Experimental study and failure mode analysis of off-axis compression behaviour in natural fibre polymer composite

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A study was conducted to investigate the effect of various fibre orientations on the compressive properties of the natural fibre composite. The primary phase of the composite is epoxy resin, while the secondary phase (filler) is the oil palm empty fruit bunch (OPEFB) fibres. The OPEFB-fibre composites were prepared using the vacuum-assisted resin transfer moulding (VARTM) technique. Compression test according to ASTM D695, scanning electron microscope (SEM), and Fourier transform infrared (FTIR) analysis were conducted on the specimens. The compressive strength results indicate the anisotropic behaviour of the polymer composite due to different fibre orientations, with the highest compressive strength found in 15° specimens. The observed failure modes of the composites were analysed and found to be consistent with the compressive strength results through both the SEM and the optical microscope images. Hybrid Composite Materials Oil Palm Empty Fruit Bunch Fibre Orientation Compressive Strength Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction As the world grapples with escalating environmental threats, the shift towards sustainable and eco-friendly materials has never been more urgent, as humanity needs to take charge in preserving nature against irreversible ecological damage [1]. This has led to the rise of the concept of sustainable development, where, transformative approach guided by laws and innovative practices aims to enhance resource efficiency [2],[3]. The pursuit of sustainable development has sparked significant interest in the field of natural fibre composites (NFCs) as it induces economic benefits aside from environmental advantage, with green materials contributing to energy savings, representing a worthwhile investment [4], [5]. Among these green materials, NFCs have emerged as a promising substitute for synthetic composites driven by their availability, biodegradability and booming market demand in lightweight materials [6]. According to the market analysis report by Grand View Research [7], NFCs are worth USD 9.44B as of 2024 and are expected to escalate 12% by 2025 to 2030. Due to this fact, materials have become increasingly popular in various industries, including automotive, aerospace, and construction, owing to their superior mechanical properties and lightweight characteristics [6]. In a recent 2024 advancement, Bcomp and TESLA integrated natural fibre composites into their racing car design, resulting in a weight reduction of 500 kg [8]. In light of the growing consciousness that the construction industry emits significant amounts of carbon and contributes heavily to environmental degradation [9]. NFCs are now being adopted in construction for interior components and load-bearing elements [6]. This leads to the introduction of green building materials, designed to provide sustainable and durable materials with minimal maintenance and reduce emissions and resource extraction [9]. NFCs have been applied in the aerospace industry – including Fighter jets, civil aircraft, helicopters and even satellites – for their ability to enhance fuel efficiency and manoeuvrability while simultaneously reducing environmental footprint [6]. Considering the rise in demand, these bio-based composites are expected to provide sufficient mechanical performance on par with their synthetic counterparts [10]. The fibre–matrix interaction plays a vital role in defining the overall properties, and significant efforts have gone into chemical treatments to improve interfacial adhesion and reduce moisture absorption. Selection of NFCs for engineering applications depends on fibre type, orientation, resin compatibility, and manufacturing techniques. One critical aspect of composite design is the orientation of the fibres, which can significantly impact the material's compressive strength. Fig.1 illustrates various fibre orientations (0º,15º,30º,45º,60º,75º,90º) commonly applied in polymer composites. The orientation will impact the distribution of stress under load, along with the tensile strength, which are vital to maintaining structural integrity. Fibre orientation at 0º usually exhibits premature fracture in the matrix due to uneven distribution of deformation [11]. Despite this, as shown in Table 1, most studies tend to prioritise tensile testing, impact, and flexural testing, leaving compression testing underrepresented in mechanical performance. This is notable as the compressive strength of composite materials, particularly those using fibre fabrics, can be a limiting factor in their structural application. This journal paper aims to explore the effect of fibre orientation on the compressive strength of natural fibre composite materials, where the compressive properties are often neglected when considering their overall performance. Table 1 Types of testing on polymer composites No. Author Year Fibres & reinforcements Mechanical testings 1. [12] 2024 Jute, Sisal & Egg shells Tensile, and flexural properties 2. [13] 2024 Bi-directionally woven jute plies Tensile modulus, and tensile strength 3. [14] 2023 Woven Kenaf Tensile, flexural, and impact properties 4. [15] 2024 Cotton, sisal, coir and wool fibres Tensile, and wear properties 5. [16] 2024 Short jute, silk, water hyacinth, and glass fibres Tensile, bending, and impact properties 6. [17] 2024 Hemp, Jute, Date palm fibre Compression, flexural, and impact properties 2 Background The compressive strength of unidirectional composites is largely governed by the microbuckling of fibres embedded in the matrix, with the fibre waviness identified as a major factor [ 18 ]. This behaviour contrasts with the tensile strength, where most advanced fibre composites are stronger. Additionally, the compressive properties of composites under flexural loads can also be a concern [ 18 ]. Extensive research has been conducted over the years on off-axis compression tests. Theoretical studies [ 19 ],[ 20 ],[ 21 ] have identified failure modes such as fibre splitting, interface decohesion, fibre kinking, and matrix shear failure, which have been widely observed and validated through experimental work. The compressive fracture mechanism of fibre-reinforced polymers (FRP), often induced by microbuckling of the fibres, is known as fibre kinking. Ma et al. [ 22 ] investigated the compressive behaviour of thermoplastic composites across various off-axis angles and observed that fibre kinking occurred predominantly in specimens with small off-axis angles (0° and 15°). [It was suggested that sufficient lateral support from the matrix caused fracture to occur via shear stress, rather than the typical microbuckling failure mode.] As the off-axis angle increased to 30°, failure transitioned primarily to matrix fracture. [Under compression along the fibre direction, fibre breakage led to debris formation, while matrix-fibre interaction induced debonding and the appearance of nodules.] Fibrillation was also reported due to void nucleation, growth, and coalescence under plastic deformation. At 45°, plastic shear damage and fibrillation became evident. For 60° specimens, [combined compression/shear stress caused fibre splitting and the fracture of short fibres]. Similarly, at higher angles (75° and 90°), this trend continued, with extensive fibre splitting and fracture dominating the failure surfaces. This result is also backed by Yang et. al [ 23 ], where it is observed that as the off-axis angles become larger, matrix cracking develops, leading to composite failure. In the composite where fibres are aligned with 10°, both fibre kinking and matrix cracking were observed simultaneously in two specimens, while the others were fractured by a single matrix crack. When the off-axis angle exceeds 10°, matrix cracking parallel to the fibre orientation, mainly through the centre of the specimen, becomes the main cause of failure. Two distinct failure modes can be further identified based on the orientation of the fracture plane. For specimens with off-axis angles of 15°, 20°, and 30°, the fracture plane is nearly perpendicular to the specimen surface, indicating that matrix failure is mainly due to in-plane shear. In contrast, for specimens with larger off-axis angles, the fracture surface tends to be noticeably inclined, suggesting a prevalent impact of radial compression. Furthermore, the movement of micro-voids between fibres is influenced by the local microstructure, particularly the local fibre volume fraction. It is also proven in another study [ 24 ] that the fibre volume fraction is utilised in determining the dominating failure mechanisms under compression, and therefore has a high impact on the prediction accuracy of various models. The presence and mobility of such voids are also affecting the wettability of resin and fibres. The rheological properties of the resin are also of an important parameter as well [ 25 ]. Sisodia et al . [ 26 ] stated that more voids were found in off-axis plies of a multidirectional laminate. According to the studies, voidage experienced increased difficulty in escaping when the resin streams through the off-axis channel as compared to the parallel ones. The occurrence of voidage caused an effect on the composite response to the loading through stress/ strain concentration effects, and through local deterioration of the material or interface strength, which finally caused the compressive properties to deteriorate. The study of Makeev et al . [ 27 ], stated that there is a lack of an accurate model in predicting the fibre-direction compressive strength for high-modulus (HM) carbon fibre composites. Due to the escalating demands from the industry, HM CFRP, which possesses a higher Young’s Modulus, is in demand. Therefore, they did a study on the fibre-direction compression strength performance using HM fibres in a way that will enhance microstructural stability. The compressive strength of various fibre resin combinations was found to have increased with the increase of the shear modulus to axial modulus ratio of the composite system. Thus, it is noteworthy that from the observation in the experiment, hybridising carbon fibre with different moduli can achieve the anticipated compressive strength of the composite. From the past literature, different composites with various off-axis angles have shown potential in terms of mechanical properties [ 28 ],[ 29 ],[ 30 ],[ 31 ]. However, there are no comprehensive reviews on the oil palm biomass reinforced composites with factors such as fibre orientation, fibre volume fraction and sizes of different fillers affecting the mechanical performance, primarily the compressive strength. The off-axis plies of the laminate exhibited lower compressive strength due to fibres slipping away from resins, and more voidage was found [ 22 ],[ 25 ],[ 26 ],[ 29 ]. There are also agglomeration issues that arose when a single filler particulate was introduced to the resin as a reinforcing filler [ 32 ]. Therefore, there is a clear research gap to evaluate the compressive behaviour of the hybrid composite by varying the fibre orientation and at the same time incorporating the secondary reinforcement fillers with different sizes (micro and nano) that are expected to minimise the agglomeration problem and further improve the compressive strength. The results of this research would be an added contribution to solving the low-compressive problems in producing composites for structural applications. In addition, this research project does not pose ethical issues. 3 Methodology 3.1 Experimental Procedure Figure 2 summarises the experimental flow chart. Oil palm empty fruit bunch (OPEFB) fibres were collected from the local oil palm mill (SOPB Sdn. Bhd.). The fruit bunch were then cleaned to remove mud and grease before being immersed in 5% alkaline solution (NaOH) to remove substances such as lignin, pectin and hemicellulose. After 24 hours of alkalinisation, the OPEFB fibres were rinsed with distilled water to remove the remaining sodium hydroxide before being dried in the oven for 24 hours. The OPEFB fibres were then combed using a special combing tool for straightening purposes, as shown in Fig. 3 (a). The fabrication process was done using the vacuum-assisted resin transfer moulding method (VARTM). Before starting the fabrication process, the vacuum cavity must be prepared. Once the mould-releasing wax was spread evenly on the plate surface, the fibres were then aligned on the plate surface and sealed to form the vacuum cavity. Appropriate usage of tacky tape was necessary to ensure a tightly secured seal to prevent air leakages. The leak test was performed for 15 minutes to ensure no air leakages. According to the high-performance industrial application, the vacuum state needs to be maintained, and the maximum acceptable leak rate must be controlled at 3–5 mBar (0.08–0.15 Hg) per minute [ 33 ]. Miracast 1517 A epoxy resin, and its hardener, Miracast 1517 B were poured into two separate cups. 150 g of epoxy was measured using the weighing balance and poured into a new cup. The disposable cup containing epoxy was then filled with 45 g of hardener. The mixture was manually stirred at about 120 rpm for 5 minutes. The resin transfer to the mould was facilitated using the injection pressure vacuum pump. Subsequently, the specimens were allowed to dry at room temperature and undergo a 24-hour curing process. The samples were removed from the vacuum seal and subjected to a post-curing procedure at 90°C for 2 hours. The specimens were then cut into cubical sizes according to the desired fibre orientation following ASTM D695 using the Lartone lapidary saw, as shown in Fig. 3 (b). The designation for the unidirectional oil palm empty fruit bunch (OPEFB) with different fibre orientations is shown in Table 2 . Table 2 Designation for unidirectional oil palm empty fruit bunch (OPEFB) series No Designated Name Type of filler Fibre Orientation Average total filler weight percentage (wt%) 1 OPEFB 0 OPEFB 0° ≈ 32 wt% 2 OPEFB 15 OPEFB 15° ≈ 32 wt% 3 OPEFB 30 OPEFB 30° ≈ 32 wt% 4 OPEFB 45 OPEFB 45° ≈ 32 wt% 5 OPEFB 60 OPEFB 60° ≈ 32 wt% 6 OPEFB 75 OPEFB 75° ≈ 32 wt% 7 OPEFB 90 OPEFB 90° ≈ 32 wt% 3.2 Compression Test The mechanical properties of the composite specimens under compression loading were investigated using the Instron 5982 universal testing machine (UTM) shown in Fig. 4 . Specimens for compression testing were evaluated according to the ASTM standard listed above using a 100 kN load cell and a crosshead rate of 1.3 mm min-1. Measurements of the width and thickness of the specimens are obtained using a digital micrometre. The standard shape of the specimen is cubical, with dimensions of 25.4 × 12.7 × 12.7 mm. Each composite composition was tested with ten specimens, for which the mean and standard deviations are presented in this work. 3.3 Optical Microscope & Scanning Electron Microscope (SEM) The microstructure analysis of the OPEFB-fibre composite specimens was conducted by examining the fracture surface of the composite using an optical microscope. The Thermo Scientific Quattro S scanning electron microscope and Olympus optical microscope were used for the observation of microstructural analysis, which includes the surface morphology, structure, and topology of the specimens. Each equipment offers information on failure criteria and types of failure of the fractured surface in the composite specimens, and identification of fibre fracture surface conditions with different magnifications. 4 Results This section presents the compressive strength of OPEFB fibre-reinforced composites, supported by failure behaviour observations and FTIR spectrum analysis. 4.1 Experimental Procedure Figure 5 shows the compressive strength of the unidirectional OPEFB series with different fibre orientation angles ranging from 0° to 90°. The weight percentage of OPEFB fibres used is approximately 32 wt%. OPEFB 15 composite offers the highest compressive strength, 75.66 MPa, a 6.5% improvement compared to the pure epoxy samples without OPEFB reinforcement at 71 MPa. It is followed by OPEFB 0, which exhibited a relatively good but slightly lower compressive strength performance of 69.77 MPa. The lowest compressive strength was observed in the largest off-axis value of the OPEFB 90 composite, which had a compressive strength of 39.52 MPa. A steady decline could be observed at off-axis angles of 30° onwards to 90°. The results shown are in line with the investigation conducted by the previous research, where OPEFB fibre composites were shown to have lower compressive strength at larger fibre orientation angles compared to samples of smaller fibre orientation angles [ 22 ],[ 34 ],[ 35 ]. The fibre content in all specimens was maintained at approximately 32 wt%. However, due to the nature of the fabrication process, achieving an exact weight percentage is not feasible. This is primarily because the volume of resin that flows into the cavity during the VARTM process cannot be precisely controlled prior to fabrication. As a result, the actual fibre content varied slightly, ranging between 30–33 wt%. It is noticeable from the bar chart, the compressive strength reduced, as the fibre orientation increased except for OPEFB 15. In typical situations, the specimens with fibres aligned (0°) would possess the highest strength properties as the longitudinal fibres placed in the load's direction could directly absorb, transfer, and distribute the load uniformly throughout the cross-section. However, in this study, the OPEFB 0 composite possessed slightly lower compressive strength than the OPEFB 15 composite. This could be caused by the arrangement of fibres in these specimens. In natural fibre composite, the reinforcing fibres act as the primary load-carrying component, while the matrix functions as a binder that binds with fibres and transfers loads between. The arrangement of fibres in OPEFB 0 was aligned along the load direction, causing the fibre to carry most of the load while the matrix played a relatively minor role in load transfer. Therefore, fibres experiencing heavy loads would form localised stress concentrations leading to premature failure caused by fibre fracture or buckling. For OPEFB 15, fibres were positioned at 15° angle, they were not perfectly aligned with the load direction. The slight deviation from the on-axis caused the fibres to experience less load-bearing burden, but still primarily aligned with the load. Compression forces tend to act more evenly across the composite, making the matrix play a crucial role in supporting the loads. The matrix functions more as a load-carrier by sharing the load with the fibres, resulting in a more favourable stress distribution or interaction between fibres and matrix. Therefore, 15° orientation specimens achieved a balance where fibres still contributed to strength but were not as dominant as those found in 0° orientation specimens while the matrix’s strength assisted in supporting the load more effectively. The results were aligned with the findings of Oh et. al [ 36 ] where the bearing strength of 15º fibre orientation specimens was found to be 7.56% higher compared to those of 0º orientation. The authors further elaborated on the load distribution as 0º fibre orientation directly absorbs the applied load. However, when the fibre is positioned in the off-axis direction (15º), the load is further decomposed into sinθ and cosθ components, distributing the stress into longitudinal and transverse directions. This reduces stress concentration and the occurrence and propagation of damage. Therefore, specimen (0º) experiences initial fracture comparatively faster than specimen (15º). According to Akhyar et al. [ 37 ], longer fibre length imparts higher strength in the direction of the fibre. When the composite is cut to different orientation angles, i.e., (0°, 15°, 30°), each sample's fibre length would differ. For instance, the specimens with a 15° orientation would have their fibre length longer than those of 0° due to the fibres being slightly tilted; thus, the compressive strength of OPEFB 15 was higher than OPEFB 0. Another possible reason for this scenario could be due to the fibre misalignment generated during the fabrication of the fibre composites. The fibre misalignment is a manufacturing defect created by fibre movement in the matrix. When the vacuum pump was turned on during the VARTM process, it might have influenced the compressive strength of the fibre composites [ 38 ],[ 39 ]. In general, the variation of the fibre misalignment is more significant in the hand-made fibre composites that require minimal involvement of equipment, and this is highly likely to be responsible for the reduction of the compressive strength in the OPEFB 0 composite samples [ 40 ]. The compressive strength of the hybrid composite was noticed to exhibit a decreasing trend at larger fibre angles, specifically from 30° onwards. The possible explanation for this scenario is that at larger fibre angles, i.e., transverse compression (fibre direction at 90°), the load-bearing capacity of off-axis specimens deteriorates due to the fact that the fibres start slipping as they are subjected to the load. The fibres mainly resist transverse stresses, making the fibre-matrix interface a critical weak point. The functional effectiveness of the epoxy matrix to act as the binder material to hold fibres in position while transferring external loads to internal reinforcement was reduced. This will lead to a strength reduction of the composite at higher fibre angles. 4.2 Failure mode analysis for OPEFB reinforced composite of various fibre orientation To enhance the understanding of failure behaviour and its relation to compressive strength, the surfaces of the specimens were analysed using the optical microscope. Figure 6 and Fig. 7 depict images taken from the optical microscope that illustrate the fracture surfaces of the OPEFB composites; random fibre fractures are observed, likely resulting from excessive bending during buckling post-matrix yielding. Additionally, a clean fibre surface signifies significant failure at the fibre-matrix interface. The fracture surface of OPEFB 0 specimens shows multiple fibre breaks and localised rotation of broken fibres. These fibre fractures indicate that fibre microbuckling might have occurred in these unidirectional composites. The mode of failure in the specimen subjected to longitudinal compression ( θ = 0°) was a mixed failure mode of fibre splitting/fracture with minimal fibre kinking along the fibre direction, as seen in Fig. 6 (a). In contrast, the fracture surface of OPEFB 15 shows multiple fibre kinking, with no obvious fibre fracture. The fibre kink failure mode was the dominant failure mode in specimens subjected to 15° off-axis fibres. Typically, unidirectional laminates tend to experience shear mode failure when subjected to off-axis compressive loading. However, under compressive loads applied in the fibre direction or in the case of OPEFB 15, where fibres are still primarily aligned with the load, failure commonly occurs due to micro-buckling or kinking of fibres within a localised region. Due to the randomly oriented nature of the fibres in the composite, this kind of failure is only found on the fibres oriented along the loading axis of the specimen. Comparing the fracture surface of both OPEFB 0 and OPEFB 15, the 0° orientation specimens showed more localised and pronounced shear bands, which indicates early fibre kinking. The cracks and damage propagate along the fibre direction, which leads to a more sudden and catastrophic splitting failure. Meanwhile, from Fig. 6 (b) , the 15° orientation specimen showed more distributed shear bands due to the slight fibre misalignment, causing composite failure to occur progressively in a controlled manner. The cracks also deflected more due to the off-axis fibres, leading to an increase in fracture resistance. The angled fibres are believed to have delayed the fibre-kinking process, thus improving the load-bearing capacity as more force is required to initiate fibre microbuckling. The results from the previous section also reflected that OPEFB 15 exhibited a slightly higher compressive strength than OPEFB 0. According to the longitudinal compression and smaller off-axis angles (i.e. θ = 0° and 15°), failure modes were mostly the combined in-plane and out-of-plane kink modes. The specimens that have fibre orientation of different axes show a cleaner failure. The off-axis compressive strength is also found to be affected by the dominant mode of failure. In the case of the OPEFB 30, OPEFB 45, OPEFB 60, OPEFB 75, and OPEFB 90 specimens, there seems to be considerable shear failure together with matrix tearing or cracking. In larger off-axis angles (i.e. θ = 45°, 60°, 75°, and 90°), shear failure of the matrix seems to be a dominant failure mode. Notably, the specimens that experienced fibre kinking or micro buckling had higher strength compared to those that failed in a matrix-dominated mode. This suggests that friction on the contact surfaces was not eliminated during the testing of these two specimens, and thus, lateral constraint delayed the onset of matrix cracking. The specimens that experienced the combination of in-plane and out-of-plane kinking modes resulted in higher compressive strength compared to those of in-plane and out-of-plane shear modes. The increased compressive strength observed at a 15° fibre orientation is attributed to this kinking mechanism, whereas at angles greater than 30°, where shear modes dominate, compressive strength deteriorates. From the study of Kawai and Saito [ 35 ], these findings indicate that, if governed by typical compressive failure modes, the off-axis compressive strength tends to surpass the off-axis tensile strength across a variety of fibre orientations. When the off-axis angle exceeds 30°, the matrix cracking is aligned with the fibre orientation, and the primary failure mechanism typically occurs at the specimen’s centre. For specimens with off-axis angles of 45° and 60°, the fracture plane is nearly perpendicular to the specimen surface, which indicates that matrix failure is mainly caused by in-plane shear. Conversely, for specimens with larger off-axis angles, such as 75° and 90°, the fracture surface is observed as inclined, which signifies a predominant influence of transverse compression where fibres are mainly resisting transverse stresses, making the fibre-matrix interface a critical weak point. From Fig. 7 (a) , the fibres appear to have separated from the surrounding matrix, which suggests a weak fibre-matrix interface. This is also characteristic of interfacial failure, where the bond between the fibre and matrix is compromised. From Fig. 7 (b) , the failure is dominated by poor fibre-matrix adhesion, where resin/matrix appears to be fractured, leading to cracks running along the matrix-rich regions. Figure 8 shows the macroscopic failure modes in off-axis compression for the specimens with θ = 0° to 90°, respectively. In cases of specimens with on-axis longitudinal compression and small off-axis angles, particularly 0° and 15° specimens, failure was also prominently influenced by fibre kinking induced by fibre micro buckling. These images also demonstrate that the specimens with the off-axis fibre orientations θ = 30°, 45°, 60°, 75°, and 90° failed along the fibre direction in a combined in-plane and out-of-plane matrix shear mode. For fibre orientations θ = 15° (OPEFB 15), only a single mode of failure was observed. The fracture surface was parallel with the fibres, and it was appreciably inclined from the through-the-thickness direction of the specimen, with no premature end collapse or splitting observed along the fibre direction. In contrast, the longitudinal compression ( θ = 0°, OPEFB 0) specimens experienced failure primarily due to both fibre splitting/ fracture and fibre kinking mode. This can be largely attributed to the direction of compression load application and the cross-sectional dimensions. The close-up view showcasing the presence of kink bands and fibres splitting in OPEFB 0 specimens using the SEM is shown in Fig. 9 . A unidirectional composite behaves almost like a linear elastic material when subjected to longitudinal tensile/compressive or transverse tensile loads. However, when exposed to transverse compressive loads, a unidirectional composite exhibits some degree of nonlinearity. Nevertheless, this nonlinearity is primarily attributed to matrix plasticity rather than interface damage [ 41 ]. The highest and lowest compressive strengths are found in OPEFB 15 and OPEFB 90, respectively. Therefore, the load-deformation curves of these two specimens were compared. From Fig. 10 , the uniaxial compressive load-deformation curves of both OPEFB fibre orientations of 90° (OPEFB 90) and 15° (OPEFB 15) are shown to be mostly single-peak curves. Peak deformations of OPEFB 90 specimens are up to 1–2 times as large as those of the OPEFB 15, thus showing that the deformation strength of OPEFB 90 specimens is higher. Fibre orientation has affected the strength of specimens and, at the same time, caused an influence on the deformation ability. The OPEFB 15 specimens were notably influenced by the material properties aligned with the fibre direction, as evidenced by the graph in Fig. 10 , which depicts minimal non-linearity before failure. Consequently, the yield criterion was not met, resulting in a lack of ductility. Conversely, the experimental results for the OPEFB 90 specimens exhibited a more nonlinear behaviour, suggesting a potential for higher ductility. Although OPEFB 90 possessed much lower compressive strength, the deformation ability was still better than OPEFB 15, which possessed excellent compressive strength. Therefore, it is worth further investigating the ductility of the specimens, whether they still have good integrity after compressive damage and the ability to possess more residual bearing capacity during larger compressive deformations. For larger off-axis angles, compressive failure occurred predominantly in a single mode, combined in-plane and out-of-plane shear mode. Consequently, nearly identical stress-strain relationships were observed across different specimens for each of these fibre orientations. Notably, for fibre orientations such as ( θ = 45°, 60°, 75°, and 90°), the off-axis flow stress level in compression within the nonlinear range was significantly higher compared to smaller off-axis angles. This indicates that higher external stress is consistently required to induce off-axis nonlinear compressive deformation for these fibre orientations. 4.3 Fourier Transform Infrared (FTIR) The FTIR analysis of 0°, 15°, and 90° OPEFB epoxy composites provides insight into the fibre-matrix interactions and epoxy crosslinking efficiency is shown in Fig. 11 . While differences between orientations are observed, the variations in chemical bonding are rather moderate than drastic. There are no significant differences in terms of compound changes and chemical bonding changes. There are two main transmittance regions at low and high wavenumbers between 500–1800 cm⁻¹ and 2700–3500 cm⁻¹, respectively, aligned with the data reported previously [ 42 ],[ 43 ]. In the FTIR analysis of all three specimens, a broad absorption band was observed at 3325 cm⁻¹ indicating the presence of O-H stretching due to cellulose [ 44 ]. OPEFB 15 represented by 15° OPEFB + epoxy in this graph, have exhibited lower transmittance at this peak as comparison to the other two specimens, OPEFB 0 and OPEFB 90, represented by OPEFB 0° + epoxy and OPEFB 90° + epoxy. The 15° specimens show the lowest transmittance percentage, which indicates the maximum absorption, followed by the 0° and 90° specimens. Interestingly, the findings at this peak also reflect the higher compressive strength possessed by OPEFB 15. While at the peak near 1700 cm⁻¹, corresponding to the C = O (carbonyl) stretching, was also found in all three specimens of different orientations. The peak was found to be slightly more shifted at 15° (OPEFB 15), meaning more chemical interaction might have occurred. The OPEFB fibre surface might be more exposed or react better with the epoxy functional group in OPEFB 15 specimens. This might be due to the longer fibre in the specimens compared to OPEFB 0 and OPEFB 90. The 15° composite also showed a slight reduction in transmittance compared to the specimens of 0° and 90°, though the differences are not substantial enough to suggest a major structural change. In the 1000–1250 cm⁻¹ region, which signifies the C-O-C stretching (cellulose bond), confirming the ether linkages in the epoxy network and its cross-linked structure[ 45 ]. At wavenumber 1029 cm⁻¹, the OPEFB 15 exhibited a slightly increased peak intensity, followed by OPEFB 0 and OPEFB 90, which may imply better epoxy crosslinking for OPEFB 15 as there are more reacted epoxy. However, all the other specimens, OPEFB 0 and OPEFB 90, also showed the occurrence of these key functional groups, which signifies that adhesion is present across all specimens with only moderate variations. OPEFB 15 also has the lowest transmittance in this region. 5 Conclusions As concerns about the depletion of natural resources continue to rise, there is a growing urge to utilise renewable resources like oil palm empty fruit bunch (OPEFB) in composite manufacturing. Thus, it can be expected that the upshot of this research will enlighten the upliftment of the compressive properties of natural fibre-reinforced composite. The scientific significance of the research includes: It is hypothesised that the study of different fibre orientations would help to identify the effective parameter of the composite with improved compressive properties. From different fibre orientations of OPEFB fibres being reinforced in the epoxy, it was found that OPEFB 15 ( θ =15°) showed the most consistent and highest compressive strength properties, even compared to the pure epoxy specimens. The lowest compressive strength was possessed by the OPEFB 90 specimens ( θ =90°). The main reason for the strength to deteriorate is that the transverse compression does not have the load-bearing capability as the load direction is perpendicular to the fibre’s direction. It is also worth highlighting that although the composite has low compressive properties, the deformation ability is higher than those with higher compressive properties. The failure behaviour of these composites could be examined by analysing the fracture surface of specimens. The type of failure modes and behaviour of composites strongly differ according to their relative fibre orientations. OPEFB 15 with the highest compressive strength exhibited kink-band failure, which is induced by fibre microbuckling, while the lowest compressive strength, OPEFB 90, showed matrix tearing/ cracking failure. The FTIR analysis also confirmed that OPEFB 15 exhibited the strongest fibre-matrix interaction, best curing, and overall improved bonding performance. Declarations Acknowledgements Fong Ai Ling and Amanda Mu acknowledge the Curtin Malaysia Postgraduate Research Scholarship (CMPRS) from Curtin Malaysia Graduate School. Fong Ai Ling would also like to thank the School of Pre-U and Continuing Education (SPACE) from Curtin Malaysia. Furthermore, the authors would like to express their gratitude to Curtin University Australia, Glasgow Caledonian University, and University Kuala Lumpur (UniKL). Author Contributions Fong Ai Ling: Investigation, Visualisation, Writing( Original Draft), Writing (Review & Editing. Amanda Mu: Conceptualisation, Investigation, Visualisation, Writing– Review & Editing. Lau Shiew Wei & Sujan Debnath: Conceptualisation, Visualisation, Writing– Review & Editing, Supervision. Mahmood Anwar, Ian J. Davies & Mahzan Bin Johar: Methodology, Language checking, Supervision. Funding This research did not received funding. 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2","display":"","copyAsset":false,"role":"figure","size":56358,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental Flow chart\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/0414dec5aa541b59aa7564d4.jpg"},{"id":98777541,"identity":"43d9a537-2f7c-42e9-9366-618f70663033","added_by":"auto","created_at":"2025-12-22 12:27:57","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":140680,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Combed OPEFB fibres (b) Cubical OPEFB fibre-reinforced composite specimens\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/0ce7db7aadb562b81a1f59a5.jpg"},{"id":98778948,"identity":"c7926d55-51ac-4319-958a-74792eb43c83","added_by":"auto","created_at":"2025-12-22 12:29:51","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":57952,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive test setup for the composite specimens\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/0bd07aab8dabfb95e79a178b.jpg"},{"id":98780150,"identity":"d1c213c1-096e-4937-ac27-4d560b62a02a","added_by":"auto","created_at":"2025-12-22 12:31:07","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":40393,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of OPEFB unidirectional series composite\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/73bf80425a3589a0a242f2ce.jpg"},{"id":98779378,"identity":"2a976a6e-b486-4578-b548-04a500f8bd4f","added_by":"auto","created_at":"2025-12-22 12:30:17","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":130122,"visible":true,"origin":"","legend":"\u003cp\u003e(a) fibre fracture of OPEFB 15 specimens (b) fibre kinking of OPEFB 0 specimens\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/c9f0361bfa71dd8904a4715e.jpg"},{"id":98778539,"identity":"2b2871fa-8a55-41b5-8182-04ad11358685","added_by":"auto","created_at":"2025-12-22 12:29:25","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":113095,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Side view of fracture surface showing debonding (b) Fracture surface of OPEFB 90 specimens\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/18fb234b8167709f1fda23ed.jpg"},{"id":98755256,"identity":"686cfbaa-1942-4adf-b21f-2ae3baa0a596","added_by":"auto","created_at":"2025-12-22 09:26:31","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":72178,"visible":true,"origin":"","legend":"\u003cp\u003eMacroscopic failure modes images of the on-axis and off-axis specimens.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/ba8fc2ef418b6c0a372da421.jpg"},{"id":98755237,"identity":"6a31dfb2-65fe-45de-879f-0b40d3ca341f","added_by":"auto","created_at":"2025-12-22 09:26:30","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":92728,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of OPEFB 0 showing fibre splitting and kinking\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/a1ce492edd3762e377eaa0f7.jpg"},{"id":98755244,"identity":"93bad401-0780-4ed4-934c-1b5d16b24d68","added_by":"auto","created_at":"2025-12-22 09:26:30","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":127150,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the load vs deformation graph of OPEFB 15 and OPEFB 90\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/3413fd61623a623a678aa2cc.jpg"},{"id":98755263,"identity":"a7fae414-2474-4985-b5d5-46af7d449a98","added_by":"auto","created_at":"2025-12-22 09:26:31","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":78638,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of OPEFB series (OPEFB 15, OPEFB 0, and OPEFB 90)\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/8140c247e233afcbdd1fdc38.jpg"},{"id":98784113,"identity":"80a87018-85d4-4ebe-ab61-87c0c25dab12","added_by":"auto","created_at":"2025-12-22 12:42:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1740699,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8323000/v1/320c470a-c25a-4cef-ae9e-d5b2b931ef7a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental study and failure mode analysis of off-axis compression behaviour in natural fibre polymer composite","fulltext":[{"header":"1 Introduction ","content":"\u003cp\u003eAs the world grapples with escalating environmental threats, the shift towards sustainable and eco-friendly materials has never been more urgent, as humanity needs to take charge in preserving nature against irreversible ecological damage [1]. This has led to the rise of the concept of sustainable development, where, transformative approach guided by laws and innovative practices aims to enhance resource efficiency [2],[3]. The pursuit of sustainable development has sparked significant interest in the field of natural fibre composites (NFCs) as it induces economic benefits aside from environmental advantage, with green materials contributing to energy savings, representing a worthwhile investment \u0026nbsp;[4], [5]. Among these green materials, NFCs have emerged as a promising substitute for synthetic composites driven by their availability, biodegradability and booming market demand in lightweight materials [6]. According to the market analysis report by Grand View Research [7], NFCs are worth USD 9.44B as of 2024 and are expected to escalate 12% by 2025 to 2030.\u003c/p\u003e\n\u003cp\u003eDue to this fact, materials have become increasingly popular in various industries, including automotive, aerospace, and construction, owing to their superior mechanical properties and lightweight characteristics [6]. In a recent 2024 advancement, Bcomp and TESLA integrated natural fibre composites into their racing car design, resulting in a weight reduction of 500 kg [8]. In light of the growing consciousness that the construction industry emits significant amounts of carbon and contributes heavily to environmental degradation [9]. NFCs are now being adopted in construction for interior components and load-bearing elements [6]. This leads to the introduction of green building materials, designed to provide sustainable and durable materials with minimal maintenance and reduce emissions and resource extraction [9]. NFCs have been applied in the aerospace industry \u0026ndash; including Fighter jets, civil aircraft, helicopters and even satellites \u0026ndash; for their ability to enhance fuel efficiency and manoeuvrability while simultaneously reducing environmental footprint [6]. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConsidering the rise in demand, these bio-based composites are expected to provide sufficient mechanical performance on par with their synthetic counterparts [10]. The fibre\u0026ndash;matrix interaction plays a vital role in defining the overall properties, and significant efforts have gone into chemical treatments to improve interfacial adhesion and reduce moisture absorption. Selection of NFCs for engineering applications depends on fibre type, orientation, resin compatibility, and manufacturing techniques. One critical aspect of composite design is the orientation of the fibres, which can significantly impact the material\u0026apos;s compressive strength. \u003cem\u003eFig.1\u0026nbsp;\u003c/em\u003eillustrates various fibre orientations (0\u0026ordm;,15\u0026ordm;,30\u0026ordm;,45\u0026ordm;,60\u0026ordm;,75\u0026ordm;,90\u0026ordm;) commonly applied in polymer composites. The orientation will impact the distribution of stress under load, along with the tensile strength, which are vital to maintaining structural integrity. Fibre orientation at 0\u0026ordm; usually exhibits premature fracture in the matrix due to uneven distribution of deformation [11]. Despite this, as shown in \u003cem\u003eTable 1,\u0026nbsp;\u003c/em\u003emost studies tend to prioritise tensile testing, impact, and flexural testing, leaving compression testing underrepresented in mechanical performance. This is notable as the compressive strength of composite materials, particularly those using fibre fabrics, can be a limiting factor in their structural application. This journal paper aims to explore the effect of fibre orientation on the compressive strength of natural fibre composite materials, where the compressive properties are often neglected when considering their overall performance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e Types of testing on polymer composites\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"465\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo.\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAuthor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eYear\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFibres \u0026amp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ereinforcements\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMechanical testings\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e1.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[12]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eJute, Sisal \u0026amp; Egg shells\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eTensile, and\u0026nbsp;flexural\u0026nbsp;properties\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e2.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[13]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eBi-directionally woven jute plies\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eTensile modulus,\u0026nbsp;and tensile\u0026nbsp;strength\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e3.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[14]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eWoven Kenaf\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eTensile, flexural, and impact properties\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e4.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[15]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eCotton, sisal, coir and wool fibres\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eTensile, and\u0026nbsp;wear\u0026nbsp;properties\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e5.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[16]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eShort jute, silk, water hyacinth, and glass fibres\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eTensile, bending, and impact\u0026nbsp;properties\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 42px;\"\u003e\n \u003cp\u003e6.\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e[17]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e2024\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eHemp, Jute, Date palm fibre\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 165px;\"\u003e\n \u003cp\u003eCompression, flexural, and impact properties\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"2 Background","content":"\u003cp\u003eThe compressive strength of unidirectional composites is largely governed by the microbuckling of fibres embedded in the matrix, with the fibre waviness identified as a major factor [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. This behaviour contrasts with the tensile strength, where most advanced fibre composites are stronger. Additionally, the compressive properties of composites under flexural loads can also be a concern [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eExtensive research has been conducted over the years on off-axis compression tests. Theoretical studies [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e],[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e],[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] have identified failure modes such as fibre splitting, interface decohesion, fibre kinking, and matrix shear failure, which have been widely observed and validated through experimental work. The compressive fracture mechanism of fibre-reinforced polymers (FRP), often induced by microbuckling of the fibres, is known as fibre kinking. Ma et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] investigated the compressive behaviour of thermoplastic composites across various off-axis angles and observed that fibre kinking occurred predominantly in specimens with small off-axis angles (0\u0026deg; and 15\u0026deg;). [It was suggested that sufficient lateral support from the matrix caused fracture to occur via shear stress, rather than the typical microbuckling failure mode.] As the off-axis angle increased to 30\u0026deg;, failure transitioned primarily to matrix fracture. [Under compression along the fibre direction, fibre breakage led to debris formation, while matrix-fibre interaction induced debonding and the appearance of nodules.] Fibrillation was also reported due to void nucleation, growth, and coalescence under plastic deformation. At 45\u0026deg;, plastic shear damage and fibrillation became evident. For 60\u0026deg; specimens, [combined compression/shear stress caused fibre splitting and the fracture of short fibres]. Similarly, at higher angles (75\u0026deg; and 90\u0026deg;), this trend continued, with extensive fibre splitting and fracture dominating the failure surfaces.\u003c/p\u003e \u003cp\u003eThis result is also backed by Yang \u003cem\u003eet. al\u003c/em\u003e [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], where it is observed that as the off-axis angles become larger, matrix cracking develops, leading to composite failure. In the composite where fibres are aligned with 10\u0026deg;, both fibre kinking and matrix cracking were observed simultaneously in two specimens, while the others were fractured by a single matrix crack. When the off-axis angle exceeds 10\u0026deg;, matrix cracking parallel to the fibre orientation, mainly through the centre of the specimen, becomes the main cause of failure. Two distinct failure modes can be further identified based on the orientation of the fracture plane. For specimens with off-axis angles of 15\u0026deg;, 20\u0026deg;, and 30\u0026deg;, the fracture plane is nearly perpendicular to the specimen surface, indicating that matrix failure is mainly due to in-plane shear. In contrast, for specimens with larger off-axis angles, the fracture surface tends to be noticeably inclined, suggesting a prevalent impact of radial compression.\u003c/p\u003e \u003cp\u003eFurthermore, the movement of micro-voids between fibres is influenced by the local microstructure, particularly the local fibre volume fraction. It is also proven in another study [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] that the fibre volume fraction is utilised in determining the dominating failure mechanisms under compression, and therefore has a high impact on the prediction accuracy of various models. The presence and mobility of such voids are also affecting the wettability of resin and fibres. The rheological properties of the resin are also of an important parameter as well [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Sisodia \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] stated that more voids were found in off-axis plies of a multidirectional laminate. According to the studies, voidage experienced increased difficulty in escaping when the resin streams through the off-axis channel as compared to the parallel ones. The occurrence of voidage caused an effect on the composite response to the loading through stress/ strain concentration effects, and through local deterioration of the material or interface strength, which finally caused the compressive properties to deteriorate.\u003c/p\u003e \u003cp\u003eThe study of Makeev \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], stated that there is a lack of an accurate model in predicting the fibre-direction compressive strength for high-modulus (HM) carbon fibre composites. Due to the escalating demands from the industry, HM CFRP, which possesses a higher Young\u0026rsquo;s Modulus, is in demand. Therefore, they did a study on the fibre-direction compression strength performance using HM fibres in a way that will enhance microstructural stability. The compressive strength of various fibre resin combinations was found to have increased with the increase of the shear modulus to axial modulus ratio of the composite system. Thus, it is noteworthy that from the observation in the experiment, hybridising carbon fibre with different moduli can achieve the anticipated compressive strength of the composite.\u003c/p\u003e \u003cp\u003eFrom the past literature, different composites with various off-axis angles have shown potential in terms of mechanical properties [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e],[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e],[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e],[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. However, there are no comprehensive reviews on the oil palm biomass reinforced composites with factors such as fibre orientation, fibre volume fraction and sizes of different fillers affecting the mechanical performance, primarily the compressive strength. The off-axis plies of the laminate exhibited lower compressive strength due to fibres slipping away from resins, and more voidage was found [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e],[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e],[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e],[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. There are also agglomeration issues that arose when a single filler particulate was introduced to the resin as a reinforcing filler [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Therefore, there is a clear research gap to evaluate the compressive behaviour of the hybrid composite by varying the fibre orientation and at the same time incorporating the secondary reinforcement fillers with different sizes (micro and nano) that are expected to minimise the agglomeration problem and further improve the compressive strength. The results of this research would be an added contribution to solving the low-compressive problems in producing composites for structural applications. In addition, this research project does not pose ethical issues.\u003c/p\u003e"},{"header":"3 Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Experimental Procedure\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarises the experimental flow chart. Oil palm empty fruit bunch (OPEFB) fibres were collected from the local oil palm mill (SOPB Sdn. Bhd.). The fruit bunch were then cleaned to remove mud and grease before being immersed in 5% alkaline solution (NaOH) to remove substances such as lignin, pectin and hemicellulose. After 24 hours of alkalinisation, the OPEFB fibres were rinsed with distilled water to remove the remaining sodium hydroxide before being dried in the oven for 24 hours. The OPEFB fibres were then combed using a special combing tool for straightening purposes, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cem\u003e(a).\u003c/em\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe fabrication process was done using the vacuum-assisted resin transfer moulding method (VARTM). Before starting the fabrication process, the vacuum cavity must be prepared. Once the mould-releasing wax was spread evenly on the plate surface, the fibres were then aligned on the plate surface and sealed to form the vacuum cavity. Appropriate usage of tacky tape was necessary to ensure a tightly secured seal to prevent air leakages. The leak test was performed for 15 minutes to ensure no air leakages. According to the high-performance industrial application, the vacuum state needs to be maintained, and the maximum acceptable leak rate must be controlled at 3\u0026ndash;5 mBar (0.08\u0026ndash;0.15 Hg) per minute [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMiracast 1517 A epoxy resin, and its hardener, Miracast 1517 B were poured into two separate cups. 150 g of epoxy was measured using the weighing balance and poured into a new cup. The disposable cup containing epoxy was then filled with 45 g of hardener. The mixture was manually stirred at about 120 rpm for 5 minutes. The resin transfer to the mould was facilitated using the injection pressure vacuum pump. Subsequently, the specimens were allowed to dry at room temperature and undergo a 24-hour curing process. The samples were removed from the vacuum seal and subjected to a post-curing procedure at 90\u0026deg;C for 2 hours. The specimens were then cut into cubical sizes according to the desired fibre orientation following ASTM D695 using the Lartone lapidary saw, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cem\u003e(b).\u003c/em\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe designation for the unidirectional oil palm empty fruit bunch (OPEFB) with different fibre orientations is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\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\u003eDesignation for unidirectional oil palm empty fruit bunch (OPEFB) series\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDesignated Name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eType of filler\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFibre Orientation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAverage total filler weight percentage (wt%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e45\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e60\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPEFB 90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOPEFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026asymp;\u0026thinsp;32 wt%\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=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Compression Test\u003c/h2\u003e \u003cp\u003eThe mechanical properties of the composite specimens under compression loading were investigated using the Instron 5982 universal testing machine (UTM) shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Specimens for compression testing were evaluated according to the ASTM standard listed above using a 100 kN load cell and a crosshead rate of 1.3 mm min-1. Measurements of the width and thickness of the specimens are obtained using a digital micrometre. The standard shape of the specimen is cubical, with dimensions of 25.4 \u0026times; 12.7 \u0026times; 12.7 mm. Each composite composition was tested with ten specimens, for which the mean and standard deviations are presented in this work.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Optical Microscope \u0026amp; Scanning Electron Microscope (SEM)\u003c/h2\u003e \u003cp\u003eThe microstructure analysis of the OPEFB-fibre composite specimens was conducted by examining the fracture surface of the composite using an optical microscope. The Thermo Scientific Quattro S scanning electron microscope and Olympus optical microscope were used for the observation of microstructural analysis, which includes the surface morphology, structure, and topology of the specimens. Each equipment offers information on failure criteria and types of failure of the fractured surface in the composite specimens, and identification of fibre fracture surface conditions with different magnifications.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Results","content":"\u003cp\u003eThis section presents the compressive strength of OPEFB fibre-reinforced composites, supported by failure behaviour observations and FTIR spectrum analysis.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Experimental Procedure\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the compressive strength of the unidirectional OPEFB series with different fibre orientation angles ranging from 0\u0026deg; to 90\u0026deg;. The weight percentage of OPEFB fibres used is approximately 32 wt%. OPEFB 15 composite offers the highest compressive strength, 75.66 MPa, a 6.5% improvement compared to the pure epoxy samples without OPEFB reinforcement at 71 MPa. It is followed by OPEFB 0, which exhibited a relatively good but slightly lower compressive strength performance of 69.77 MPa. The lowest compressive strength was observed in the largest off-axis value of the OPEFB 90 composite, which had a compressive strength of 39.52 MPa. A steady decline could be observed at off-axis angles of 30\u0026deg; onwards to 90\u0026deg;. The results shown are in line with the investigation conducted by the previous research, where OPEFB fibre composites were shown to have lower compressive strength at larger fibre orientation angles compared to samples of smaller fibre orientation angles [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e],[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e],[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The fibre content in all specimens was maintained at approximately 32 wt%. However, due to the nature of the fabrication process, achieving an exact weight percentage is not feasible. This is primarily because the volume of resin that flows into the cavity during the VARTM process cannot be precisely controlled prior to fabrication. As a result, the actual fibre content varied slightly, ranging between 30\u0026ndash;33 wt%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is noticeable from the bar chart, the compressive strength reduced, as the fibre orientation increased except for OPEFB 15. In typical situations, the specimens with fibres aligned (0\u0026deg;) would possess the highest strength properties as the longitudinal fibres placed in the load's direction could directly absorb, transfer, and distribute the load uniformly throughout the cross-section. However, in this study, the OPEFB 0 composite possessed slightly lower compressive strength than the OPEFB 15 composite. This could be caused by the arrangement of fibres in these specimens. In natural fibre composite, the reinforcing fibres act as the primary load-carrying component, while the matrix functions as a binder that binds with fibres and transfers loads between. The arrangement of fibres in OPEFB 0 was aligned along the load direction, causing the fibre to carry most of the load while the matrix played a relatively minor role in load transfer. Therefore, fibres experiencing heavy loads would form localised stress concentrations leading to premature failure caused by fibre fracture or buckling. For OPEFB 15, fibres were positioned at 15\u0026deg; angle, they were not perfectly aligned with the load direction. The slight deviation from the on-axis caused the fibres to experience less load-bearing burden, but still primarily aligned with the load. Compression forces tend to act more evenly across the composite, making the matrix play a crucial role in supporting the loads. The matrix functions more as a load-carrier by sharing the load with the fibres, resulting in a more favourable stress distribution or interaction between fibres and matrix. Therefore, 15\u0026deg; orientation specimens achieved a balance where fibres still contributed to strength but were not as dominant as those found in 0\u0026deg; orientation specimens while the matrix\u0026rsquo;s strength assisted in supporting the load more effectively.\u003c/p\u003e \u003cp\u003eThe results were aligned with the findings of Oh \u003cem\u003eet. al\u003c/em\u003e [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] where the bearing strength of 15\u0026ordm; fibre orientation specimens was found to be 7.56% higher compared to those of 0\u0026ordm; orientation. The authors further elaborated on the load distribution as 0\u0026ordm; fibre orientation directly absorbs the applied load. However, when the fibre is positioned in the off-axis direction (15\u0026ordm;), the load is further decomposed into \u003cem\u003esinθ\u003c/em\u003e and \u003cem\u003ecosθ\u003c/em\u003e components, distributing the stress into longitudinal and transverse directions. This reduces stress concentration and the occurrence and propagation of damage. Therefore, specimen (0\u0026ordm;) experiences initial fracture comparatively faster than specimen (15\u0026ordm;). According to Akhyar \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], longer fibre length imparts higher strength in the direction of the fibre. When the composite is cut to different orientation angles, i.e., (0\u0026deg;, 15\u0026deg;, 30\u0026deg;), each sample's fibre length would differ. For instance, the specimens with a 15\u0026deg; orientation would have their fibre length longer than those of 0\u0026deg; due to the fibres being slightly tilted; thus, the compressive strength of OPEFB 15 was higher than OPEFB 0.\u003c/p\u003e \u003cp\u003eAnother possible reason for this scenario could be due to the fibre misalignment generated during the fabrication of the fibre composites. The fibre misalignment is a manufacturing defect created by fibre movement in the matrix. When the vacuum pump was turned on during the VARTM process, it might have influenced the compressive strength of the fibre composites [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e],[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. In general, the variation of the fibre misalignment is more significant in the hand-made fibre composites that require minimal involvement of equipment, and this is highly likely to be responsible for the reduction of the compressive strength in the OPEFB 0 composite samples [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe compressive strength of the hybrid composite was noticed to exhibit a decreasing trend at larger fibre angles, specifically from 30\u0026deg; onwards. The possible explanation for this scenario is that at larger fibre angles, i.e., transverse compression (fibre direction at 90\u0026deg;), the load-bearing capacity of off-axis specimens deteriorates due to the fact that the fibres start slipping as they are subjected to the load. The fibres mainly resist transverse stresses, making the fibre-matrix interface a critical weak point. The functional effectiveness of the epoxy matrix to act as the binder material to hold fibres in position while transferring external loads to internal reinforcement was reduced. This will lead to a strength reduction of the composite at higher fibre angles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Failure mode analysis for OPEFB reinforced composite of various fibre orientation\u003c/h2\u003e \u003cp\u003eTo enhance the understanding of failure behaviour and its relation to compressive strength, the surfaces of the specimens were analysed using the optical microscope. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e depict images taken from the optical microscope that illustrate the fracture surfaces of the OPEFB composites; random fibre fractures are observed, likely resulting from excessive bending during buckling post-matrix yielding. Additionally, a clean fibre surface signifies significant failure at the fibre-matrix interface.\u003c/p\u003e \u003cp\u003eThe fracture surface of OPEFB 0 specimens shows multiple fibre breaks and localised rotation of broken fibres. These fibre fractures indicate that fibre microbuckling might have occurred in these unidirectional composites. The mode of failure in the specimen subjected to longitudinal compression (\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg;) was a mixed failure mode of fibre splitting/fracture with minimal fibre kinking along the fibre direction, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cem\u003e(a).\u003c/em\u003e In contrast, the fracture surface of OPEFB 15 shows multiple fibre kinking, with no obvious fibre fracture. The fibre kink failure mode was the dominant failure mode in specimens subjected to 15\u0026deg; off-axis fibres. Typically, unidirectional laminates tend to experience shear mode failure when subjected to off-axis compressive loading. However, under compressive loads applied in the fibre direction or in the case of OPEFB 15, where fibres are still primarily aligned with the load, failure commonly occurs due to micro-buckling or kinking of fibres within a localised region. Due to the randomly oriented nature of the fibres in the composite, this kind of failure is only found on the fibres oriented along the loading axis of the specimen. Comparing the fracture surface of both OPEFB 0 and OPEFB 15, the 0\u0026deg; orientation specimens showed more localised and pronounced shear bands, which indicates early fibre kinking. The cracks and damage propagate along the fibre direction, which leads to a more sudden and catastrophic splitting failure. Meanwhile, from Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u003cem\u003e(b)\u003c/em\u003e, the 15\u0026deg; orientation specimen showed more distributed shear bands due to the slight fibre misalignment, causing composite failure to occur progressively in a controlled manner. The cracks also deflected more due to the off-axis fibres, leading to an increase in fracture resistance. The angled fibres are believed to have delayed the fibre-kinking process, thus improving the load-bearing capacity as more force is required to initiate fibre microbuckling. The results from the previous section also reflected that OPEFB 15 exhibited a slightly higher compressive strength than OPEFB 0. According to the longitudinal compression and smaller off-axis angles (i.e. \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg; and 15\u0026deg;), failure modes were mostly the combined in-plane and out-of-plane kink modes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe specimens that have fibre orientation of different axes show a cleaner failure. The off-axis compressive strength is also found to be affected by the dominant mode of failure. In the case of the OPEFB 30, OPEFB 45, OPEFB 60, OPEFB 75, and OPEFB 90 specimens, there seems to be considerable shear failure together with matrix tearing or cracking. In larger off-axis angles (i.e. \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg;), shear failure of the matrix seems to be a dominant failure mode. Notably, the specimens that experienced fibre kinking or micro buckling had higher strength compared to those that failed in a matrix-dominated mode. This suggests that friction on the contact surfaces was not eliminated during the testing of these two specimens, and thus, lateral constraint delayed the onset of matrix cracking.\u003c/p\u003e \u003cp\u003eThe specimens that experienced the combination of in-plane and out-of-plane kinking modes resulted in higher compressive strength compared to those of in-plane and out-of-plane shear modes. The increased compressive strength observed at a 15\u0026deg; fibre orientation is attributed to this kinking mechanism, whereas at angles greater than 30\u0026deg;, where shear modes dominate, compressive strength deteriorates. From the study of Kawai and Saito [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], these findings indicate that, if governed by typical compressive failure modes, the off-axis compressive strength tends to surpass the off-axis tensile strength across a variety of fibre orientations. When the off-axis angle exceeds 30\u0026deg;, the matrix cracking is aligned with the fibre orientation, and the primary failure mechanism typically occurs at the specimen\u0026rsquo;s centre. For specimens with off-axis angles of 45\u0026deg; and 60\u0026deg;, the fracture plane is nearly perpendicular to the specimen surface, which indicates that matrix failure is mainly caused by in-plane shear. Conversely, for specimens with larger off-axis angles, such as 75\u0026deg; and 90\u0026deg;, the fracture surface is observed as inclined, which signifies a predominant influence of transverse compression where fibres are mainly resisting transverse stresses, making the fibre-matrix interface a critical weak point. From Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u003cem\u003e(a)\u003c/em\u003e, the fibres appear to have separated from the surrounding matrix, which suggests a weak fibre-matrix interface. This is also characteristic of interfacial failure, where the bond between the fibre and matrix is compromised. From Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u003cem\u003e(b)\u003c/em\u003e, the failure is dominated by poor fibre-matrix adhesion, where resin/matrix appears to be fractured, leading to cracks running along the matrix-rich regions.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the macroscopic failure modes in off-axis compression for the specimens with \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg; to 90\u0026deg;, respectively. In cases of specimens with on-axis longitudinal compression and small off-axis angles, particularly 0\u0026deg; and 15\u0026deg; specimens, failure was also prominently influenced by fibre kinking induced by fibre micro buckling. These images also demonstrate that the specimens with the off-axis fibre orientations \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30\u0026deg;, 45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg; failed along the fibre direction in a combined in-plane and out-of-plane matrix shear mode. For fibre orientations \u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15\u0026deg; (OPEFB 15), only a single mode of failure was observed. The fracture surface was parallel with the fibres, and it was appreciably inclined from the through-the-thickness direction of the specimen, with no premature end collapse or splitting observed along the fibre direction. In contrast, the longitudinal compression (\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg;, OPEFB 0) specimens experienced failure primarily due to both fibre splitting/ fracture and fibre kinking mode. This can be largely attributed to the direction of compression load application and the cross-sectional dimensions. The close-up view showcasing the presence of kink bands and fibres splitting in OPEFB 0 specimens using the SEM is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA unidirectional composite behaves almost like a linear elastic material when subjected to longitudinal tensile/compressive or transverse tensile loads. However, when exposed to transverse compressive loads, a unidirectional composite exhibits some degree of nonlinearity. Nevertheless, this nonlinearity is primarily attributed to matrix plasticity rather than interface damage [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe highest and lowest compressive strengths are found in OPEFB 15 and OPEFB 90, respectively. Therefore, the load-deformation curves of these two specimens were compared. From Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the uniaxial compressive load-deformation curves of both OPEFB fibre orientations of 90\u0026deg; (OPEFB 90) and 15\u0026deg; (OPEFB 15) are shown to be mostly single-peak curves. Peak deformations of OPEFB 90 specimens are up to 1\u0026ndash;2 times as large as those of the OPEFB 15, thus showing that the deformation strength of OPEFB 90 specimens is higher. Fibre orientation has affected the strength of specimens and, at the same time, caused an influence on the deformation ability. The OPEFB 15 specimens were notably influenced by the material properties aligned with the fibre direction, as evidenced by the graph in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, which depicts minimal non-linearity before failure. Consequently, the yield criterion was not met, resulting in a lack of ductility. Conversely, the experimental results for the OPEFB 90 specimens exhibited a more nonlinear behaviour, suggesting a potential for higher ductility. Although OPEFB 90 possessed much lower compressive strength, the deformation ability was still better than OPEFB 15, which possessed excellent compressive strength. Therefore, it is worth further investigating the ductility of the specimens, whether they still have good integrity after compressive damage and the ability to possess more residual bearing capacity during larger compressive deformations.\u003c/p\u003e \u003cp\u003eFor larger off-axis angles, compressive failure occurred predominantly in a single mode, combined in-plane and out-of-plane shear mode. Consequently, nearly identical stress-strain relationships were observed across different specimens for each of these fibre orientations. Notably, for fibre orientations such as (\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg;), the off-axis flow stress level in compression within the nonlinear range was significantly higher compared to smaller off-axis angles. This indicates that higher external stress is consistently required to induce off-axis nonlinear compressive deformation for these fibre orientations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Fourier Transform Infrared (FTIR)\u003c/h2\u003e \u003cp\u003eThe FTIR analysis of 0\u0026deg;, 15\u0026deg;, and 90\u0026deg; OPEFB epoxy composites provides insight into the fibre-matrix interactions and epoxy crosslinking efficiency is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. While differences between orientations are observed, the variations in chemical bonding are rather moderate than drastic. There are no significant differences in terms of compound changes and chemical bonding changes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThere are two main transmittance regions at low and high wavenumbers between 500\u0026ndash;1800 cm⁻\u0026sup1; and 2700\u0026ndash;3500 cm⁻\u0026sup1;, respectively, aligned with the data reported previously [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e],[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. In the FTIR analysis of all three specimens, a broad absorption band was observed at 3325 cm⁻\u0026sup1; indicating the presence of O-H stretching due to cellulose [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. OPEFB 15 represented by 15\u0026deg; OPEFB\u0026thinsp;+\u0026thinsp;epoxy in this graph, have exhibited lower transmittance at this peak as comparison to the other two specimens, OPEFB 0 and OPEFB 90, represented by OPEFB 0\u0026deg; + epoxy and OPEFB 90\u0026deg; + epoxy. The 15\u0026deg; specimens show the lowest transmittance percentage, which indicates the maximum absorption, followed by the 0\u0026deg; and 90\u0026deg; specimens. Interestingly, the findings at this peak also reflect the higher compressive strength possessed by OPEFB 15.\u003c/p\u003e \u003cp\u003eWhile at the peak near 1700 cm⁻\u0026sup1;, corresponding to the C\u0026thinsp;=\u0026thinsp;O (carbonyl) stretching, was also found in all three specimens of different orientations. The peak was found to be slightly more shifted at 15\u0026deg; (OPEFB 15), meaning more chemical interaction might have occurred. The OPEFB fibre surface might be more exposed or react better with the epoxy functional group in OPEFB 15 specimens. This might be due to the longer fibre in the specimens compared to OPEFB 0 and OPEFB 90. The 15\u0026deg; composite also showed a slight reduction in transmittance compared to the specimens of 0\u0026deg; and 90\u0026deg;, though the differences are not substantial enough to suggest a major structural change.\u003c/p\u003e \u003cp\u003eIn the 1000\u0026ndash;1250 cm⁻\u0026sup1; region, which signifies the C-O-C stretching (cellulose bond), confirming the ether linkages in the epoxy network and its cross-linked structure[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. At wavenumber 1029 cm⁻\u0026sup1;, the OPEFB 15 exhibited a slightly increased peak intensity, followed by OPEFB 0 and OPEFB 90, which may imply better epoxy crosslinking for OPEFB 15 as there are more reacted epoxy. However, all the other specimens, OPEFB 0 and OPEFB 90, also showed the occurrence of these key functional groups, which signifies that adhesion is present across all specimens with only moderate variations. OPEFB 15 also has the lowest transmittance in this region.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eAs concerns about the depletion of natural resources continue to rise, there is a growing urge to utilise renewable resources like oil palm empty fruit bunch (OPEFB) in composite manufacturing.\u0026nbsp;Thus, it can be expected that the upshot of this research will enlighten the upliftment of the compressive properties of natural fibre-reinforced composite.\u003c/p\u003e\n\u003cp\u003eThe scientific significance of the research includes:\u0026nbsp;\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eIt is hypothesised that the study of different fibre orientations would help to identify the effective parameter of the composite with improved compressive properties. \u0026nbsp;From different fibre orientations of OPEFB fibres being reinforced in the epoxy, it was found that OPEFB 15 (\u003cem\u003eθ\u003c/em\u003e =15°) showed the most consistent and highest compressive strength properties, even compared to the pure epoxy specimens. The lowest compressive strength was possessed by the OPEFB 90 specimens (\u003cem\u003eθ\u003c/em\u003e =90°). The main reason for the strength to deteriorate is that the transverse compression does not have the load-bearing capability as the load direction is perpendicular to the fibre’s direction. It is also worth highlighting that although the composite has low compressive properties, the deformation ability is higher than those with higher compressive properties.\u003c/li\u003e\n\u003c/ol\u003e\n\u003col start=\"2\"\u003e\n \u003cli\u003eThe failure behaviour of these composites could be examined by analysing the fracture surface of specimens. The type of failure modes and behaviour of composites strongly differ according to their relative fibre orientations. OPEFB 15 with the highest compressive strength exhibited kink-band failure, which is induced by fibre microbuckling, while the lowest compressive strength, OPEFB 90, showed matrix tearing/ cracking failure.\u0026nbsp;\u003c/li\u003e\n\u003c/ol\u003e\n\u003col start=\"3\"\u003e\n \u003cli\u003eThe FTIR analysis also confirmed that OPEFB 15 exhibited the strongest fibre-matrix interaction, best curing, and overall improved bonding performance.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFong Ai Ling and Amanda Mu acknowledge the Curtin Malaysia Postgraduate Research Scholarship (CMPRS) from Curtin Malaysia Graduate School. Fong Ai Ling would also like to thank the School of Pre-U and Continuing Education (SPACE) from Curtin Malaysia. Furthermore, the authors would like to express their gratitude to Curtin University Australia, Glasgow Caledonian University, and University Kuala Lumpur (UniKL).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFong Ai Ling: Investigation, Visualisation, Writing( Original Draft), Writing (Review \u0026amp; Editing.\u003c/p\u003e\n\u003cp\u003eAmanda Mu: \u0026nbsp; \u0026nbsp; \u0026nbsp; Conceptualisation, Investigation, Visualisation, Writing\u0026ndash; Review \u0026amp; \u0026nbsp; \u0026nbsp;Editing. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLau Shiew Wei \u0026amp; Sujan Debnath: Conceptualisation,\u0026nbsp;Visualisation, Writing\u0026ndash; Review \u0026amp; Editing, Supervision.\u003c/p\u003e\n\u003cp\u003eMahmood Anwar, Ian J. Davies \u0026amp; Mahzan Bin Johar: Methodology, Language checking, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not received funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData generated or analyzed in this study can be obtained from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from all authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eI. 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Text.\u003c/em\u003e, vol. 55, p. 15280837241313217, Apr. 2025, doi: 10.1177/15280837241313217.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"discover-mechanical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"discmecheng","sideBox":"Learn more about [Discover Mechanical Engineering](https://www.springer.com/journal/44245)","snPcode":"44245","submissionUrl":"https://submission.nature.com/new-submission/44245/3","title":"Discover Mechanical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Hybrid Composite Materials, Oil Palm Empty Fruit Bunch, Fibre Orientation, Compressive Strength","lastPublishedDoi":"10.21203/rs.3.rs-8323000/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8323000/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper aims to develop and study the off-axis compression behaviour in natural fibre polymer composites. A study was conducted to investigate the effect of various fibre orientations on the compressive properties of the natural fibre composite. The primary phase of the composite is epoxy resin, while the secondary phase (filler) is the oil palm empty fruit bunch (OPEFB) fibres. The OPEFB-fibre composites were prepared using the vacuum-assisted resin transfer moulding (VARTM) technique. Compression test according to ASTM D695, scanning electron microscope (SEM), and Fourier transform infrared (FTIR) analysis were conducted on the specimens. The compressive strength results indicate the anisotropic behaviour of the polymer composite due to different fibre orientations, with the highest compressive strength found in 15\u0026deg; specimens. The observed failure modes of the composites were analysed and found to be consistent with the compressive strength results through both the SEM and the optical microscope images.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e","manuscriptTitle":"Experimental study and failure mode analysis of off-axis compression behaviour in natural fibre polymer composite","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-22 09:26:24","doi":"10.21203/rs.3.rs-8323000/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-08T08:30:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-04T06:44:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-29T19:29:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"58238540398266171043796006309541822799","date":"2025-12-25T12:31:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-22T10:21:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"229200919161591690493535109357706712266","date":"2025-12-21T15:30:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"63565604338983536337752173006180052390","date":"2025-12-16T04:34:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-16T02:37:25+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-12T07:09:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-12T07:07:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Mechanical Engineering","date":"2025-12-10T04:38:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-mechanical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"discmecheng","sideBox":"Learn more about [Discover Mechanical Engineering](https://www.springer.com/journal/44245)","snPcode":"44245","submissionUrl":"https://submission.nature.com/new-submission/44245/3","title":"Discover Mechanical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b2b1f246-199d-4a73-84c7-3ba7271ec938","owner":[],"postedDate":"December 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-03T09:40:06+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-22 09:26:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8323000","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8323000","identity":"rs-8323000","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}