Development of an Interlaminar Toughness Test for Ceramic Matrix Composites

Interlaminar fracture properties in fiber-reinforced ceramic matrix composites have been found to be a limiting feature in certain applications, a limitation that intensifies at elevated temperatures. Few if any fibers bridge the cracks in the interlaminar direction, resulting in a weaker toughness and a higher probability of failure in this direction. The main challenge in evaluating interlaminar fracture toughness is the difficulty to detect the crack initiation and to measure the crack length directly at high temperature, primarily because of the limited visual accessibility of the area of interest. A DCB test-method using a ceramic wedge is developed. The method uses electrical resistance to monitor crack growth for melt-infiltrated woven SiC/SiC composites at room temperature, with the goal of doing the same at high temperature. In situ optical measurements of crack growth in addition to micro-CT post-inspection were used to validate and calibrate the resistance method. The estimated crack length was in excellent agreement with the measured crack length in the three considered specimen geometries. Preliminary estimates of Mode I energy release rate were also provided.