Progressive failure analysis of carbon-fibre/epoxy composites laminates to study the effect of stitch densities under in-plane tensile loading

Through thickness reinforced stitched laminates with different stitch densities (0.11 and 0.028 mm(-2)) were studied in order to analyse effects on laminate behaviour, under in-plane tensile loading based on continuum mechanics. Multi-layered stitched laminates with the stacking sequence [+45/90/-45/0(2)/+45/90(2)/-45/0](s) were modelled on a lamina-wise basis to analyse the macroscopic damage and local stress-strain constitutive behaviour. Interfaces between lamina and stitch yarns were assumed to be perfectly glued and were modelled by the contact capability. Discretisation procedures using the principle of virtual work were applied in addition to discretisation of the contact traction. Progressive failure analysis with Puck's failure criteria was conducted to characterise the failure behaviour of the laminate. This analysis showed that reinforcement density is one of the key factors affecting strength, stiffness and crack propagation in composite laminates. By suppressing the damage initiation, densely stitched laminates showed 15.2% higher in-plane stiffness than moderately stitched laminates. The results obtained by the finite element technique are consistent with the experimental results.