A Cosserat continuum model for layered materials

Modelling the behaviour of materials consisting of a large number of layers is often required in geomechanical applications. In this study, an equivalent continuum model suitable for describing the mechanical response of such layered materials is considered. The model is based on the Cosserat continuum theory and incorporates the moment (couple) stresses in its formulation. The layers are assumed to have equal thickness and equal mechanical properties with elastic behaviour. In contrast to the earlier Cosserat models, the possibility of layer interface (joint) plastic-slip as well as tensile-opening during loading is considered. The importance of moment stress in describing the behaviour of such materials is discussed and highlighted through an example. It is shown through numerous examples that when there is a possibility of inter-layer slip and subsequent layer bending, equivalent continuum models based on the conventional anisotropy theory may not represent a true response of the layered materials. The relationship between the large-scale (Cosserat) description of the layered material and the fine-scale (micro) description of the stress-strain state of an individual layer is determined. The model is incorporated into the finite element (FE) code AFENA and several examples of load-deflection problems in layered materials are analysed. The Cosserat model is verified against the explicit joint FE model. Comparison between the two models shows a remarkable agreement suggesting that the Cosserat model is capable of providing an accurate prediction of the load-deflection behaviour of layered materials. (C) 1997 Elsevier Science Ltd.