Micromechanical Modeling of Time-Dependent Transverse Failure in Composite Systems

The time-dependent failure behaviour of transversely loadedcomposites is investigated, assuming that fracture is matrix dominated.Since the stress and strain state of the matrix in composite structuresis complex, the yield and fracture behaviour of a neat epoxy system isinvestigated under various multi-axial loading conditions. A gooddescription of the multi-axial yielding behaviour of the matrix materialis obtained with the three-dimensional pressure modified Eyringequation. The parameters of this three-dimensional yield expression areimplemented into a constitutive model, which has been shown to correctly describe the deformation behaviour of polymers under complex loadings.By means of a micromechanical approach, the matrix dominated transversestrength of a unidirectional composite material was investigated.Numerical simulations show that a failure criterion based on maximumstrain provides a good description for the rate-dependent transversestrength of unidirectional glass/epoxy composites. Furthermore, such astrain criterion is also able to describe the durability (creep) oftransversely loaded unidirectional composites.