Numerical analysis of resin-rich areas and their effects on failure initiation of composites

Resin-rich areas in composite laminates can occur as inter-laminar resin 'layers' between plies or as intra-laminar resin 'pockets' within a single layer. In this work, numerical methods are used to study the effects of resin pockets on the transverse stiffness and failure initiation of carbon-epoxy composites. Random, or non-uniform, representative volume elements (RVE) with and without embedded resin pockets were studied. Three different types of samples with predefined volume fractions (V-f) were analyzed, and data relating to the influence of resin pockets on homogenized stiffness and the strain at which failure initiates was collected and reported. Based on a control sample for each volume fraction, two methods were used to create RVE samples with resin pockets. In one, the distances between fibers were maintained and fibers removed to create the resin pocket, with a corresponding decrease in (V-f). In the second method, the V-f was maintained and fibers were moved to create the resin pocket, with a corresponding reduction in the distance between fibers. It is shown that intra-laminar resin pockets can reduce both the stiffness and the failure strain of composite materials. Stiffness was reduced in samples where the resin pocket resulted in a reduced volume fraction. For samples with the same volume fraction, particularly for high V-f composites (e.g. 60%), the failure initiation strain in the matrix was, on average, 20% lower for samples with resin pockets compared to samples without resin pockets.