Development of a Stochastic Simulation Approach for High Temperature Components made of WHIPOX (oxide/oxide CMC)

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 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 WHIPOX, a wound oxide/oxide CMC with a defined fiber orientation and highly porous matrix. A number of tensile tests, performed at different temperature levels, were evaluated. The temperature-dependent deformation parameters of a modified orthotropic material model were determined from the experimental results and integrated in finite element simulations. Additionally, a failure criterion is required for component design. 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. Therefore, 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 by finite element simulation and post processing. 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.