INVESTIGATION OF THE MECHANICAL BEHAVIOUR OF MMCs USING FINITE ELEMENT METHOD

Abstract

During the loading of the fiber reinforced Metal Matrix Composites, the debonding of the interface plays a critical role in overall composite behaviour. The process of the debonding can be represented as independent decohesion in two directions, along the length of fiber and normal to the fiber surface. In order to model this behaviour, an axisymmetric cylindrical model is presented with the objective of evaluating the interfacial properties of wire reinforced tungsten matrix composites. Commercial tungsten wire reinforcement, a matrix of tungsten and the copper interface, with 40 % volume fraction is chosen as the model material. The interface is modeled using the cohesive layer concept, in addition to the elastic parameters; a damage criterion based on the maximum nominal stress is also defined for the interface. The finite element method has been used for analysis in transverse loading direction, with a basic unit cell of two quarter fibers embedded in matrix. The fiber, matrix and interface properties are similar to those in axisymmetric cylindrical finite element model. This gives useful insight into the factors affecting transverse properties of these materials. To gain insight into mechanism at work during normal debonding, interface model was examined for two matrix material behaviours: elastic and elastic-perfectly plastic matrix. The simulation results are in good qualitative agreement with experimental results in context of the load—displacement graph for axisymmetrie cylindrical finite element model. Debonding of the interface starts at the bottom of the specimen due to tensile stresses caused by bending of specimen. Further, the decohesion starts around each fiber, in the region where the interface is perpendicular to the applied load during the transverse loading. However, modeling the stepwise debonding requires the more sophisticated implementation of interface behaviour concerning the interface thickness and friction between wire and matrix.