K and J-Integral Approach for Fatigue-Creep Crack Growth Studies

Abstract

Fracture mechanics principles are being applied to understand the failure behavior of components subjected to fatigue loading at elevated temperature. Linear elastic and elastic-plastic parameters such as K and J-integral are normally employed. At low temperature and higher frequency of loading, stress intensity factor K can characterize the material behavior. At higher temperature and low frequencies, time-dependent effects will come into play. Crack growth models have been developed to characterize the material
behavior incorporating linear and nonlinear parameters. No clear-cut limits for the application of different parameters are established. There is a lack of experimental data for the whole range of temperature at which the components are supposed to function.

1. INTRODUCTION
In the present day, fracture mechanics principles are applied to understand the fatigue behavior of materials subjected to different types of loading and environments. Fatigue behavior is characterized in terms of fatigue crack growth parameters such as Δ K, Δ J
and C*. When the temperature is lower than the homologous temperature, the effect due to creep is very small, the crack tip stress field is dominantly elastic, and fatigue behavior can be studied using Δ K. But at elevated temperature, as time passes, the
uncracked ligament will become plastic. Elastic-plastic parameters such Δ J has to be used for characterizing crack growth. To characterize the fatigue behavior for the whole range of operation of components, equations have been developed combining different fracture mechanics parameters. In this paper, we present different fracture mechanics methodologies available for characterizing fatigue creep behavior of metallic materials.