An investigation of shear response of composite material systems

An investigation of shear response for various composite material systems is presented. The uniformity of the strain fields is studied experimentally and numerically for different specimen configurations. Conventional strain gage measurements and the moiré interferometry technique are employed to obtain information of actual deformation of the specimen. Based on the contour maps of displacement obtained from moiré tests, the localized hybrid method is used to quantify the magnitude and scale of the nonuniform deformation in the real strain fields. The finite element analysis is also performed for predicting the global nonuniformity of the strain fields. It is shown that the significant nonuniformity in shear deformation observed in experimental results can not be predicted by the existing analytical and numerical models. It is considered that the nonuniformity is primarily at a local level, which is associated with the material inhomogeneity. The implication of the local non-uniform deformation fields on the material property evaluation and failure prediction are discussed. The nonlinearity of shear response is investigated experimentally by performing strain gage and moiré tests. Curve fitting techniques proved to be a convenient and effective tool for characterizing the nonlinear shear response of composites. It is suggested that not only the initial shear modulus but also other coefficients of the fitting function be used for the evaluation of nonlinear shear behavior of a composite. The experimental results show that the nonlinearity has no significant effect on the shear strain distribution, verifying the validity of correction factors in the nonlinear range. Shear stress at a selected shear strain level is suggested as an engineering definition for shear strength of composites. The shear response of some novel composites is also investigated, the test results of which are presented.