MULTI-SCALE ANALYSIS OF MECHANICAL PROPERTIES OF THREE-DIMENSIONAL BRAIDED CERAMIC MATRIX COMPOSITES WITH PORE DEFECTS

The multi-scale finite element model is developed to investigate the strength and damage behaviour of 3D braided composites with pore defects. The pore defects inside the composites are inspected and measured using CT scan. Based on the void data, the trans-scale numerical models are established, including the interface. Damage evolution under longitudinal tensile loading was evaluated. The effective properties are transferred from the fibre bundle scale to the mesoscale using the machine learning-based clustering method and further, the finite element model with pore defects is used to predict the macroscopic mechanical properties. Periodical boundary conditions are applied to the multiscale FE models by the coupling and constraint equation, with defining commands available in Abaqus. It has been shown that the failure modes of yarn damage, matrix cracking and interface debonding are recognized and correspond well with the final failure morphology of the sample. The damage appears around the pore defects and then develops to the weak region in the matrix. Pore defects of the composites have a significant influence on the tensile behaviour of the composite, which is captured by the proposed multi-scale damage model. The porosity has a greater influence on the strength of the composite, in which the pore content increases by 10 % and the strength of the composite decreases 12 % approximatively. The validated models can be further used to predict the mechanical property of 3D braided composites with pore defects.