IN-SITU MONITORING OF FAILURE MECHANISMS IN BRITTLE MATRIX COMPOSITES USING ACOUSTIC EMISSION AND X-RAY FILM RADIOGRAPHIC TECHNIQUES

Abstract Two complementary nondestructive evaluation techniques were used to monitor the fracture processes in unidirectionally fiber-reinforced SCS-6 SiC/Si3N4 ceramic and Nicalon SiC/CAS glass-ceramic matrix composites subjected to tensile loading. The first technique employed a computerized acoustic emission system with resonant sensors. The primary fracture modes were recognized via three AE parameters for each signal analyzed: energy, peak amplitude, and event duration. These parameters were plotted against the analog signals for load and strain from a loadframe. A linear source location method was also utilized to locate the failure events within gauge section. The second technique used an X-ray film radiographic system mounted to the loadframe. A microfocus radiographic system was used before and after testing as well. Radiographic evaluations provided data on transverse crack formation, location of fiber breakage, and periodic matrix crack spacing for estimating interfacial shear strength. Cross-correlation between acoustic emission and radiographic results provided the necessary discrimi-nating power for tracking the failure sequence throughout the loading history.