Thermomechanical Characterization of Glass Fiber- and Basalt Fiber-Reinforced Plastics

Abstract

The paper discusses measurement problems of heat deflection and glass transition temperatures of fiber-reinforced plastics by the Martens test and thermomechanical analysis (TMA). By using the Martens test, thermomechanical profiles were obtained for an epoxy binder and glass fiber- (GFRP) and basalt fiber-reinforced (BFRP) plastics under load ranging from 5 to 75 MPa. The onset temperature of severe deformation of GFRP and BFRP was found to be 15–20°С higher than that of the epoxy binder they were made of. GFRP and BFRP were tested by TMA in the lengthwise and crosswise fiber orientations. In crosswise measurement, TMA curves showed two noticeable inflection points corresponding to two thermal transitions. This can be explained by the cured binder being present in two states in the composites. The interfacial layer contiguous to the fibers had a lower glass transition temperature (Tg) than the matrix layer located in the interfibrous space; moreover, Tg of the composites under flexural load was similar to that of the matrix.