Viscoplastic response of multiphase composites using a strain-compatible volume-averaging method

The strain-compatible volume-averaging method, a recently developed micromechanical method for the analysis of multi-phase composites, is extended here to deal with viscoplastic behavior. Specifically, the method is applied to the problem of finding the viscoplastic response of a boron–aluminum unidirectional composite. A unified Bodner–Partom viscoplasticity model is used to model the inelastic behavior of the aluminum matrix of the composite. The inelastic response is obtained for different loading conditions and for several different fiber architectures. The influence of the loading orientation on the viscoplastic response of the composite is investigated using the strain-compatible volume-averaging method and the widely utilized generalized method of cells. It is shown that the response predictions of the strain-compatible volume-averaging method are invariant with respect to coordinate transformations while those of the generalized method of cells are not. This is due to the fact that the new method accurately models shear-coupling, a feature that is absent in the generalized method of cells. The results obtained with the new method are also compared with those of the finite element method. As far as the effective response of the composite is concerned, it is found that the results of the strain-compatible volume-averaging method are in good agreement with those of the other two methods. It is found however, that the computational cost of each of the three methods is proportional to the accuracy of the microstress field as might be expected.