The effect of strain rate on the orientation of the fracture plane in a unidirectional polymer matrix composite under transverse compression loading

Transverse compression tests on a unidirectional composite were performed under quasi-static and high-rate loading conditions using servo-hydraulic machines as well as a direct impact Hopkinson bar. Aside the expected increase of compressive strength with increasing loading rate, a change of fracture plane orientation was observed. For quasi-static loading conditions, the fracture angle was 54.5 degrees, for high rate-loading conditions this increased to 65 degrees. Assuming a Mohr-Coulomb type of fracture for unidirectional composites under transverse compression loading, the change of fracture plane orientation indicates a rate dependency of the internal friction angle phi, which has not previously been reported for composite materials.