Multiscale modelling of residual thermal stresses and off-axis bending in 3D braided composites

As the failure of three-dimensional (3D) braided ceramic matrix composites (CMCs) at the structural scale are inherently influenced by their complex braid architecture at the mesoscale, a multiscale modelling method is proposed to investigate the mechanical response and damage evolution of 3D braided CMCs under combined loads induced by off-axis bending. The measured load-displacement response from off-axis three-point bend tests on 3D braided CMCs specimens for different off-axis angles agreed well with the model predictions. The study has identified the sequence and extent of various modes of damage, such as yarn breakage, matrix cracking, and yarn stripping. The multiscale model is also employed to analyze residual thermal stresses and the flexural response of 3D braided CMCs at different temperatures. The results indicate that the stiffness of the composite increases with temperature and peaks around 1000 °C. Above this temperature, the weakening of matrix-fiber interfacial bonding and the accumulation of internal damage results in a gradual decrease in the elastic modulus, with significant reductions observed above 1500 °C. These findings provide insight into the design and optimization of 3D braided CMCs destined for use in high-temperature and complex service environments.