Stress-strain response and thermal conductivity degradation of ceramic matrix composite fiber tows in 0-90° uni-directional and woven composites

The physical model for tow behavior, developed previously by the authors, is used to study the performance of two woven CMC laminates: a carbon fiber/carbon-SiC matrix (C/C-SiC) plain weave laminate - DLR-XT; and a carbon fiber- carbon matrix (C/C) 8-Harness Satin weave laminate - HITCO. For both materials, room temperature stress-strain curves and transverse thermal conductivity-strain curves are available from a previous experimental investigation; these curves have been used as benchmarks to assess the fidelity of the models. The tow model has first been used to develop relationships for 0°/90° uni-directional unit cells, and then adapted to cater for unit cells of the DLR-XT and HITCO woven composites. For both materials, acceptable predictions have been made of stress-strain behavior. Despite the thermal models being based on one-dimensional heat flow, within series-parallel elements, excellent predictions have been made of the degradation in transverse composite thermal conductivity with the composite strain. Furthermore, it has been confirmed that the effect of the degradation of transverse thermal conductivity is due to strain-driven growth of wake debonded cracks.