Adaption of a Material Model and Development of a Stochastic Failure Criterion for Ceramic Matrix Composite Structures

Abstract

Ceramic matrix composites (CMCs) show high thermal resistance combined with damage tolerance and non-brittle failure. Therefore they are suitable for mechanically loaded components under high temperatures. The introduction of oxide CMCs as material for combustion chambers of stationary gas turbines is a subject of current research. For the dimensioning of components, the adaption of existing simulation and calculation methods to CMC materials is required. This includes the development of a failure criterion ensuring high reliability of components against failure under consideration of the scatter in material strength.

The material investigated in this work is a wound oxide CMC with a defined fiber orientation and highly porous matrix. Due to manufacturing conditions, macroscopic pores with random orientation, location and size are present in the composite. Since failure is assumed to be caused by these pores, a statistical investigation of strength is performed, following the Weibull Theory.

A number of tensile tests were evaluated and compared with results of finite element simulations (ANSYS). By application of an optimization tool (optiSlang), the parameters of different orthotropic material models were determined. An anisotropic Weibull criterion was set up and adapted to the results of the tensile tests. Thus the non-linear deformation behavior as well as the specimen’s scatter in strength could be reproduced. The adapted material model and failure criterion were validated by further experiments, e.g. three point bending tests, which showed good agreement between simulated and experimental results. Moreover the failure probability of a thermally loaded combustion chamber was investigated to demonstrate the applicability in industrial context.