EXPERIMENTAL CHARACTERIZATION OF THE IN-PLANE SHEAR RESPONSE OF WOVEN POLYMER MATRIX COMPOSITES UNDER INTERMEDIATE STRAIN RATES

Abstract

The need for advanced material models to simulate the process of deformation, damage and failure of polymer matrix composites (PMCs) under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. Experimental stress vs. strain curves are needed at different strain rates for progressive damage modeling of dynamic failure. Matrix-dominated deformation modes are particularly challenging as they exhibit nonlinear behavior and rate dependence. In particular, in-plane shear is known to exhibit significant nonlinear response due its matrix dominant deformation leading up to failure. The purpose of this work is to experimentally characterize the in-plane shear deformation response of woven carbon/epoxy fabrics under intermediate strain rates (10-1 to 100 s-1). For this work, plain weave carbon fabrics with 3k and 12k tows are manufactured by VARTM. Testing is done using a servo-hydraulic load frame and 2D digital image correlation (DIC) is used to obtain experimental stress vs. strain curves following ASTM D7078M. Comparison between quasi-static (10-3 s-1) and intermediate experimental stress strain curves show an increase in ultimate strength and no significant change in modulus with increased loading rate. Investigations into the development of areas of localized high strain are observed which are attributed to the growth of meso-scale fiber tows damage. Surface level measurements from DIC and qualitative observations from high speed camera imaging reveal that cracks initiate and develop in the matrix gap between tows and at fiber undulation regions of the plain weave. These then develop into bulk cracks that grow parallel to the load. Higher loading rates have shown increased strength under in-plane. In conclusion, 2D DIC and the v-notched shear test method was able to characterize rate effects under intermediate shear loading of woven polymer matrix composites deformation response. High resolution DIC reveals localized mesoscale strain inhomogeneity that plays a key role in the initiation and evolution of bulk fracture in woven composite architecture which was captured for well for the 12k tow material.