Investigation of the Effect of Tufts Contribution on the In-Plane Mechanical Properties of Flax Fibre Reinforced Green Biocomposite

Abstract Traditional laminated composites have fibres oriented only in the in-plane of the laminate due to their manufacturing process, and are therefore very susceptible to transverse cracking and delamination from out-of-plane actions. Delamination can considerably reduce the load bearing capacity of a structure hence several reinforcement solutions, based on the principle to add out-of-plane reinforcement to the 2D fabric, have been explored to enhance the delamination resistance. However, the usual textile technologies for Z-reinforcement such as weaving, knitting, stitching, z-pinning, and tufting generates perturbations that may alter the in-plane mechanical properties. Although tufting is a single needle and single thread based one side stitching (OSS) technique which can incorporate almost tension free through the thickness reinforcement in a material, various types of microstructural defects may be created during the manufacturing process and lead to a degradation of the in-plane properties of the composite. Moreover, due to awareness in environmental concerns, the development and use of eco-friendly biocomposites to replace synthetic ones has been increasing. This research work investigates the effect on in plane mechanical properties of adding through the thickness reinforcement (TTR) by tufting in a flax based composite laminate to improve the transversal strength. The glass fibre tufted laminates of 550 g/m2 flax fibre were moulded using a 38% biobased thermoset resin by vacuum bag resin transfer moulding (VBRTM). The tufted and un-tufted in-plane mechanical properties of green biocomposite were determined in tension, compression and shear in accordance with ASTM 3039, ASTM D7137 and EN ISO 14130, using universal INSTRON 1186 and MTS 20M testing machines. The quantification of the in-plane mechanical properties results established a reduction of the in plane tensile mechanical properties, due to tufting, whereas the reduction effects are marginal in compression. As expected, the glass tufts strength the connection between core and skin of the composite so that the interlaminar shear strength, deduced from flexural tests with small span-to-thickness ratio, is increased, Thanks to Digital Image Correlation (DIC) performed during shear tests an increase in interlaminar shear modulus is highlighted.