Non-contact measurement of acoustic emission in thin specimen by laser interferometer

Acoustic emission (AE) is very useful technique to understand the micro fracture behavior in materials. However, it is difficult to monitor AE behavior in small or thin specimen compared with the size of transducer. Recently we developed the non-contact AE measurement system using laser interferometer for various applications, and it was successfully used to detect AE signals of ceramic coating materials during thermal cycle tests. Dielectric strength is a key property for dielectric ceramics such as barium titanate and titania, and it is very important to evaluate dielectric failure in these materials. However, conventional piezoelectric transducer could not be applied to this test. It is difficult to attach a transducer to specimen because thickness of specimen is thin compared with that of mechanical test, and conductivity through transducer is not desired for dielectric breakdown test. We successfully detected AE signals during dielectric breakdown test using laser interferometer. AE sources such as dielectric breakdown and partial discharge were also clearly identified by frequency and location analysis of AE waveforms.