Crack-growth resistance behavior of mode-I delamination in ceramic matrix composites

Mode-I delamination crack growth in Ceramic Matrix Composite (CMC) materials is studied using experiments and associated numerical modeling. Double cantilever beam tests were conducted to measure delamination growth characteristics and the associated mode-I critical energy release rate. The tests revealed significant crack growth resistance (R-curve) behavior with the load carrying capacity increasing with the delamination growth. The experimentally observed load-displacement response could not be explained by linear elastic fracture mechanics or by a two-parameter triangular cohesive finite element models. The observed crack growth resistance behavior is explained by incorporating cohesive traction-separation relationship with a bilinear softening resulting in a long "tail", which is interpreted and modeled as a superposition of two traction-separation relationships representing mechanisms associated with near crack-tip region and fiber-bridging in the crack-wake, respectively. (C) 2017 United Technologies Corporation. Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.