Brittle Fracture Characteristics of a Thick -Walled Cylinder with an FGM Coating at the Inner Surface

Abstract

This study is concerned with the brittle fracture characteristics of a thick-walled cylinder with a functionally graded material (FGM) coating at the inner surface having two diametrically opposed edge cracks. First, the uncracked cylinder with the FGM coating is homogenized by simulating the nonhomogenous material properties with an equivalent eigenstrain. The homogenized cylinder is then considered to have two diametrically-opposed edge cracks for the analysis. Second, the cracks in the homogenized cylinder are represented by continuous distribution of edge dislocations. Representing the cracks by continuous distribution of edge dislocations, a method is then formulated to calculate the stress intensity factor (SIF), which is used to evaluate apparent fracture toughness of the cylinder. Also, the method is applied to the inverse problem of evaluating optimum material distribution intending to realize prescribed apparent fracture toughness in the cylinder with an FGM coating. For numerical results, a thick-walled cylinder with TiC/Al2O3 (Titanium carbide and Aluminium oxide) FGM coating at its inner surface is considered. The effects of material distribution profile, cylinder wall thickness, application temperature, coating thickness (CT) and number of cracks on both the apparent fracture toughness and stress intensity factor are investigated in details. It is found that all of these factors play an important role in the fracture characteristics of the thick walled cylinder with FGM coating. The numerical results of inverse problem reveals that the apparent fracture toughness in a thick-walled cylinder with an FGM coating depends significantly on the material distributions, and can be controlled within possible limits by choosing an optimum material distribution profile.