Numerical simulation and R-curves computation of CFRP compact tension tests using the discrete ply model

Abstract

Efficient and accurate failure modelling of composite materials is crucial due to their extensive use in the industry. Specifically, simulating translaminar failure, such as Compact Tension (CT) tests using finite element analysis, has proven particularly challenging. This study applies the mesoscale finite element Discrete Ply Model (DPM) to the case of unidirectional carbon fibre CT tests. The stacking sequence employed is [45/-45/[0/90]₄]_s. This configuration has demonstrated significant experimental advantages, such as reduced specimen buckling and minimal shear matrix plasticity. However, it also displays a more complex combination of failure modes, including extensive delamination during crack propagation. This may result in inaccurate computation of the critical Strain Energy Release Rate (SERR), thus requiring new analysis methods. In the DPM, matrix cracking and delamination are explicitly represented. Failure modes such as fibre failure in tension/compression, shear damage and crushing are modelled within the behaviour volume elements. A new law that accounts for the increase in compressive failure strain in the presence of planar or strain gradients is proposed and shown to be crucial to the correct complete computation of the failure scenario. This approach shows relevant numerical and experimental correlation, both for the force-displacement curves and for the critical SERR computed with the compliance method. To address the issue of the complex CT failure scenario, the model estimates the energy dissipated by each failure mode. A numerical R-curve is also computed directly from these energies, allowing the discussion of the different ways of computing R-curves, numerically and experimentally.