Study of crack growth in 3D using Elasto-Plastic Fracture Mechanics (EPFM)

Abstract

An elastic-plastic fracture mechanics (EPFM) procedure has been developed to analyze the crack initiation, stable growth, and instability in the plane stress condition. The design is based on the Dugdale Barenblan strip yield model but modified for strain hardening and stable crack growth under monotonic loading. The J integral is used as the crack growth criterion in the model. Some gas turbine casings are very susceptible to involve cracking in critical points. According to studies, thermal fatigue is specified as the main reason for the creation of cracks. This approach is to predict the fatigue life of the detected crack on the edge of the eccentric pinhole of a heavy duty gas turbine casing, which is one of the most probable positions for crack initiation and propagation. Today, assessments of cracks and crack growth are done. The implementation of a new fracture mechanics-based approach to analysis may significantly extend equipment life while improving model accuracy and system reliability. Stress distribution of the casing was calculated in accord to engine work cycle, and then fatigue crack growth was predicted by EPFM parameter J integral. The analysis results showed that the crack growth rate would decrease gradually, and after periods of time, while stress intensity factor values will reach the Threshold value, the crack propagation will stop. J-Integral methods were implemented for calculating the fracture mechanics quantities, and the Paris model was used to estimate the fatigue life.