Colloquia

Summary

Ceramic Matrix Composite (CMC) consists of ceramic fibres embedded in a ceramic matrix. The material has favourable mechanical properties in high-temperature, corrosive environments. It features applications in jet or gas turbines, for example. By embedding fibres, the ability of the material to resist fracture is enhanced. Mechanisms such as fibre bridging ensure the load can be sustained, and deflection of the crack along the fibre coating ensures the fibre remains intact.

To improve material and structural characteristics, often extensive testing is required. This can be both expensive and time exhaustive. Therefore, there is a need to develop models to simulate the material behaviour numerically. In this study, modelling the fracture behaviour transverse to the fibre was considered with the embedded strong discontinuity approach. A custom finite element is implemented and model verification is performed. Next, the method's performance is verified to simulate the crack propagation through a representative volume element (RVE) of a fibre, and multiple fibres embedded in a ceramic matrix. The model was implemented in a standard finite element solver, to compute the augmented equations by the embedded discontinuity. Crack propagation was captured without external crack-tracking algorithms. Computations were performed on a personal computer with reasonable speed.

Initially, the model was successfully validated with several numerical examples. Next to that, the fracture behaviour of the heterogeneous CMC was simulated. Crack deflection through the coating could be captured, as reported by other authors. Kinking of the crack path between coating and matrix, and coalescence of multiple cracks were simulated. The use of higher fracture energies was required to preserve convergence to the solution, and the final loss of stiffness of the CMC could not be simulated due to global stress locking. The results were not correct as interlayer surface effects were omitted. Therefore, it is recommended to include the effects, and expand the model to three-dimensional domain to account for out-of-plane effects. Expansion of the kinematic model and numerical issues should be solved to obtain better results.