Multiaxial characterization of cross-ply and quasi-isotropic flax bio-composites using a modified Arcan fixture and digital image correlation

This study investigates the mechanical behavior, stress–strain states and damage evolution of flax-fiber reinforced polymer composites under various loading angles using Arcan specimens with V-notches. Three stacking sequences, cross-ply [0/90]4s, quasi-isotropic [45/−45/0/90]2s, and angled cross-ply [45/−45]4s, were examined to assess their response to combined tension and shear loading at angles of 0°, 45°, and 90°. Digital Image Correlation (DIC) was employed to capture detailed strain fields and principal strain orientations, enabling direct comparison with numerical predictions from finite element modelling. Results show that the [45/−45]4s laminate exhibits superior shear load-bearing capacity due to the transformation of shear into tensile and compressive stresses within ±45° plies. Notch sensitivity varied significantly among laminates, with the [45/−45/0/90]2s configuration showing greater damage tolerance, a smaller strength drop at off-axis angles, and a reduced notch effect compared to cross-ply laminates. The study reveals complex strain localization patterns and fiber-matrix interactions influencing crack initiation and propagation. These findings enhance the understanding of anisotropic damage mechanisms in natural fiber composites and provide valuable insights for optimizing biocomposite layups in structural applications subjected to multiaxial stress–strain states.