Simulation of manufacturing induced fiber clustering and matrix voids and their effect on transverse crack formation in unidirectional composites

Abstract

This work is a contribution to the fields of computational micromechanics and virtual testing of fiber reinforced composite materials. Particular focus is on deriving trends related to the early failure events leading to crack formation in unidirectional composites under transverse tension. A simulation scheme is proposed to capture fiber clustering and matrix microvoids in a resin infusion process. A systematic procedure is developed to quantify these manufacturing induced defects in terms of fiber displacements (mobility) from an initially dry fiber bundle to the fully resin-infused composite. Using established methods for stochastic characterization of microstructures, the minimum size of a representative volume element (RVE) is estimated and its multiple realizations are used in an embedded cell model for finite element based computation of the local stress fields. Strain energy based point-failure criteria are then employed to ascertain occurrence of the most likely first failure mechanism. A matrix crack is assumed to form by coalescence of the point-failures as precursors. Parametric studies are performed to clarify the effects of the degree of fiber clustering, the volume fraction of matrix microvoids and the constituent properties on transverse crack formation. Experimental data available in the literature support the predictions of the simulations.