Holographic evaluation of ceramic materials

The coherent optical technique of holographic correlation is applied to the nondestructive evaluation of ceramic materials. A Fresnel correlator is used to holographically construct a matched filter to a small test area on the surface of a silicon nitride ceramic. The subsequent change in correlation signal intensity, from localized microstructural changes occurring on the ceramic surface, is determined as the sample is subjected to thermal stress. A novel method to detect and quantify any loss in correlation signal strength arising from the bulk movement of the ceramic sample within its support is described. Results are presented which show that the correlation technique is capable of evaluating the characteristics of ceramic materials in terms of their response to thermal stress.