Using Fatigue Analysis to Predict the Propagation of Internal and External Semi-Elliptical Cracks in Pipes Under Cyclic Load

This study presents a comparative fatigue analysis of crack propagation in both internal and external semi-elliptical cracks using the three-dimensional finite element method (FEM). Initially, the results were validated by comparing them to those of Raju and Newman, with a high degree of correlation observed. The study thoroughly examines and analyzes the influence of key parameters, such as the load ratio (R), geometry ratio (Rm/t), material properties, and crack size. In this study, capabilities and limitations of existing fatigue analysis code (e.g., direct cyclic approach with extended finite element method (XFEM)) in abaqus for low-cycle fatigue simulation are explored for pipelines assuming linear elastic material behavior. However, for real pipelines, an indirect cyclic approach is used based on the fracture energy parameters (e.g., J-integral) calculated using XFEM in abaqus. The power-law relationship (like Paris's law) is used to generate the fatigue crack growth curve. In addition, the Monte Carlo method is employed to assess the probability of structural failure. Two mathematical functions, a sixth-degree polynomial and a Gaussian function, are explored to evaluate the density distribution. The density function is produced by fitting the histogram to the primary theoretical models. The durability of pipes is determined by their mechanical characteristics.