Digital correlation system for nondestructive testing of thermally stressed ceramics

We report on the development of an automated digital speckle system for use in the nondestructive testing of thermally stressed ceramics. The system is based on a laser-speckle technique known as speckle-pattern correlation and uses a CCD camera and a microcomputer to allow real-time testing of the ceramic samples. This arrangement makes use of decorrelation in the laser speckle image structure, which results from microstructural changes in the surface topology, to probe for surface defects on the thermally stressed materials. Acorrelation tracking procedure was used to allow corrections to be made to the correlation signal arising from bulk motion of the sample. Results are presented that demonstrate the capability of the correlator for distinguishing between ceramic components on the basis of their response to thermal loading.