Ultrasonic Characterization of Surface and Sub-Surface Defects in Ceramic Materials

The ultrasonic testing of ceramic materials is a two headed problem. First, the defect must be detected and second it must be characterized. Interior defects as small as 5 pm can be catastrophic as can surface cracks of less than a micrometer opening. There are a number of problems to be overcome in the detection of defects ultrasonically such as the amplitude of the ultrasonic signals and the maximum useful frequency of the ultrasound. These problems are being addressed by the development of high power, 100 to 200 MHz transducers and the improvement of electronics technology. This paper is concerned with the second problem, ie the characterization of defects and is divided into two parts, one concerned with interior defects and the second with surface defects. The common thread is the spectral analysis of the signals received from the defects