High-frequency acoustic emission induced by indentation fracture in brittle materials

Acoustic emission analysis is a method routinely applied in a variety of scientific, technological, and industrial fields. So far most of these applications have in common a limitation to sub-MHz frequencies. Recently, the frequency range available for acoustic emission analysis has been extended up to about 100 MHz. The present paper is a continuation of these investigations. Vickers hardness indendation in brittle materials has been used as a source of fracture and fracture-induced acoustic emission. The experimental setup consisting of a hardness tester, a focusing broadband transducer, and a digitizing signal analyzer is designed for frequencies up to about 400 MHz. It can be realized or even improved in a number of laboratories with standard experimental instrumentation. The highest acoustic emission frequency detected in the present paper is about 150 MHz. This frequency limit is set by the transducers used. The method has been applied in order to investigate the presence and characteristics of acoustic emission in slide glass, a single crystal of Si, and a fine-grained AIN ceramic. Received acoustic emission signals have been analyzed with respect to the temporal shape. the amplitude spectrum, and the stage of occurrence relative to the indendation loading/unloading cycle.