In this study, quasi-static and impact three-point bending tests were conducted on specimens using carbon fibers with different fiber orientations and elastic modulus. Specimens with ±45°fiber orientation showed higher flexural strain rate sensitivity than those with 0°fiber orientation. This is due to the effect of the matrix epoxy resin on the flexural modulus. Furthermore, it was confirmed that the flexural modulus increased as the deflection rate increased for all three types of specimens with different fiber strengths. Especially, specimens using fibers with an elastic modulus of 235 GPa and those using fibers with an elastic modulus of 280 GPa exhibited almost the same flexural rate sensitivity in the range from quasi-static to impact flexural rate. This suggests that the matrix epoxy resin governs the deflection rate dependence of the flexural modulus.
Hajime et al. (Wed,) studied this question.