Experimental Study of Mode-I Fracture Toughness of Heat-Resistant Composite

摘要

This work studied interlaminar fracture toughness of a unidirectional polyimide/carbon-fiber laminate over a wide range of temperature and crack speeds by double cantilever beam (DCB) test. The new electric-resistant method has been developed for crack-length measurement. By using this method, the mode-I fracture toughness of heat-resistant composite has been measured continuously and correctly in temperature chamber. This method has been compared with the strain-gage method and linear beam theory for verification. The effects of temperature and loading rate on the interlaminar fracture toughness of unidirectional heat-resistant composites have been studied. The following conclusions can be drawn from the results presented. Strain energy release rate, G_(IC) decreased with temperature increase. Strain energy release rate G_(IR) has been almost constant for loading speed and temperature. Fiber bridging occurred in the higher in temperature condition. If the number of fiber bridging in the crack region has been large, closure force might be big. And this led to the conclusion that bridging fibers play important roles in the load-displacement curves and crack propagation behavior.