The fatigue fracture mechanism of class A-SMC which has been developed for the outer panel in automobiles was studied by determining the parameters of acoustic emission (AE) detected during its fatigue fracture process. The results obtained are as follows:
(1) The macroscopic fatigue fracture behavior is accurately reflected by the AE event count rate and the total AE energy, which are the most proper AE parameters to represent the macroscopic fracture pattern of composite materials.
(2) It is confirmed that the fatigue fracture mechanism can not be explained by the AE amplitude, even if by using the results of the macroscopic and microscopic observations of fatigue fracture surface.
(3) The microscopic fracture mechanism during the fatigue test can be clarified by observing the fracture surface microscopically and applying the relation among the AE frequency, the load and the power spectrum obtained on the static tensile test to the relation among the AE frequency, the number of cycle and the power spectrum obtained in the tensile fatigue test. It is found that the most proper AE parameter to represent the fatigue fracture behavior of constituent elements in the composite materials is the AE frequency spectrum.