The mechanisms of damage initiation and growth of random short fiber SMC specimens with a notch during quasi-static loading and the relationship between the damage zone size and the acoustic emission (AE) have been studied. The results obtained are shown as follows: (1) The damage in the notched SMC specimen initiates in the matrix at the tip of notch and it propagates to the fiber dominant area with an increase of load. The damage in the matrix dominant area is observed in a form of crack at

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... e interfaces between resin and particles of calcium carbonate. It is found that the damage in the fiber dominant area is initiated by debonding at the interfaces between fiber and matrix or in fiber strand. (2) The damage zone at a notch tip can be divided into the main-damage and the sub-damage zones. The AE cumulative event counts and the AE total energy correspond to the growth of damage zone. Therefore, it can be concluded that the damage changes from the stable growth to the unstable one according to the AE cumulative event counts or the AE total energy when the sub-damage zone approaches to the critical value. (3) It is clarified that the growth of sub-damage zone is represented by the stress intensity factor KI considering the effect of main-damage zone.