Computational modelling of failure mechanisms in fibre metal laminates

In this thesis, a numerical framework is developed for predicting the mechanical behaviour and failure mechanisms of Fibre Metal Laminates (FMLs). Modelling the behaviour of these materials is challenging due to the diverse material behaviours of its constituents, combined with the heterogeneous nature of composites, which result in various failure modes. In order to accurately predict the damage process of these materials, a 3D damage model is required. Therefore, a comprehensive 3D finite element model incorporating various material models, failure criteria and damage evolution laws has been developed. In this model, a user-defined subroutine is developed in Fortran and linked with the Finite Element (FE) solver Abaqus/Explicit. Through this subroutine, physically verified theories are utilized for predicting the onset of damage in composites. A criterion for predicting the fracture plane at the onset of failure in composites is implemented where the efficiency of the subroutine is enhanced by implementing a fast search algorithm. The damage propagation is simulated with an evolution law, modified to align with the damage initiation criteria. Additionally, the crack paths are predicted by deleting the failed elements using volume-based criteria. The subroutine is validated by comparing the results of a simulated tensile test of CFRP with experimental data, which demonstrated excellent agreement between the stress-strain curves and reasonable prediction of the failure modes. The framework is applied for simulating two mechanical tests: the open-hole tensile test of GLARE and the flexural test of CARALL. In both studies, the conditions of the experimental setup were replicated in the FE models and the specimens were tested at both on-axis and off-axis fibre angle orientations. Mesh sensitivity studies were conducted to ensure the accuracy of the results and the predicted stress-strain curves showed overall excellent agreement with experimental data. Additionally, the studies highlighted the failure modes captured during the simulations, where the FE models successfully distinguished between fibre and matrix damage modes, plastic deformation and delamination.