Failure criteria for functionally graded materials and application of GTN model using finite elements

Abstract

Functionally Graded Materials (FGMs) are special composites with a point to point continuous property variation. In this failure of laboratory scale FGMs is modeled using Gurson - Tvergaard -Needleman (GTN) model. Stress, energy, strain based (e.g. MTS, G, S criteria) and cohesive zone models that are used for failure modeling of FGMs are reviewed. GTN model originally used for failure of homogeneous materials is studied in detail. Because it is extremely difficult, if not possible, to obtain a closed form GTN yield function for a non homogeneous material, numerical implementation of GTN model is considered, and Abaqus is used for computational analyses. The validity of results are first checked by resolving a problem from literature using Abaqus. GTN model is numerically implemented to two different FGM specimens to study and predict failure. One of the FGM specimens is titanium monoboride / titanium (TiB / Ti) single edge notched bending (SENB) specimen, and the other one is a gradually ultraviolet irradiated polyethylene carbon monoxide (ECO) co-polymer single edge notched tension (SENT) specimen. It is concluded that GTN model is promising for failure simulations of FGMs with a proper selection of model parameters.