Dynamic punch shear characterization of twill weave graphite/epoxy composites

In this study, the high strain rate response of twill weave graphite/epoxy composites under punch shear mode was characterized. 24-layer laminates of twill weave graphite fabrics were fabricated using a relatively inexpensive vacuum assisted resin infusion moulding process (VARIM) with a low viscosity SC-15 resin system. Samples of nominal size 25 by 12.7 by 4 mm were cut from the laminates for high strain rate testing. High strain rate punch shear tests were carried out with a modified Split Hopkinson Pressure Bar setup. Samples were loaded in punch shear mode through the thickness. Varying the breech pressure allowed testing at different strain rates in the range of 1400/s to 3800/s. Samples were tested at room and three elevated temperatures of 52 degrees C, 79 degrees C and 107 degrees C. The samples exhibited increasing peak shear stress with increasing strain rate at all temperatures. However, the peak stress decreased with temperature for a given range of strain rates. Failure modes were characterized with scanning electron microscopy, which revealed the degradation of the fibre-matrix interface with increasing temperatures.