Direct identification of the damage behaviour of composite materials using the virtual fields method

In the present work the virtual fields method (VFM) has been used to extract the whole set of material parameters governing a nonlinear behaviour law for composite materials. The nonlinearity considered here is due to the damage inherent to the in-plane shear response. The identification method is performed by applying the principle of virtual work knowing the whole strain field onto the surface of a tested specimen. The test chosen here is a shear bending test using a rectangular coupon loaded in a Iosipescu fixture. To illustrate the capabilities of the method, the identification is performed on data provided by finite element simulations. First, the nonlinear finite element model is described. Then. numerical aspects of the VFM are discussed, in particular the stability of the technique with respect to noise in the data. Finally, first elements of test optimisation are given by studying the effect of the length of the active area and the effect of the material anisotropy. This work contributes to the development of the VFM as a tool adapted to the processing of full-field measurement to identify parameters from general constitutive equations. (C) 2004 Published by Elsevier Ltd.