No abstract

No abstract

Ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced composites have received widespread attention in the literature due to their attractive ballistic protection attributes. Recently, investigators are recognizing and demonstrating the significant role that interlaminar shear has on their ballistic performance. In this paper, we present a characterization methodology to quantify the quasi-static interlaminar shear strength and nonlinear interlaminar shear stress-strain response of UHMWPE composite laminates. The methodology uses a tension loaded double-lap coupon design to introduce interlaminar shear loading. Coupon displacement measurements using Digital Image Correlation (DIC) coupled with Finite Element Analysis (FEA) incorporating nonlinear material behavior and traction-separation behavior is an integral part of the data reduction scheme. This research provides a unique methodology for developing interlaminar shear constitutive models for UHMWPE composite laminates, which are critically needed to improve the accuracy of ballistic impact simulations for the development of more efficient armor designs.

As a part of the Second World-Wide Failure Exercise, a three-dimensional nonlinear maximum progressive strain model, based on laminate analysis, is employed to make blind predictions for 12 test cases representing failure envelopes and stress strain curves for isotropic, unidirectional, and multidirectional composite laminates. This approach allows for redistribution of ply stresses and differentiation of the various potential modes of failure. These cases include initial and final ply failure envelopes under tri-axial loading, as well as 3 cases, requiring nonlinear stress-strain analysis. Comparison of predictions with actual experimental data will be made in Part B of the Second World-Wide Failure Exercise.

This article represents our contribution to Part B of the 2nd Worldwide Failure Exercise (WWFE-II), where comparisons between epoxy/lamina/laminate response and failure predictions, based on maximum strain failure criterion, and experimental results are made. Correlations between actual test data and our nonlinear stress-strain response and failure envelope predictions under multi-axial loading for 12 different case studies are presented and discussed. Although our approach to modeling composite failure ranked high when applied to biaxial in-plane loading analysis, the theory does not consistently capture the inherent strengthening mechanisms that can be attributed to triaxial loading and hydrostatic pressure. It is expected that the incorporation of a strain-based ply-level failure criterion that introduces some form of strengthening mechanism under a three-dimensional stress state would significantly improve the accuracy of our predictions.