Fracture toughness test of short fibre composites

A detail study on the failure process of short glass fibre reinforced phenolic resin composite is presented. A fracture mechanics approach has been adopted and Mode I tests have been caried out. The effect of specimen orientation has been investigated. It has been shown that for samples with L-T orientation the fracture energy G_c weekly depends on the width to thickness ratio and samples thickness while for samples with T-L orientation the fracture energy depends on the geometrical parameters more pronouncedly. To follow the failure processes an acoustic emission technique including amplitude analysis of acoustic events has been applied. Three groups of acoustic events with different amplitude range have been distinguished. The observed changes in acoustic events amplitudes show that different mechanisms are involved in fracture processes. From acoustic emission studies it is shown, that critical failure event may preceded the fracture of sample.