DIGITAL CORRELATION SYSTEM FOR NONDESTRUCTIVE TESTING OF THERMALLY STRESSED CERAMICS

We report on the development of an automated digital speckle system fo r use in the nondestructive testing of thermally stressed ceramics. Th e system is based on a laser-speckle technique known as speckle-patter n correlation and uses a CCD camera and a microcomputer to allow real- time testing of the ceramic samples. This arrangement makes use of dec orrelation in the laser speckle image structure, which results from mi crostructural changes in the surface topology, to probe for surface de fects on the thermally stressed materials. A correlation tracking proc edure was used to allow corrections to be made to the correlation sign al arising from bulk motion of the sample. Results are presented that demonstrate the capability of the correlator for distinguishing betwee n ceramic components on the basis of their response to thermal loading .