Interlaminar fracture and low-velocity impact of carbon/epoxy composite materials

The interlaminar fracture and the low-velocity impact behavior of carbon/ep oxy composite materials have been studied using width-tapered double cantil ever beam (WTDCB), end-notched flexure (ENF), and Boeing impact specimens. The objectives of this research are to determine the essential parameters g overning interlaminar-fracture and damage of realistic laminated composites and to characterize a correlation between the critical strain energy relea se rates measured by interlaminar fracture and by low-velocity impact tests . The geometry and the lay-tip sequence of specimens are designed to probe various conditions such as the skewness parameter, beam volume, and test fi xture. The effect of interfacial ply orientations and crack propagation dir ections on interlaminar fracture toughness and the effect of ply orientatio ns and thickness on impact behavior ar-e examined. The critical strain ener gy release rare was calculated from the respective tests: in the interlamin ar fracture test the compliance method and linear beam theory are used; the residual energy calculated from the impact test and the total delamination area estimated by ultrasonic inspection are used ill the low-velocity, imp act test. Results show that the critical strain energy release rate is affe cted mainly by ply orientations. The critical strain energy release rate me asured by the low-velocity impact test lies between the mode I and mode II critical strain energy release rates obtained by the interlaminar fracture test.