Damage Evolution and Characterization of SiC/SiC Ceramic Matrix Composites Using Micro-Computed Tomography Techniques

Abstract

In situ x-ray computed tomography was performed on melt infiltrated (MI) SiC/SiC ceramic matrix composites under tension in order to observe and quantify damage progression. The advanced light source (ALS) at Lawrence Berkeley National Lab was utilized to test two types of composite architectures, unidirectional and cross-ply, where each specimen was imaged at increasing tensile stress increments. Damage such as matrix cracking and fiber fragmentations were detected and measured for each specimen at each imaged stress increment. From the x-ray tomography observations, three different types of matrix cracks were observed including partial cracking, bifurcating cracks, and joining cracks. The onset of matrix cracking that was observed using in situ x-ray computed tomography was compared to mechanical model predictions. The comparison between the experimental observations and the mechanical models were similar, within the range of 100 MPa. The final matrix crack spacing was also compared to predicted debond lengths and shear lag distances. Fiber fragmentations were observed within the volume of each specimen and the breaks were quantified. The number of fiber fragmentations within a composite specimen continued to increase until the specimen broke. The opening height of each fiber fragmentation was qualitatively examined and two main observations were determined. First, as applied stress continued to increase, the initial fiber fragmentation opening also continued to increase. Second, fiber fragmentations that occurred at higher applied stresses have larger fiber fragmentation openings than ones that occurred at lower stresses. Using x-ray computed tomography allowed for the study of the relationship between fiber damage and the microstructure in terms of fiber locations and fiber clustering.