Strength and failure mode of CFRPs measured by short beam method of three point bending at high temparature

The strength by a short beam method of three point bending was measured for some CFRPs with varying fiber and matrix resin combination and their failure states were examined. The strength of every CFRP decreased linearly with increasing temperature. The strength retention at 200°C depended on the glass transition temperature of matrix resin. The retention for PMR-15 matrix resin was the highest, followed by MY720 resin and then EPIKOTE 828 resin. The failure mode of CFRP with EPI-KOTE 828 matrix resin tested at a cross head speed of 5mm/min was a mixture of shear and compression failure below 150°C, but pure shear failure at 200°C. Pure shear failure was also observed at cross head speeds less than 0.5mm/min, while compression failure in addition to shear failure was observed at cross head speeds more than 5.0mm/min. In CFRP with MY720 matrix resin, only shear failure was observed in the range of testing temperatures. In CFRP with PMR-15 matrix resin, buckling failure in addition to shear failure was observed up to 250°C. These differences in failure modes of different CFRPs were related with the ultimate strain of the matrix resin.