Characterization of intralaminar strengths of virtually cured polymer matrix composites

The effect of the curing process on the mechanical response of fiber reinforced polymer matrix composites, IM7/Epoxy 862, is studied using a novel computational model. Virtual testing is performed using the Finite Element Method (FEM) at the microscale where Repeating Unit Cells (RUCs) are analyzed to determine strengths and elastic properties of a thin lamina. Two sets of Boundary Conditions (BCs) during curing are studied; Periodic (PBCs) and Flat (FBCs). The commercial codes, ABAQUS/Standard and ABAQUS/Explicit have been used as the FEM solver, supplemented by user written subroutines, that model the curing process and the mechanical response including the onset of damage and subsequent failure. The transition from a continuum to damage/failure state is effected by using the Bazant-Oh Crack Band model, which preserves mesh objectivity. Results are presented for a randomly packed RUC which is first subjected to curing and subsequently to mechanical loading. It is assumed that damage can initiate during the cure cycle if the internal stresses exceed prescribed values and that this damage can grow in the form of cohesive cracks. After the curing of the RUCs, virtual mechanical loading programs are studied. In this latter stage, the cured RUCs, which may contain internal damage and residual stresses are further subjected to additional stresses induced by the mechanical loading. The results clearly show the influence of the curing cycle (the effects of manufacturing) on the mechanical response.