Notch-strength prediction of ceramic matrix composites using multi-scale continuum damage model

In-plane failure behavior of SiC/SiC Ceramic Matrix Composites (CMCs) containing notches of different shapes is studied using experiments and associated computational model. The experimental work consisted of room-temperature tensile tests on an 8-harness satin woven CMC material with three different notch geometries: (1) a through-thickness center hole, (2) a semi-circular notch on both edges, and (3) a rectangular slit on both edges. A multi-scale continuum damage mechanics model is used in conjunction with Finite Element Analysis (FEA) to predict the overall failure response of the notched specimens. The continuum damage model is based on reduced order homogenization theory with damage variables defined at the meso-scale (i.e., at the scale of tows and matrix in the representative volume element of the CMC), and furthermore, the model considers failure in each of the constituents via softening stress-strain response with appropriate fracture energy-based rescaling to eliminate mesh-dependent behavior. The model parameters are derived from unnotched tension tests in [0/90] and [+/−45] orientations. It is shown that the model is able to successfully predict the overall stress-strain response as well as the ultimate strength of all three notch configurations. In addition, the model predicts the notch size effect (notch-sensitivity) in a manner consistent with existing data on CMCs.