Effect of the stress amplitude and environment temperature on the fatigue fracture mechanism of polycarbonate

The changes of the dynamic viscoelasticity during the fatigue process and t he fracture surface phases were investigated to explain the effects of the stress amplitude and environment temperature on the fatigue fracture mechan ism of polycarbonate (PC) in this study. The results are as follows: (1) PC is a typical ductile material because PC has a high heat transformation te mperature. (2) For the fatigue life change at each testing temperature. the fatigue life on the levels of low and high stress would decrease with the increase in the stress amplitude : however, the reverse phenomenon would ap pear on the level of the middle stress. But this trend would be slight. The increase in the fatigue lift is related to the partial ductile fracture du ring the crack propagation process and the rise in the molecule orientation due to the specimen extension. (3) The fatigue life would decrease with th e increase in testing temperature. The degree of decrease on the high stres s level was more than that on the low stress level. ( 1) The fatigue fractu re mechanism is concerned with the E' value in the fatigue process and the change of tan delta on each stress amplitude at each testing temperature. ( 5) The fatigue fracture mechanism at high temperature is similar to that at room temperature.