FLEXURAL FAILURE MECHANISMS IN UNIDIRECTIONAL GLASS-FIBER-REINFORCED THERMOPLASTICS

The effect of the matrix modulus on the failure mechanisms in flexure of unidirectional glass fibre-reinforced composites with soft thermopl astic Hytrel matrices has been studied. Failure always originates on t he compression side of the specimen. An increase in the matrix Young's modulus leads to a change in the failure mode from cooperative fibre microbuckling to delamination splitting microbuckling. The bending str ength increases significantly with increasing matrix modulus. Cooperat ive fibre microbuckling is a catastrophic phenomenon without significa nt damage occurring in the composite system prior to the abrupt failur e. Fibres are buckled both in the plane and normal to the plane of the compression surface, and the bending strength is controlled by the sh ear modulus of the composite. Delamination splitting microbuckling is associated with matrix splitting and consists of a relatively gradual accumulation of localized surface delaminations followed by buckling o f fibre bundles. In this mechanism, the bending strength is dominated by the composite shear strength and the fibre/matrix adhesion.