Energy absorbing mechanisms in short-glass-fibre-reinforced polypropylene

The tensile load elongation curves to failure of samples cut along different directions from a extruded sheet of short-glass-fibre-reinforced polypropylene having good fibre alignment along the extrusion direction, were obtained at a strain rate of 0·01 min^?1. The work of rupture was calculated from the area under the stress extension curves. The contribution made by some of the energy absorbing mechanisms like plastic deformation of the matrix, debonding, and fibre pull-out to the total work have been considered in some detail. In the extrusion direction, and at angles up to 30° to this direction, the interfacial shear stress and load transfer are high. Consequently, the plastic deformation of the matrix througout the specimen volume, and particularly around fibre ends, makes a dominant contribution to the work of rupture, with a small but significant contribution from debonding and also from fibre pullout at the fracture surfaces. At larger angles, the interfacial shear stress and load transfer are relatively lower, and the work of rupture is considerably less. Supporting evidence for these observations from acoustic emission studies and electron micrographs of raptured surfaces is also presented.