Fracture toughness studies of fibre reinforced plastic laminates

Abstract

The mode of fracture and the origins of fracture work have been investigated for several fibreglass laminate constructions. Crack propagation in woven fabric and cross-plied unidirectional ply laminates with fibres parallel and perpendicular to the load direction was resisted by splitting between the fibres in the load direction at the crack tip. Crack propagation occurred by successive split formation and failure of the region of fibres adjacent to the split. Although crack tip damage was often extensive, fracture was governed by the classical crack tip stress singularity in all cases. The fracture work determined from notched tension tests was quantitatively associated with the elastic strain energy decrease in the region of fibres adjacent to the split at the crack tip when the crack advanced. Variations of up to a factor of fifteen in longitudinal ply fracture work were realized by varying the ply configuration of Scotchply laminates. Predictable increases in fracture work with fibre volume fraction and woven fabric ply orientation were also achieved.