Characterisation of unidirectional Carbon-Epoxy IM7-8552 in longitudinal compression under high strain rates

Abstract
A self-aligning Dynamic Compression Fixture, which can be used with a conventional Split-Hopkinson Pressure Bar, was developed to characterise the advanced composite carbon/epoxy material system IM7-8552 in longitudinal compression under high strain rates. The development of the dynamic experiment was supported by Finite Element Analysis, using a simple axi-symmetric elastic model of the dynamic test setup. Due to the quasi-brittle material behaviour in the longitudinal direction, a triangular shaped pulse is used, which creates a near constant strain rate while also ensuring dynamic equilibrium throughout the test. Tungsten-carbide inserts were used at the bar-specimen interfaces to prevent indentation of the bar ends due to the high strength specimen used. The results from the Split-Hopkinson Pressure Bar experiment, at a strain rate of approx. 100 s⁻¹, were compared with results from quasi-static tests using the same test setup. Analysing the first test results it is likely that the longitudinal compressive chord modulus of elasticity is not strain rate sensitive while an increase was found for the longitudinal compressive strength.