A novel combination of micromechanical testing and thermal analysis : to investigate the temperature dependence of interfacial adhesion in fibre reinforced polymer composites

The present work focuses on our investigation of the hypothesis that a significant fraction of the level of apparent interfacial shear strength (IFSS) in glass fibre-reinforced polymer composites can be attributed to a combination of thermal residual stress and static friction at the fibre-polymer interface. In order to obtain information on the temperature dependence of fibre-matrix IFSS, a TA Q400em Thermo-Mechanical Analyser (TMA) was adapted to enable interfacial microbond testing to be carried out in a well-controlled temperature environment. Room temperature test results obtained by TMA-microbond testing showed excellent comparability with those obtained by normal microbond testing. The temperature dependence of IFSS of glass fibre-polypropylene was measured in the range from -40 degrees C up to 100 degrees C. The IFSS showed a highly significant inverse dependence on testing temperature. The temperature dependence of the glass fibre-polypropylene IFSS could be fully accounted for by the variation of residual radial compressive stresses at the interface with the test temperature. The temperature dependence of IFSS of a glass fibre-system was measured in the range from 20 degrees C up to 150 degrees C. In this case it was found that the residual thermal stress did not appear to fully account for the temperature dependence of IFSS in this glass fibre-epoxy system. Nevertheless, the IFSS results also clearly showed a strong correlation with the sample temperature. It was noted that the most significant change in IFSS took place across the matrix glass transition temperature in both cases. Consequently the IFSS temperature dependence appears to correlate closely with the matrix storage modulus measured by Dynamic Mechanical Analysis in both polypropylene and epoxy composites