On-axis and off-axis compressive behavior of pultruded GFRP composites at elevated temperatures

In this study, the on-axis and off-axis compressive behavior of pultruded unidirectional glass fiber reinforced polymer (GFRP) coupons at elevated temperatures were investigated. The coupons with fiber orientations of 0 degrees, 30 degrees, 60 degrees and 90 degrees to the compressive loading axis were tested from 20 degrees C to 180 degrees C. The specimens under on-axis compression clearly exhibited a kinking failure mode at elevated temperatures, while the in-plain shear failure occurred in the specimens of 30 degrees and 60 degrees off-axis compression, and the out-of-plain shear failure occurred in 90 degrees off-axis specimens. The failure modes were hardly affected by the temperatures except that the GFRP skin wrinkling captured in off-axis compression specimens above 60 degrees C. As expected, the compressive strength and elastic modulus were significantly reduced with the increase in temperature. Moreover, the compressive strength of on-axis and off-axis specimens exhibited similar retention rate at each targeted temperature, while the elastic modulus of on-axis specimens showed a higher retention rate than those of off-axis specimens. The analytical studies showed that the degradation of modulus and strength of all specimens generally followed the inverse rule of mixture. In addition, the off-axis strength and elastic modulus were estimated by the Hankinson's formula.