Meso-scale finite element modelling of biaxial non-crimp-fabric composites under compression

Non-crimp-fabric (NCF) reinforced composites have been receiving attention in the composite market due to their cost-effectiveness and excellent mechanical performance. However, compared to traditional unidirectional laminates (UD), NCF composites have different mechanical behaviours due to their heterogeneous internal structures. The influence of the internal structure of biaxial NCF composites on compressive behaviour was therefore investigated in this study. The representative volume element (RVE) method was adopted to establish finite element (FE) models for biaxial NCF composites at the micro- and meso‑scale. Micro-scale models developed at fibre/matrix level could provide homogenised compressive properties of 0° and 90° tows, while meso‑scale repeated unit cell (RUC) models developed at tow/resin-rich area level could predict homogenised compressive behaviours of biaxial NCF composites. Finally, the homogenised meso‑RUC results were employed in the macro-scale FE model to validate the test result. The novelty lies in developing RUC models to comprehensively investigate key parameters at the micro- and meso‑scale controlling the overall compressive strength, including matrix strength, layup sequence, tow waviness, tow placement, interfacial strength, and out-of-plane shear stress. Another novelty is to explain the differences in compressive strengths between the RUC model and the test result. These models form a multiscale framework for biaxial NCF composites, which could contribute to an analysis tool for NCF material design. The FE results by this multiscale framework indicated that the misaligned resin-rich areas could contribute to the higher compressive strength. Increasing tow waviness could change the failure mode from fibre crushing to fibre kinking failure, while matrix properties, interfacial strength, and fibre waviness were the key factors influencing compressive strength. The conclusion can further guide the development of NCF composites with optimal compressive strength.