Acousto-ultrasonic evaluation of ceramic matrix composite materials

Acousto-ultrasonic nondestructive evaluation of ceramic composite specimens with a lithium-alumino-silicate glass matrix reinforced with unidirectional silicon carbide (NICALON) fibers was conducted to evaluate their reserve of strength. Ceramic composite specimens with different amount of damage were prepared by four-point cyclic fatigue loading of the specimens at 500 C for a different number of cycles. The reserve of strength of the specimens was measured as the maximum bending stress recorded during four-pointed bending test with the load monotonically increased until failure occurs. It was observed that the reserve of strength did not correlate with the number of fatigue cycles. However, it was also observed that higher values of the stress wave factor measurements correspond to higher values of the reserve of strength test data. Therefore, these results show that the acousto-ultrasonic approach has the potential of being used to monitor damage and to estimate the reserve of strength of ceramic composites