Monotonic and Fatigue Loading Behavior of an Oxide/Oxide Ceramic Matrix Composite

摘要

This thesis evaluates an oxide/oxide ceramic matrix composite, N720/ A, for high temperature aerospace applications. The composite consists of a porous alumina matrix reinforced by ten plies of Nextel 720 fibers in a balanced 8 harness satin weave. Monotonic tensile and fatigue tests were performed at room temperature and 1200 C. The effect of moisture on 1200 C fatigue life was also examined. Modulus, maximum and minimum strain, and stress-strain hysteresis were monitored to characterized fatigue damage. Retained strength of all specimens that survived 100000 fatigue cycles was tested. Microscopy and fractography were used to examine damage and fracture surfaces. N720/A was found to have good room temperature properties. At room temperature the ultimate tensile strength was 144 MPa and fatigue strength was 102 MPa. Fatigue damage involved mainly matrix cracking with no fiber-matrix debonding. At 1200 C the ultimate strength was 140 MPa and fatigue strength was 122 MPa. Fatigue damage was similar to room temperature with the addition of creep in the fibers. Exposure to moisture did not degrade fatigue performance. N720/A appears to be an excellent candidate for 1200 C applications with exposure to moisture.