MICROMECHANICAL MODELING OF THREE PHASE COMPOSITE AXISYMMETRIC SYSTEM USING A VARIATIONAL METHOD

Abstract

In this study, a theoretical framework is presented for the analysis of interfacial/interphasial stresses in a three-phase axisymmetric composite system subjected to thermal or thermomechanical loads. This composite system consists of a cylindrical fiber embedded in a matrix having an interphase between them. Analytical models are presented based on a variational principle which minimizes the complementary energy in the composite system. The problem is formulated by assuming stress functions which satisfy the equilibrium equations. Incorporating the traction-free boundary conditions and the stress continuity conditions at the interfaces, all the stress components in the fiber, interphase, and matrix are expressed in terms of two unknown functions. Minimization of energy in the system leads to two coupled integro-differential equations. The problem has also been computationally studied by using Abaqus FEA. Initially, an analytical model is developed to predict stresses in a system having a homogeneous interphase subjected to fiber pull-out mechanical load. Stresses in the interphase/interfaces predicted by the above model are in good agreement with the finite element predictions. Secondly, another analytical model considering inhomogeneous interphase (having varying elastic properties as a function of radius) is developed and validated by the corresponding computational model. Computational models which account for variation of elastic properties along the radius of interphase are developed using Abaqus FEA through a user written subroutine called UMAT. Subsequently a group of analytical and computational models have been developed to predict the residual thermal stresses in the composite system considering both inhomogeneous and homogeneous interphase. It has been observed that the stress peaks in an interphase graded system is less than those of ungraded interphase composite system. Stress analyses of both analytical and finite element models indicate that structural performance of the composites can be optimized by designing interphases. Experimental results of 3D printed three phase composite system have been found to be in line with the predictions of the theoretical models and open up a new avenue for engineered design of interfaces and/or interphases in composite materials using 3D printing technology.

Date of Award	2014
Original language	American English
Supervisor	Kumar Shanmugam (Supervisor)