Adaption of a material model and development of a stochastic failure criterion for ceramic matrix composite structures

Kurzfassung

Ceramic matrix composites (CMCs) show high thermal resistance combined with damage tolerance and non-brittle failure. Therefore, they are suitable for mechanically loaded components at high temperatures. For dimensioning of components, an adaption of existing simulation and calculation methods for CMC materials is required. The material investigated in this work is a wound oxide CMC with a defined fiber orientation and a highly porous matrix. Due to manufacturing conditions, randomly distributed macroscopic pores are present in the composite. Since failure is initiated by these pores, a statistical investigation of strength is performed based on the weakest link theory. Several series of tensile tests were performed to reveal the relation between stress and strain and obtain their ultimate values. The application of two statistical criteria showed that fracture strains are well represented by Weibull distributions. The tensile tests were compared with results of finite element simulations, using the simulation software ANSYS. An anisotropic Weibull criterion was set up and adapted to the results of the tensile tests. Hereby, the anisotropic nonlinear deformation behavior as well as the scatter of failure strain could be reproduced by numerical simulations. The adapted material model and failure criterion were validated by further experiments and exemplified by application in a reliability analysis of a notional flame tube.