Fatigue Crack Growth Analysis in Python algorithm with Finite Element Methods : Numerical Simulation of Fatigue Crack Growth

Abstract: The goal of this thesis was to construct and develop a python-based finite element computer program for the evaluation of fatigue crack growth rate in notched metallic rods. The simulation was done by implementing elastic stress theory and linear elastic fracture mechanics techniques. To assess the python script and also determine the factors affecting the growth rate of fatigue cracks, experimental testing was performed. A metallic rod made of steel with a single crack which was initiated with a hardness indent in the middle of the notch and fatigue crack growth testing was performed with the help of a servo-hydraulic tensile testing machine and a camera. The developed python script was used to perform two numerical analyzes with the help of the software suite ABAQUS. Two methods were then implemented to determine the crack growth rate. These methods are the Paris crack growth rate model and Walker’s crack growth rate model. It is concluded that the stress intensity range has a governing factor on fatigue crack growth. ABAQUS was used to determine the stress intensity range for each specific crack geometry. The obtained numerical results were compared with the experimental tests performed on the steel notched test specimens in Karlstad University's mechanical laboratory and also with each other. After analyzing the results, it was concluded that both numerical methods gave good results in the beginning and had a similar crack growth pattern where Walker's method was slightly better, but after the crack length exceeded about 0.5 mm, both began to deviate significantly from the experimental results.