Non-contact damage monitoring by laser AE technique

AE method is a well-known technique for in-situ monitoring of fracture behavior by attaching piezoelectric transducer. However, conventional AE transducer cannot be used at elevated temperature or severe environment. Laser based ultrasonic (LBU) technique has been developed to characterize materials properties and detect flaws in materials. We developed the AE measurement system with laser interferometer to apply this technique to microfracture evaluation in various materials. AE during sintering of alumina ceramics and thermal spying of alumina powder on steel substrates were successfully measured by laser interferometers. The effect of processing parameters on AE behavior was clearly observed by analyzing AE waveforms. One of the most advantages of this laser AE technique is to estimate the temperature where microcracks are generated. These results could give a feed back to control processing conditions in order to avoid damage in materials. It was concluded that the laser AE method was very useful to detect microcracks in ceramics during fabrication.