COMPUTER-AIDED PHOTOELASTIC ANALYSIS OF ORTHOGONAL 3D TEXTILE COMPOSITES .1. WHOLE-FIELD DETERMINATION OF ISOCHROMATICS AND ISOCLINICS

Two correlative methods are developed for the computer-aided photoelas tic analysis of orthogonal 3D textile composites comprising 6 mm x 6 m m highly heterogeneous unit cells in-plane. The first method, presente d in Part 1, is used for the whole-field determination of isochromatic s and isoclinics; the second method, presented in Part 2, is applied f or subsequent photoelastic stress analysis. Part 1 delineates precisel y how one circular polariscope and two plane polariscope photoelastic images are implemented to extract the isochromatic parameter R and iso clinic parameter alpha using the digital image processing technique. T he photoelastic experiments were performed with orthogonal 3D textile composite as well as aluminum plates containing a hole under the uniax ial tension loading. The obtained values of R and alpha, for the case of the aluminum plate, are smoothly distributed over the field and sho w consistent agreement with those computed from finite element analysi s (FEM). In the case of the composite plate, the global distribution o f R and alpha also agree well with FEM results employing the homogeniz ed composite properties. However, both R and alpha exhibit local varia tions according to the 3D fabric structure, and the varying amplitude of alpha is relatively larger than that of R.