Kaiser effects in acoustic emission from composites during thermal cyclic-loading

Kaiser effects in acoustic emission (AE) behavior of composite laminates under repetitive thermal cyclic-loads are quantitatively analyzed to identify AE source mechanisms. The repetitive thermal loads brought about a large reduction, i.e. an exponential decrease, in AE total ring-down counts and AE amplitudes. It was thought that generation of most thermo-AE events during the first thermal cycle was not caused by crack propagation, but by secondary micro-fracturing due to abrasive contact between crack surfaces. For subsequent thermal cycles, on the other hand, a small number of weak thermo-AE events were generated due to frictional sliding contact. Such behavior of thermo-AE showed different characteristics according to specimen types and the maximum temperature in the thermal load cycles.