Flexural failure mechanisms in unidirectional glass fibre-reinforced thermoplastics

Abstract

The effect of the matrix modulus on the failure mechanisms in flexure of unidirectional glass fibre-reinforced composites with soft thermoplastic Hytrel matrices has been studied. Failure always originates on the 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 strength increases significantly with increasing matrix modulus. Cooperative fibre microbuckling is a catastrophic phenomenon without significant damage occurring in the composite system prior to the abrupt failure. Fibres are buckled both in the plane and normal to the plane of the compression surface, and the bending strength is controlled by the shear 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 of fibre bundles. In this mechanism, the bending strength is dominated by the composite shear strength and the fibre/matrix adhesion.