Effect of fiber waviness on the high-strain-rate behavior of composites

The effect of fiber waviness on the high-strain-rate behavior of carbon/epoxy composite materials was investigated. Falling weight impact and Split Hopkinson Pressure Bar systems were developed for basic characterization of unidirectional aligned composites in compression at strain rates up to 1800 s^-1. Seventy-two and forth-eight-ply unidirectional carbon/epoxy (IM6G/3501-6) laminates loaded in the longitudinal and transverse directions were characterized. Compression tests on 45° off-axis laminates of the same unidirectional material were also conducted to obtain the in-plane shear stress-strain behavior. Strain rates over a wide range, from quasi-static up to 1800 s^-1, were recorded. An incremental analysis was then used to predict the high-strain-rate behavior of composites with fiber waviness using the results obtained from the strain rate characterization. It is shown that, under longitudinal compressive loading, the nonlinear stress-strain behavior shows significant stiffening as the strain rate increases due to the shear component involved.