Strain-rate effects on unidirectional carbon-fiber composites

Strain-rate effects on mode I fracture of unidirectional carbon-fiber tow composites corresponding to crack propagation parallel to the fiber tow direction was investigated. Precracked unidirectional stitched carbon-fiber specimens were subjected to a static and low-velocity-impact three-point bend test. The crack position as a function of time and hence the crack-propagation velocity were measured with the help of special crack-propagation gauges and a high-resolution digital camera. Load vs; load point displacement was measured for every test. The effect of strain rate on fracture energy was characterized. The Iosipescu shear test under static and low-velocity-impact loading conditions was used to characterize the rate-dependent shear response of the material. In addition, tension and compression responses were characterized using American Society for Testing and Materials standard test configurations. It is found that the mode I fracture energy decreases with an increase in the rate of loading.