Applicability of two-step homogenization to high-crimp woven composites

Abstract

This paper examines applicability of a two-step homogenization approach to carbon/epoxy 3D woven composites. The first step of this approach involves microscale homogenization of the reinforcement consisting of wavy bundles of fibers. Finite Element Analysis (FEA) is used to obtain homogenized properties of explicitly modeled and homogenized wavy tows with fiber volume fraction of 70%. Two geometric parameters are investigated: crimp ratio and wavelength normalized by fiber diameter. Effective elastic properties are shown to be sensitive to the normalized wavelength parameter up to the value 50 at which point they reach asymptotic values and the separation of scales can be claimed.The resulting homogenized properties of the wavy tows are used to calculate the effective elastic properties of one high-crimp and two low-crimp 3D woven composites using FEA. The results of the numerical two-step homogenization are compared with experimental data and a simple Voigt model. Good correlation is observed between experimental results and the homogenization based on direct FEA. The considered Voigt approximation may be used as a reasonable first order estimate for Young’s moduli in low-crimp woven composites.