Finite-Element Micromechanical Strength Modeling and Parametric Investigation of Three-Dimensional Orthogonal Composites

Report No. ARL-TR-4355
Authors: Ryan L. Karkkainen; Jerome T. Tzeng
Date/Pages: January 2008; 34 pages
Abstract: Three-dimensional (3-D) reinforcement is often employed in thick composite parts to increase delamination resistance and through-thickness properties. Such materials are of particular interest for employment as insulators for the composite electromagnetic railgun insulator, which exhibits delamination as its primary failure mode. In the current study, a 3-D orthogonal woven S2-glass composite is investigated using finite-element micromechanics to characterize and evaluate its potential use in this target application. The representative volume element (RVE) of the 3-D woven microstructure is modeled directly through the 3-D finite-element model. Direct modeling of the exact microstructure allows for precise knowledge of the mechanics and failure modes of the microstructure under various loading conditions. Stiffness and strength are determined using a series of simulated characterization tests upon the RVE, with a detailed analysis of the resulting microstress field. Modeling results are verified by comparing experimental data. Tensile tests and Iosipescu shear tests have been performed to determine in-plane and transverse shear properties. Off-axis tensile tests were performed for further model validation. In-plane stiffness and strength were predicted with 90% or better accuracy. Transverse shear properties were less well predicted, but strength was still predicted within 86% accuracy. The micromechanical methods were then employed towards a parametric study of the effect of stitch density on promising improvement of delamination resistance and shear properties, as well as consequent loss of in-plane properties.
Distribution: Approved for public release
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Last Update / Reviewed: January 1, 2008