Optical strain fields in shear and tensile testing of textile reinforcements

This paper presents deformability tests oil textile reinforcements in biaxial tension and shear using digital image correlation to calculate strain fields from in-plane images. Macro-scale strain fields (i.e. strain gauge length >= Repetitive Unit Cell) are applied to assess the reliability of loading conditions in tensile and shear tests, and to verify the assumption that the tensile state affects the shear resistance of a weave. Picture frame shear tests on a glass weave, a glass-PP weave and a carbon NCF are presented. The glass-PP weave is also tested in biaxial tension and in shear at three different tensile preloads. It is concluded that full-field optical techniques are essential to reliably assess the textile deformation and homogeneity of loading in textile testing. Significant tensile-shear interaction is observed. Nevertheless, further verification is recommended to assess the influence of uncontrolled yarn tensile load and the frame/fabric shear discrepancy on the empirical shear resistance. (c) 2007 Elsevier Ltd. All rights reserved.