Effect of Notch-Induced Strain Gradients on the Applicability of Multiscale Approaches for Woven Composites

Abstract

Under load and structural features such as notches and fasteners act as stress concentrators and failure nucleation points, which can significantly reduce the strength and durability of the material. The focus of this work is on evaluating a computationally efficient multiscale approach for modeling woven composites in the presence of a strain gradient. The multiscale modelling approach is utilized to evaluate fiber or matrix failure. Then a series of homogenization steps are used to compute the effect of constituent failure on redistribution of strain at the structural level. The key feature of both the localization and homogenization steps is the representative volume element (RVE). But the critical assumption of an RVE is an average homogeneous state of strain across the RVE. Traditional multiscale methods that rely on an RVE are not readily extensible to models in which average strains vary appreciably across the RVE, such as can occur with woven composites in the presence of notches. In this study, we quantify the strain gradient present in open hole tension (OHT) specimens comprised of woven composites and assess the impact of these gradients on the RVEbased modeling approach. This is accomplished by conducting progressive failure simulations of a unit cell in the presence of a strain gradient and comparing with progressive failure simulations of the same unit cell under the same average homogeneous strain field. We find that the critical strain gradient is much smaller than anticipated and requires additional mesoscale studies to determine.