middleName":"","lastName":"Li","suffix":""},{"id":251330239,"identity":"cb7dc33b-e464-48a0-951d-12c3dc6297b7","order_by":2,"name":"Jianhui Wei","email":"","orcid":"","institution":"Wuhan Second Ship Design and Research Institute","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jianhui","middleName":"","lastName":"Wei","suffix":""},{"id":251330240,"identity":"91c4f35d-a1fe-4cb8-a77e-31fed4bceac0","order_by":3,"name":"Yuheng Zhang","email":"","orcid":"","institution":"Wuhan University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuheng","middleName":"","lastName":"Zhang","suffix":""},{"id":251330241,"identity":"9c3ebf17-5df4-44b1-953f-d7ad3c3329d6","order_by":4,"name":"Jihui Wang","email":"","orcid":"","institution":"Wuhan University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jihui","middleName":"","lastName":"Wang","suffix":""},{"id":251330242,"identity":"83eb8542-c034-4cff-8b2f-098623689acd","order_by":5,"name":"Anxin Ding","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYHACgwMMDDYMBmA2G/Fa0oBamEnQAsSHSdDCPyN54+GCX+cTt0vkH2D4UHaYgX92A34tEmeOFRye2Xc7ceeMZAbGGecOM0jcOUDAmuM9Bod5e27nbriRzMDM2wZ0oUQCfh3yh3lAWs5BtPwlRosByBaeHwcgWhiJ0WII8gtvQ3L9hjOPDQ72nEvnkbhBQIvcjeTNn3n+2BkbHE98+OBHmbUc/wwCWsCAsQ1CHwBiHiLUg8AfItWNglEwCkbByAQACuhKBP/ySbcAAAAASUVORK5CYII=","orcid":"","institution":"Wuhan University of Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Anxin","middleName":"","lastName":"Ding","suffix":""}],"badges":[],"createdAt":"2023-11-17 05:29:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3623857/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3623857/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10443-024-10216-1","type":"published","date":"2024-03-12T09:12:09+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":46996611,"identity":"728844de-0046-4c2d-a568-1f6889c3fe89","added_by":"auto","created_at":"2023-11-23 22:43:30","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":281105,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart for investigating hygrothermal behavior of resin and CFRP\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/32ed58005dd4ed310052c485.png"},{"id":46995931,"identity":"06a7b34d-d36e-45f0-9214-ce5e8ff678db","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":226739,"visible":true,"origin":"","legend":"\u003cp\u003eStandard configurations for CFRP (\u003cem\u003ea\u003c/em\u003e, \u003cem\u003eb\u003c/em\u003e, \u003cem\u003ec\u003c/em\u003e, \u003cem\u003ed\u003c/em\u003e and \u003cem\u003ee\u003c/em\u003e) and resin (\u003cem\u003ef\u003c/em\u003e and \u003cem\u003eg\u003c/em\u003e) specimens\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/aa7088593100d48b892b1e4f.png"},{"id":46995933,"identity":"194e54b5-72fa-45d6-8776-30612d13a489","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":332805,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of surface morphologies using SEM for resin specimens immersed into deionized water and artificial seawater\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/f668a7a0a75917392978e155.png"},{"id":46995930,"identity":"b656aa02-0b71-4147-a1d7-10595ea9b838","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":26930,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectrogram for resin specimens immersed into deionized water\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/08c8c58bcff9321a14729551.png"},{"id":46997834,"identity":"51454a92-384f-43ce-8178-39c2d03885d8","added_by":"auto","created_at":"2023-11-23 22:51:30","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":356961,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of surface morphology using SEM for CFRP specimens immersed into deionized water and artificial seawater\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/95737b38aca99b7fd9c020ee.png"},{"id":46995932,"identity":"32c8cbf1-50d3-4df3-a0b7-625252f84795","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":35859,"visible":true,"origin":"","legend":"\u003cp\u003eCurves of weight change for resin and CFRP immersed in deionized water and artificial seawater\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/9f05f7d2a1f867bd0f271dfc.png"},{"id":46995936,"identity":"fe995fe7-17ab-47d6-9126-2d73873f92e3","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":36702,"visible":true,"origin":"","legend":"\u003cp\u003eTensile properties of resin and CFRP specimens during immersion\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/326be942c4fb835c88aac0df.png"},{"id":46995937,"identity":"409015cf-67c3-446d-bb74-7a61f6cc3ac3","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":30025,"visible":true,"origin":"","legend":"\u003cp\u003eTypical stress-strain curves of resin and CFRP under tensile load\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/593199a27fac95cf03ad9e48.png"},{"id":46996608,"identity":"63333090-e0f3-4e57-9ca1-791a1b1402e3","added_by":"auto","created_at":"2023-11-23 22:43:30","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":33169,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive properties of resin and CFRP specimens during immersion\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/e1bc40f5722c475fbcbbe8df.png"},{"id":46995934,"identity":"4788d58e-892f-473c-adb1-41001428eb10","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":36088,"visible":true,"origin":"","legend":"\u003cp\u003eTypical stress-strain curves of resin and CFRP under compressive load\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/991eb2d5d37445e31bd53012.png"},{"id":46997835,"identity":"1f83520f-d529-4877-98b9-d81e3191b642","added_by":"auto","created_at":"2023-11-23 22:51:30","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":30841,"visible":true,"origin":"","legend":"\u003cp\u003eIn-plane shear properties and interlaminar shear strength for CFRP specimens\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/4b49f4bf0e6a239624a35221.png"},{"id":46997836,"identity":"ebdd756d-6d61-413a-ad35-086b43975e86","added_by":"auto","created_at":"2023-11-23 22:51:30","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":26829,"visible":true,"origin":"","legend":"\u003cp\u003eTypical stress-strain curves of CFRP under in-plane shear load\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/426c69f52ee4b0b2cf449b12.png"},{"id":46995943,"identity":"776508eb-85b4-4515-96a3-b45ac2167453","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":677954,"visible":true,"origin":"","legend":"\u003cp\u003eTypical failure modes of CFRP under different loads (a) Tension, (b) compression, (c) in-plane shear and (d) short beam bending\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/01accac5d2610be7a683ea4c.png"},{"id":46995940,"identity":"a97b38d4-bd8b-44e3-a0cb-9071a45671ab","added_by":"auto","created_at":"2023-11-23 22:35:30","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":57655,"visible":true,"origin":"","legend":"\u003cp\u003eRetention ratio of strength of pure resin and CFRP after immersion for 2160 hours\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/62055e672b23cae3b6ab4649.png"},{"id":52745474,"identity":"8e2f0ed9-9b32-4edb-9037-92db85b98b31","added_by":"auto","created_at":"2024-03-15 09:12:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2346565,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3623857/v1/b0282690-04bc-484e-880e-ffd78ff11c40.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hygrothermal behavior of carbon fiber fabric reinforced vinylester resin composite structures","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDue to high stiffness/strength to weight ratio, carbon fiber reinforced polymer (CFRP) has been widely used for weight-sensitive equipment in many modern industries in recent decades, including aerospace and marine structures. For marine structures that are not relatively concerned with weight, the excellent durability of composites in marine environment is attractive. With the application of composite materials on the primary load-bearing components with large dimensions in marine structures, high stiffness is necessitated and CFRP is the preferred material for such applicationsLong-term exposure to the hygrothermal environment, polymeric matrix composites will inevitably undergo a certain aging process, deteriorating material properties and inducing potential threats to structural safety\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Especially, CFRP in structures that serve under marine environment may be seriously affected. Accurately evaluating the effects of long-term environmental exposure on the degradation of mechanical properties and understanding the aging mechanism are necessitated for durability design of composite components.\u003c/p\u003e \u003cp\u003eCurrently, the emphases of most studies regarding the hygroscopic behavior of composites are placed on the investigation on the moisture uptake as well as the exploration on the change in mechanical properties after aging. Commonly, moisture uptake is closely linked to the materials characteristics and environmental factors. Polymers are roughly classified as thermoset like polyester, vinylester and epoxy \u003csup\u003e[\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e and thermoplastic like polyethylene\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. A large number of published papers\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14 CR15 CR16\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e relating to the water uptake of resin and composites indicate that diffusion-controlled water uptakes obey Fickian diffusion model where the mass increases linearly and rapidly with the time at the initial period, and then slows down progressively until reaching a saturation value of equilibrium of water absorption. Consequently, based on Fickian law of diffusion, establishing the function of water uptake over time is the most common approach to describe the ingress of water into materials\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. The water adsorbed into the polymers can be divided into the free water occupying free volume and bound water connected with the polymer molecular chain through hydrogen bonds. Zhou and Lucas\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e concluded that there are two types of bonding between water and resin, namely Type I and Type II bonding. Type I bound water is combined with the resin molecular chain by a single hydrogen bond, and has a low activation energy. Type II bound water relates to the polymer molecular chain by multiple hydrogen bonds with the resin and has higher activation energy. Type I bound water weakens the van der Waals forces between the polymer molecular chains, resulting in an increase in the mobility of the segments. While, Type II bound water forms bridges between the segments, resulting in secondary crosslinks. The content of type II bound water depends on the ambient temperature and aging time. Higher ambient temperature and longer exposure time lead to the massive formation of type II bound water\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. In addition, non-Fickian absorption phenomena like dual-stage and pseudo Fickian diffusion \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e are frequently reported for the specific type of composites or polymers in hygrothermal environment. For example, the moisture absorption of reactive polymers with hydrolysable groups is driven by hydrolysis and can be elucidated by the dual-stage or Langmuir model \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eUnlike pure resin, the transport of water into composites is more complex due to the fiber embedment, which disturbs the moisture diffusion within resin network perpendicular to fiber direction. For the effect of fiber on the water transport along the fiber direction, previous study\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e reveals that hygrothermal environment causes the damage to the carbon fiber-resin interface, which may allow capillary flow of moisture in the composites and finally aggravate the deterioration of materials. Whereas another study\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e reports that the carbon fiber induces the decrease of moisture absorption in CFRP as results of less number of voids and inertness of carbon fiber. Considering the significant distinctions in the molecular structure and hydrophilicity, the moisture uptake differs considerably between the dissimilar groups of polymers\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e.Polyester resin prevails in marine composite due to their low cost and ease of use but is prone to environmental degradation. Vinylester resin as a higher resistance to harsh chemical and environment than regular unsaturated polyester is increasingly selected in a variety of applications requiring increased strength over polyester resins.\u003c/p\u003e \u003cp\u003eThe engineers in composite filed are more focused on the deterioration of mechanical properties after water penetration into composites, therefore, obtaining the validated and comprehensive data on the loss of mechanical properties from water absorption is more of engineering significance. The relationship between moisture absorption and deterioration of material properties has been broadly examined and explanations of related mechanisms are relatively matured for resin. Commonly, the plasticization and swelling stress are some of the consequences of moisture penetration for non-reactive polymer without hydrolysable groups, lowering physical properties like glass transition temperature and mechanical properties. For reactive polymer with hydrolysable groups, loss in mechanical properties is induced by the voids or micro-cracks triggered by hydrolysis reaction. Because of anisotropicity of mechanical properties for composites, it is relatively more complicated to comprehensively estimate the decline of mechanical properties in the attack of moisture. In view of carbon fiber stability, the resin-dominated transversely tensile properties of composites or interfacial properties between fiber and resin degrade primarily in humid atmosphere \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. As stated before, CFRP are light weight, high-strength/stiffness and excellent corrosion-resistant materials that have been utilized as an alternative material in marine equipment. Due to the lower moisture absorption and higher performance for vinylester resin than polyester resin, carbon fiber in combined with vinylester resin is the preferred choice for marine composite structures. Unfortunately, few studies report the hygroscopic behavior of carbon fiber reinforced vinylester resin.\u003c/p\u003e \u003cp\u003eIn this paper, the hygroscopic behavior of typical carbon fiber fabric reinforced vinylester resin composites (called as CFRP below) which were utilized in marine structures was carried out. Base on the service environment, the pure resin and CFRP specimens were manufactured and then immersed into two artificial accelerated aging conditions: artificial seawater and deionized water at a temperature of 70\u0026deg;C for 2160 hours. The weight change and surface micro-morphologies of CFRP and pure resin specimens were examined, in combination with detecting the variations of resin molecular chain functional groups to identify the process of mechanism of water penetration. Subsequently, the effects of hygrothermal aging on the mechanical properties of resin and composites were explored. The highlights of this paper are found in the more comprehensive research of mechanical properties in a longer aging time combined with microscopic characterization methods, the synchronous study of pure resin provides a better understanding of the hygroscopic behavior and aging mechanism of composites.\u003c/p\u003e"},{"header":"2. Materials and experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Experimental flowchart\u003c/h2\u003e \u003cp\u003eThe flowchart for experimentally investigating the hygrothermal behavior of resin casting and CFRP is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e schematically, including manufacturing laminated plates, preparing standard specimens and setting aging conditions as well as properties, structural and morphological characterization of resin and CFRP.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Materials\u003c/h2\u003e \u003cp\u003eThe constituent materials of CFRP are respectively 430LV vinylester resin from Nanjing Jinling DSM corporation and twill weave T300 carbon fiber fabric from Toray Industries. The curing agent is Aksu Butanox M50 and the accelerator is cobalt iso-octoate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Specimen preparation\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eVacuum assisted resin infusion (VARI) process is employed to manufacture the CFRP laminated plates with dimensions of 500\u003cem\u003emm\u003c/em\u003e \u0026times;500\u003cem\u003emm\u003c/em\u003e \u0026times;4\u003cem\u003emm\u003c/em\u003e (Length \u0026times; Width \u0026times; Thickness). After the resin was injected into the preform fabricated with twill weave T300 carbon fiber fabric, the plate was left to cure at room temperature for 24 hours, followed by a post-cure at 100\u0026deg;C for 4 hours at vacuum drying chamber. The final fiber volume fraction of the laminated plates was 54.5%. According to the test standard, the manufactured CFRP plates were cut to prepare the test specimens (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The casting of resin specimens followed the same curing condition with CFRP plates and corresponding configurations of pure resin specimens are also given in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Note that the edge faces of resin and CFRP specimens were sealed by the room temperature curing polytetrafluoroethylene (PTFE) solution again the moisture diffusion from edge faces. To remove the moisture absorbed during manufacturing, all specimens were placed in a vacuum over maintaining uniform temperature of 50\u0026deg;C for 48 hours before aging experiment. Before recording the effective weight of unaged specimens, all specimens dried in a desiccator until they remain constant in weight. Seven specimens were prepared for each test condition and effective values following detection were documented. For tests of mechanical properties, 3 to 6 valid data are generally kept after the exclusion of unacceptable failure modes and anomalous data.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Hygroscopic environments\u003c/h2\u003e \u003cp\u003eThe artificial seawater produced based on ASTM-1141 and deionized water at a temperature of 70\u0026deg;C were prescribed according to the service environment for composites in marine structure.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAging environments and prescribed time intervals for experimental measurement\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTerms\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eHygroscopic environments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDeionized water\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArtificial seawater\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e70\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime intervals for weighing specimens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e1/2/3/5/7/9/12/15/19/23/30/38/48/60/90/120 days\u003c/p\u003e \u003cp\u003e(24/48/72/120/168/216/288/360/456/552/720/912/1152/1440/2160/2880 hours)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTensile properties of CFRP and pure resin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e0/7/14/90 days(0/168/336/2160 hours)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompressive properties of CFRP and pure resin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e0/7/14/90 days(0/168/336/2160 hours)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIn-plane shear properties of CFRP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e0/7/14/90 days(0/168/336/2160 hours)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInterlaminar shear strength of CFRP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e0/7/14/90 days(0/168/336/2160 hours)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Characterization and testing\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.5.1 Moisture absorption behavior\u003c/h2\u003e \u003cp\u003e \u003cstrong\u003eWeight measurement\u003c/strong\u003e \u003cp\u003eCFRP and resin specimens were weighed in compliance with ASTM D5229 and ASTM D570, respectively. The wet specimens were periodically withdrawn from the environmental tank based on the prescribed time intervals (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), and dried to exclude the surficial water before weighing. After weighing the samples, they were immediately returned to the prescribed medium. The weight change of specimens \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e was recorded by\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${M}_{t}=\\left(\\frac{{w}_{t}-{w}_{0}}{{w}_{0}}\\right)\\times 100\\%$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewhere \u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e are the mass of the specimens at time \u003cem\u003et\u003c/em\u003e and initial state. Note that the weight change of resin matrix in CFRP was also calculated by excluding the mass of carbon fiber using Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). One-dimensional diffusion is expressed as:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\frac{\\partial \\text{C}}{\\partial t}=D\\frac{{\\text{d}}^{2}C}{{\\text{d}x}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eC\u003c/em\u003e and \u003cem\u003eD\u003c/em\u003e are respectively the concentration and diffusion coefficients. The solution to Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) is commonly expressed as\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${M}_{t}={M}_{\\infty }\\left\\{1-\\text{e}\\text{x}\\text{p}\\left[-7.3{\\left(\\frac{Dt}{{b}^{2}}\\right)}^{0.75}\\right]\\right\\}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cem\u003eM\u003c/em\u003e \u003csub\u003e \u003cem\u003et\u003c/em\u003e \u003c/sub\u003e and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026infin;\u003c/em\u003e\u003c/sub\u003e are respectively the water uptakes by the material at \u003cem\u003et\u003c/em\u003e and equilibrium state. \u003cem\u003eD\u003c/em\u003e can be calculated as:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\text{D}={\\pi }{\\left(\\frac{{M}_{t}h}{{4M}_{\\infty }}\\right)}^{2}\\frac{1}{t}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eScanning electron microscopy (SEM)\u003c/strong\u003e \u003cp\u003eScanning electron microscope (JSM-IT300 from JEOL Ltd.) was used to observe the surface micro-morphologies of unaged and aged specimens.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eFourier transform infrared spectroscopy (FTIR)\u003c/strong\u003e \u003cp\u003eThe variation of resin molecular chain functional groups was characterized using the Fourier Transform Infrared Spectrometer (Nicolet 6700 from Thermo Electron Corporation).\u003c/p\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.5.2 Mechanical properties\u003c/h2\u003e \u003cp\u003e \u003cstrong\u003eTensile test\u003c/strong\u003e \u003cp\u003eTensile properties of CRFP were tested according to ASTM D3039 using universal testing machine LE055 from Lishi (Shanghai) Instruments Ltd. with a load speed of 2mm/min. The configuration of specimens is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea where the glass fiber fabrics reinforced epoxy resin tabs are bonded to ends of the specimens using high elongation adhesive system. Tensile test of pure resin was in accordance with GB/T 2567. One strain gauge was bonded to on the surface of the specimens to measure tensile strain.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompressive test\u003c/strong\u003e \u003cp\u003eCompressive properties of CFRP were performed based on ASTM D6641 using LE055 with a load speed of 1.3mm/min. Two strain gauges were bonded to on the back and front surfaces of specimen to record tensile strain and monitor percent bending. Compressive test of pure resin was in accordance with GB/T 2567.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eIn-plane shear test\u003c/strong\u003e \u003cp\u003eShear properties of CFRP were performed in compliance with ASTM D7078 using LE055 with a load speed of 2 mm/min. Two 120-5AA gauges were bonded to on the surface of the specimens in an angle of 45\u0026deg; with fiber direction to calculate shear strain.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eInterlaminar shear strength test\u003c/strong\u003e \u003cp\u003eInterlaminar shear strength of CFRP was tested consistent with ASTM D2344 using LE055 with a load speed of 1 mm/min. Seven specimens were prepared per test condition and effective values after screening were preserved. Commonly, 3\u0026ndash;6 valid data are retained after excluding the unacceptable failure modes and abnormal data.\u003c/p\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Weight change\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the evolution of surface morphologies over aging time for the pure resin immersed into deionized water and artificial seawater using SEM. The unsmooth appearance of unaged resin specimens with certain amounts of wrinkles in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea were observed due to the forming of residual stress in the casting process. After immersion for 168 hours in two harsh environments, the appearance has changed to be smooth because of the release of residual stress caused by the moisture diffusion into resin which was commonly accompanied by the generation of the swelling stress (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Subsequently, the circle-like superficial pits initiated on the smooth surface of resin specimens immersed in deionized water (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), but this phenomenon didn\u0026rsquo;t arise in those immersed in the artificial seawater (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). With the increase in immersion duration, the smaller pits grew greatly in appearance, even extensive voids emerged in the deep layers to form a pathway for the ingress of moisture after immersion for 2160 hours for the resin specimen in deionized water (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The formation of pits and voids from SEM observation results demonstrates that the partial substances were lost during immersion period.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the FTIR spectrums for pure resin immersed in deionized water and the characteristic peaks of used epoxy bisphenol vinyl resin before aging were labeled in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The spectrum displays a broad peak at 3454 \u003cem\u003ecm\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e that is related to the stretching vibration of hydroxyl (-OH) groups. As the immersion duration increased, the characteristic peak of hydroxyl groups gradually became broader and stronger in company with the movement to a lower wavenumber (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), revealing that the resin molecular chains were associated with water molecular in the form of hydrogen bonds to form bound water. It is because that the aggregation of water molecules and the formation of hydrogen bond not only increased the intensity of hydroxyl stretching vibration but also reduced the stretching vibration frequency. In addition, the peaks at 758 \u003cem\u003ecm\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e and 700 \u003cem\u003ecm\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;1\u003c/em\u003e\u003c/sup\u003e, which were associated with C-H out-of-plane bending vibration from benzene ring, disappeared after immersion in deionized water for 2160 hours (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). This could be explained by the fact that the pure resin underwent severe hydrolysis, and the hydrolysates were lost in the medium. Therefore, the change in surface morphologies for the resin immersed in deionized water was induced by the moisture uptake and hydrolysis. As a comparison, the crazing occurred and accumulated in the appearance of specimens with the prolongation of immersion in artificial seawater, which was due to the increase of swelling stress (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). And after immersion for 2160 hours, the crazing evolved to the small crakes and very tiny pits arose in the appearance (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg), showing that hydrolysis also occurred at this stage but was of relatively weak intensity compared to the resin specimens immersed in deionized water during same immersion duration. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e depicts the development of surface morphologies of CFRP specimens immersed in deionized water and artificial seawater. Clearly, changes in morphology are invisible during the entire duration of the immersion. i.e. the hydrolysis in the resin matrix is weakened due to the embedment of carbon fiber which is hydrophobic and corrosion-resistant.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e gives the measured data for the change in weight of pure resin and CFRP specimens immersed under two prescribed humid conditions, together with the fitted curves. Considering the usage of PTFE to prevent moisture diffusion along the side faces, one-dimensional equation for Fickian diffusion using Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) was adopted to fit the measured values. The detailed parameters for fitted curves are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Resin specimens immersed in artificial seawater and deionized water behaved in the distinct trends of the moisture absorption (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). The former appeared to correspond to Fickian diffusion behavior, i.e. the curve of moisture absorption in initial stage was a linear function of square root of time, followed by an equilibrium saturation value of water uptake of 1.0% after the immersion of 2160 hours. But the weight slightly fluctuated in the final plateau phase of curve, departing from the characteristics of Fickian model to some extent. From previously published literature, the occurrence of hydrolysis affected the equilibrium mass uptake. From the SEM observation results in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg, we can know that relatively weak hydrolysis happened and resulting hydrolysis-controlled moisture absorption and mass loss brought about the deviation from the behavior of Fickian diffusion. Comparatively, the resin specimens immersed in deionized water appreciably followed the non-Fickian diffusion especially in the plateau phase (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). In initial stage of immersion, the weight change for resin immersed in deionized water also approximately linearly varied with square root of time, but subsequently fluctuated dramatically in the transition region, and finally the weight change kept relatively stable and slowly increased with the immersion time. Combined with SEM images in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-d and FTIR spectrogram in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, it can be inferred that the dramatic wave of weigh in the initial plateau region resulted from the coupling of diffusion-controlled moisture absorption as well as hydrolysis-controlled moisture absorption and material loss. And the slight increase of weight in the last region of curve was dominated by hydrolysis-controlled moisture absorption. In contrast to resin specimens, CFRP specimens immersed into deionized water and artificial seawater nearly conformed to the Fickian diffusion with stable saturation level of 0.32% and 0.31%, respectively (see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), and coefficients of diffusivity in the seawater was slightly larger than that in deionized water. Through Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the water absorption of CFRP is significantly lower than pure resin. To clarify the role of carbon fiber on the water uptake of composites, the weight of carbon fiber is excluded for the calculation of weight change of CFRP in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and modified results are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. The moisture absorption of resin matrix in CFRP is still lower than the pure resin in the same conditions, revealing that the carbon fiber inhibited the ingress of water into composites. Additionally, to differentiate the contribution of moisture uptakes and mass loss to weight change, the final masses of the pure resin and CFRP specimens immersed in deionized water were weighted after the aged specimens immersed in deionized water for 2160 hours were dried at 40\u0026deg;C for 800 hours (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). The final weight of the pure resin and CFRP specimens were reduced by 0.28% and 0.039% as compared to the unaged specimens. It reveals again that weight change of resin immersed into deionized water arose from the mass loss by hydrolysis as well as moisture uptake by diffusion and hydrolysis. And the hydrolysis could be neglectable for the CFRP specimens, i.e. weight change of CFRP was induced by the diffusion-controlled water uptake.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe non-linear fitted parameters for Fickian diffusion\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItems\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEffective equilibrium water uptake (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varvec{M}}_{\\varvec{\\infty }})\\)\u003c/span\u003e\u003c/span\u003e/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDiffusion coefficient (\u003cem\u003eD\u003c/em\u003e)/mm\u003csup\u003e2\u003c/sup\u003e\u0026bull;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCoefficient of determination (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResin in deionized water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResin in artificial seawater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.047\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCFRP in deionized water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCFRP in artificial seawater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCFRP in deionized water (excluding mass of fiber)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCFRP in artificial seawater\u003c/p\u003e \u003cp\u003e(excluding mass of fiber)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.047\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Degradation of mechanical properties\u003c/h2\u003e \u003cp\u003eThe fluctuation in tensile strength with immersion duration for pure resin and CFRP specimens is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Meanwhile, the typical tensile stress-strain curves for unaged specimens and aged ones for 2160 hours in deionized water are provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. In accordance with the test standard, the tensile moduli of the resin and CFRP were calculated from the slope between the two points where their strain values are 0.001 and 0.003, respectively. The tensile strength of resin significantly decreased in the first experimental examination after immersion for 168 hours, with a 34.2% reduction from 46.7MPa to 30.7MPa and then maintained small waves in the remainder of deionized water immersion. And the same trend was observed for resin immersed in artificial seawater (see Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Similarly, the modulus of aged resin declined significantly, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. It is well known that swelling stress due to moisture absorption is generally accompanied by the plasticization which reduces mechanical properties, and mass loss by hydrolysis also can also cause many local defects and lowers the mechanical properties. From SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and corresponding analyses, it can be inferred that degradation of resin properties in deionized water is jointly affected by hydrolysis and plasticization, and deterioration of resin properties in artificial seawater is mainly due to the plasticization.\u003c/p\u003e \u003cp\u003eFigs.7b\u0026nbsp;depicts the deterioration of tensile strength of CFRP specimens, and the typical tensile stress-strain curve is also added in Fig.8. Meanwhile,\u0026nbsp;Fig.13a\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003edisplays the typical and effective failure modes of CFRP tensile specimens with lateral and multi-modes failure types at the middle location of gauge area. Slightly different from the hygroscopic degradation of tensile properties for resin, there was the maximum reduction of 6.1% for the strength as compared to the virgin values for CFRP immersed in deionized water and artificial seawater, respectively. Moreover, the tensile modulus of aged composites was nearly equal to that of unaged composites. By comparing the stress-strain curves of the resin and the CFRP, it can be concluded that the fracture elongation of resin was larger than that of fiber, therefore the carbon fiber fractured before the matrix cracked during the damage of the composite. In short, the tensile properties of CFRP is not sensitive to deionized water and artificial seawater environment. It may be because of two reasons. One is that the tensile strength is mainly dominated by the carbon fiber whose properties can be regarded invariable during immersion duration, the other reason is that no obvious hydrolysis occurs in the resin matrix for CFRP specimens during immersion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig.9 displays the variations in compressive strength of pure resin and CFRP specimens with soaking duration, combined with typical failure modes of HAT, M(dh)GV where the measured data can be viewed as acceptable (Fig.13b). The typical stress-strain curves of resin and CFRP are also given in Fig.10. The strength of resin degraded inconsiderably in the vicinity of average value of 100 MPa with a fluctuation of \u0026plusmn;2 MPa, showing that the absorbed moisture and mass loss have not influenced the compressive behavior of resin (see Fig.9a). By contrast, the compressive strength of CFRP declined markedly initially and then stabilized in the subsequent immersion duration. To be specific, the compressive strength fell a great deal in the first examination from 638 MPa to 559 MPa and kept a fluctuation of 20 MPa in the next examinations (see Fig.9b).\u0026nbsp;\u003c/p\u003e\u003cp\u003eThe compressive modulus of the resin was computed based on the slope of curves in Fig.\u0026nbsp;10. The modulus of resin waved slightly after immersion for 2160 hours. Similarly, the compressive modulus of aged CFRP as the slope of stress-strain curve between two points (strains of 0.001 and 0.003) also degraded inconsiderably. It is well known that the compressive strength is mainly determined by the fiber buckling which is relevant with resin properties, fiber properties interfacial properties between fiber and resin as well as interlaminar properties between plies. The degradation of compressive strength of resin can be omitted from aforementioned experimental data plus the impermeability of carbon fiber to moisture, the drop in compressive strength of CFRP specimens was therefore due to the weakening of interfacial properties or interlaminar properties. To clarify the reason for the reduction of compressive strength of CFRP, the deterioration of interfacial and interlaminar properties was investigated below.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe measured shear strength of CFRP is plotted in Figs.\u0026nbsp;11a, along with the typical and acceptable failure modes of shear test in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ec. Horizontal cracking in gauge area between notches was encountered can be regarded as the valid failure mode. The shear strength in Fig.\u0026nbsp;11a was nearly constant during immersion in deionized water and artificial seawater. The stress-strain curve for in-plane shear test for CFRP is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. Likewise, the shear modulus as the slope between two points (strains of 0.002 and 0.006) also fell slightly. Shear modulus is mostly dominated by the resin properties, therefore the reduction in shear modulus can be viewed as the softening and increase in flexibility of resin matrix. Meanwhile, shear strength of CFRP can be deemed as an indicator of deterioration of interfacial properties between fiber and resin, and the stable shear strength of CFRP in Fig.\u0026nbsp;11a indicates a negligible degradation of interfacial properties. Figure\u0026nbsp;11b gives the interlaminar shear strength (ILSS) of CFRP specimens from short beam testing where the typical and effective failure modes of specimen are the delamination of layer in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ed. Clearly, ILSS of specimens immersed in deionized water and artificial water respectively showed the reduction of 13.5% and 10.0% after immersion for 2160 hours from 67.9 MPa to 58.7 MPa and 59.6 MPa, showing the severe worsening of interlaminar properties. Observing the trend of material properties degradation with immersion time in Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003e, \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e and 11, it is easily found that the reduction in properties for CFRP mainly occurred before two weeks\u0026rsquo; immersion. The properties degradation is commonly caused by the moisture absorption and material loss. From previous analyses, it is known that the material loss can be negligible due to weak hydrolysis reaction for CFRP specimens. In combination with the results in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, i.e. the amount of water absorption for CFRP is a linear function of square root of time (t) and after about two weeks\u0026rsquo; immersion, weight nearly keep stable. Therefore, the main properties degradation mainly occurs in the early stage of immersion. Meanwhile, noted that the measured data at some certain time exhibit big deviation from the average value, this is because that mechanical properties of composites show inherent deviation in the properties of constituent materials, especially for the fiber. Moreover, multiple failure modes which can be accepted based on the test standards further aggravate the deviation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFinally, the retention of strength for CFRP and resin specimens after immersion into deionized water and seawater for 2160 hours is summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e. From the ranking of reduction in magnitude, the tensile strength of pure resin specimens dropped most significantly, only with a retention of 64.5% of virgin value, and then the shear strength using short-beam tests for CFRP specimens retained 86.5% of virgin value. The other strength properties deteriorate inconsiderably with a retention of above 90%, even had a slight increase of 1% for compressive strength of resin. Meanwhile, the extent of degradation of the mechanical strength of CFRP and resin under deionized water and artificial water are nearly the same.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe following conclusions can be obtained that:\u003c/p\u003e \u003cp\u003e(1) SEM observation results in combination with FTIR images and curves of weigh change show that strong hydrolysis occurs for pure resin in deionized water. The resulting weight change with immersion duration behaves in non-Fickian diffusion, while the CFRP specimens approximately follows the Fickian diffusion due to the embedment of carbon fiber inhibiting the hydrolysis reaction.\u003c/p\u003e \u003cp\u003e(2) The degradation of resin properties in deionized water is jointly affected by hydrolysis and plasticization, while the deterioration of resin properties in artificial seawater is mainly due to the plasticization. Meanwhile, the moisture diffusion into resin has a minor effect on the compressive behavior.\u003c/p\u003e \u003cp\u003e(3) The properties degradation of CFRP specimens immersed in deionized water and artificial seawater is dominated by the diffusion-controlled moisture uptakes. Tensile and compressive properties deteriorate insignificantly, and main reductions occur in interlaminar shear strength for CFRP, with loss of 13.5% after 2160 hours\u0026rsquo; immersion.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eCompeting Interests：This study was funded by the Fundamental Research Funds for the Central Universities (WUT:203101002, 203201006)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eW. 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Tarpani, S.C. Amico, Accelerated Ageing Effects on Short-Beam Strength Behavior of Pultruded CFRP Rods, Applied Composite Materials 29(2) (2022) 855-869.\u003c/li\u003e\n\u003cli\u003eC.-H. Shen, G.S. Springer, Moisture Absorption and Desorption of Composite Materials, Journal of Composite Materials 10(1) (1975) 2-20.\u003c/li\u003e\n\u003cli\u003eJ. Zhou, J.P. Lucas, Hygrothermal effects of epoxy resin. Part I: the nature of water in epoxy, Polymer 40(20) (1999) 5505-5512.\u003c/li\u003e\n\u003cli\u003eY. Wang, W. Zhu, B. Wan, Z. Meng, B. Han, Hygrothermal ageing behavior and mechanism of carbon nanofibers modified flax fiber-reinforced epoxy laminates, Composites Part A: Applied Science and Manufacturing 140 (2021) 106142.\u003c/li\u003e\n\u003cli\u003eH.G. Carter, K.G. Kibler, Langmuir-type model for anomalous moisture diffusion in composite resins, Journal of Composite Materials 12(2) (1978) 118-131.\u003c/li\u003e\n\u003cli\u003eT. Peret, A. Clement, S. Freour, F. Jacquemin, Numerical transient hygro-elastic analyses of reinforced Fickian and non-Fickian polymers, Composite Structures 116 (2014) 395-403.\u003c/li\u003e\n\u003cli\u003eD.K. Jesthi, R.K. Nayak, Evaluation of mechanical properties and morphology of seawater aged carbon and glass fiber reinforced polymer hybrid composites, Composites Part B: Engineering 174 (2019) 106980.\u003c/li\u003e\n\u003cli\u003eR. Martin, Ageing of composites, Elsevier2008.\u003c/li\u003e\n\u003cli\u003eP. Davies, Y.D. Rajapakse, Durability of composites in a marine environment, Springer2016.\u003c/li\u003e\n\u003cli\u003eB.G. Kumar, R.P. Singh, T. Nakamura, Degradation of carbon fiber-reinforced epoxy composites by ultraviolet radiation and condensation, Journal of Composite materials 36(24) (2002) 2713-2733.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"applied-composite-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acma","sideBox":"Learn more about [Applied Composite Materials](http://link.springer.com/journal/10443)","snPcode":"10443","submissionUrl":"https://submission.nature.com/new-submission/10443/3","title":"Applied Composite Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"CFRP, Vinylester resin, Moisture absorption, Aging, Mechanical properties","lastPublishedDoi":"10.21203/rs.3.rs-3623857/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3623857/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe hygrothermal aging of vinylester resin and its carbon fiber fabric reinforced composite structures are examined here, including moisture absorption and the resulting degradation of mechanical properties. The prepared resin casting and CFRP specimens were immersed into the deionized water and artificial seawater, respectively, at a temperature of 70\u0026deg;C, and weighed regularly along with the observation of surface morphologies using SEM and identification of variations in functional groups using FTIR spectrometer. Meanwhile, the mechanical properties of resin and CFRP were checked periodically. The results from gravimetric analysis show that resin immersed in deionized water behaves in non-Fickian diffusion due to strong hydrolysis, while CFRP obeys approximately the Fickian diffusion because of the embedded carbon fiber inhibiting the hydrolysis. The examination of mechanical properties for CFRP reveals that the interlaminar shear strength is influenced by the moisture absorption, with a maximum reduction of 13.5%.\u003c/p\u003e","manuscriptTitle":"Hygrothermal behavior of carbon fiber fabric reinforced vinylester resin composite structures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-11-23 22:35:25","doi":"10.21203/rs.3.rs-3623857/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2023-12-04T09:34:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-12-01T12:27:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"c63bf80c-4d22-4b79-9206-fe4430087685","date":"2023-11-21T07:36:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"238fe2d7-9884-457f-9773-e866b3a01d58","date":"2023-11-21T07:32:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-11-21T07:29:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-11-20T19:08:41+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-11-20T12:41:32+00:00","index":"","fulltext":""},{"type":"submitted","content":"Applied Composite Materials","date":"2023-11-17T05:19:50+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"applied-composite-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acma","sideBox":"Learn more about [Applied Composite Materials](http://link.springer.com/journal/10443)","snPcode":"10443","submissionUrl":"https://submission.nature.com/new-submission/10443/3","title":"Applied Composite Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1ac17e76-cbc2-4de6-bde8-2c5d776b9ec8","owner":[],"postedDate":"November 23rd, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-03-15T09:12:09+00:00","versionOfRecord":{"articleIdentity":"rs-3623857","link":"https://doi.org/10.1007/s10443-024-10216-1","journal":{"identity":"applied-composite-materials","isVorOnly":false,"title":"Applied Composite Materials"},"publishedOn":"2024-03-12 09:12:09","publishedOnDateReadable":"March 12th, 2024"},"versionCreatedAt":"2023-11-23 22:35:25","video":"","vorDoi":"10.1007/s10443-024-10216-1","vorDoiUrl":"https://doi.org/10.1007/s10443-024-10216-1","workflowStages":[]},"version":"v1","identity":"rs-3623857","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3623857","identity":"rs-3623857","version":["v1"]},"buildId":"ApUGefWb6u5IBVtyqm6d5","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}