Rate effects on the delamination fracture of multidirectional carbon-fiber/epoxy composites under mode I loading

The present study has shown the experimental results for characterization of the mode I delamination fracture of continuous carbon fiber/epoxy multidirectional composites under a wide range of test rates, up to high rates of 11.4 m/s. At the slow rates of test less than or equal to1.0 x 10(-1) m/s the delamination fracture energy showed a rising R-curve, a strong function of the length of propagating crack due to the large extent of crack jumping and following fiber bridging. At the high rates of test greater than or equal to1.0 m/s any loads recorded by the load cell were largely obscured by such dynamic effects as spring-mass oscillations and flexural wave reflections. In this respect, Equation 11, requiring the values of the actual arm displacement and flexural (axial) modulus, was better for the deduction of G(I)C. However the maximum value of G(I)C so obtained was considerably underestimated. By increasing the rate up to 1.0 x 10(-1) m/s, there were little differences in the delamination fracture behaviors, whereas at high rates >1.0 m/s the maximum values of G(IC) decreased considerably. In the case of a short initial crack length, however, the maximum values largely increased at a rate of 11.4 m/s. (C) 2001 Kluwer Academic Publishers.