EVALUATION OF INTERFACIAL PROPERTIES IN GLASS-FIBER EPOXY-RESIN COMPOSITES - RECONSIDERATION OF AN EMBEDDED SINGLE FILAMENT SHEAR-STRENGTH TEST

An embedded single-filament shear-strength test was employed to explore the effect of the reinforced interface on the fracture of single filaments in glass fibre-epoxy resin composites. The interfacial effect was evaluated not only by critical fibre length but also by the fracture process of an embedded single filament observed by applying tensile load to the composites. The mean fragment length, measured at different tensile stresses, decreased with an increase in stress and finally reached a value correlated with critical fragment length. Interfacial reinforcement by silane treatment affects the fracture process rather than the critical fibre length. The behaviour was examined in several factors, such as filament diameter, the tension of filament on the moulding of composites, and the scatter of the composites in mechanical properties. A useful method was proposed to exclude such scatter: specimens treated on a half-length of embedded filament were subjected to this test. The present method leads us to confirm that the reinforced interface has no effect on the critical fibre length, while it does promote the progress of the fracture.