ANALYSIS OF FRACTURE MECHANISMS IN SHORT FIBRE COMPOSITES IN RELATION TO FIBRE ORIENTATION

摘要

The relationship between fracture orientation, fracture mechanisms and fracture toughness in short fibre composite materials, was investigated using three different materials: a polyamide 6.6 and a polyoxymethylene containing 30wt% of glass fibre and a polyarylamide with 50wt% of glass fibre. Plates with uniform, unidirectional fibre orientation were prepared and single-edge notched three-point bending test specimens were cut at varying angles between the notch direction and the direction of the aligned fibres. The critical stress intensity factor K_C and fracture energy G_C measured at fracture initiation in quasistatic tests present linear relationships with fibre orientation with different slopes over different ranges of the orientation factor. This suggests a transition in fracture mechanisms: matrix fracture and fibre debonding are the prevailing fracture mechanisms at low values of the fibre orientation factor, while at high values the main fracture mechanisms are fibre breakage and pull-out. Fractured specimens were examined using a scanning electron microscope to assess the fracture mechanisms involved.