Relationships between acoustic emission signals and physical phenomena during indentation

A commercial piezoelectric acoustic emission transducer has been used in conjunction with nanoindentation techniques to study the relationship between acoustic emission signals and discrete physical events to identify the type and strength of an event. Indentations into tungsten and iron single crystals have been used to study dislocation generation and passive film failure. In addition, indentations made into a thin nitride film on sapphire have been used to cause film delaminations. Parameters such as signal rise time and frequency for a piezoelectric sensor are related to sample geometry, and not to the type of event which caused the acoustic emission signal. As a possible calibration for acoustic emission sensors, the most meaningful parameter is the acoustic emission energy, which has been shown to scale with the elastic energy released during the event. The measured values of elastic energy released correspond very closely to those calculated using Hertzian contact mechanics.