Static Fracture Behavior of a Ceramic Matrix Composite at Elevated Temperatures

This study investigated systematically the damage initiation damage progression, and failure modes of a ceramic matrix composite, Nicalon/CAS, when loaded in tension at elevated temperatures in the presence of air. A cross-ply lay-up, [0/90]2s, was studied. The primary means of analysis were stress-strain data taken during monotonic and incremental load tests and crack density assessments. Testing was conducted at room temperature 700°C, and 850°C. The stress-strain response was consistent for monotonic and incremental loading, except for a decrease in failure load at the elevated temperatures. Initial damage progression was also consistent, but the damage leading to failure and the final failure mode at 850°C were different due to the oxidation of the fibers. The oxidation created a brittle interface between the fiber and matrix, which resulted in an increase in fiber pull-out at the failure surface.