FAILURE ANALYSIS OF INTERPENETRATING PHASE COMPOSITES BY ELEMENT FREE GALERKIN METHOD

Abstract

Interpenetrating Phase Composites (IPC) can be defined as multiphase composites in which each phase is three-dimensionally interconnected throughout the structure. The unique geometry of the reinforcement offers improved combination of mechanical and physical properties. They are lighter, stiffer, stronger and tougher material. Based on the occurrence of interpenetration at different length scales, interpenetrating phase composites can be classified as molecular, micro or meso varieties. This project gives a detailed description of the failure analysis of these fascinating new materials. The computational tool developed to model and simulate mechanical behaviour of IPC is based on Element Free Galerkin Method, and is developed in MATLAB. Due to complexity in microstructure and randomness in behaviour of IPC, the modelling of these materials has not been sufficiently studied so far. Two models have been proposed in this thesis. The unit-cell model is based on the geometry of a sub-cell. A sub-cell is a collection of randomly generated rectangles placed in the corners of a square. Many sub-cells arranged together makes a unit-cell. The random microstructure model is based on selection of the position of reinforcement particles in the matrix. A probability scheme is applied for the selection of the particles. A term called degree of interpenetration is introduced which controls the geometry of the models between interpenetrating and particulate nature. All the influencing parameters have been modelled like volume fraction, interpenetrating geometry, etc. Two types of analysis is carried out in both these models. The elastic analysis includes finding out the equivalent elastic properties of the IPC, like Young's modulus, shear modulus and Poisson's ratio. This has been carried out using effective medium approximation technique where the strain energy of the IPC is equated to that of the equivalent homogeneous medium. The elastic properties are found out for all volume fractions at different degrees of interpenetration and is also validated through experimental results. The elasto-plastic analysis is carried out to find the equivalent stress-strain curve of IPC for large values of strain. The nonlinear curve has been modelled using the Ramberg-Osgood material model. A progressive damage model is carried out to simulate the failure of IPC. The strength and 0.2% proof stress of IPC is higher than the particulate composite. The resultant stress-strain curves are validated through experimental results for both the models.