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

Abstract

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 ≤1.0 × 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 ≥1.0 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 _IC. However the maximum value of G _IC so obtained was considerably underestimated. By increasing the rate up to 1.0 × 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.