Fatigue crack propagation and closure behavior of modified 1070 steel: Finite element study

Abstract

A new finite element modeling methodology for simulating plasticity-induced crack closure is developed for the general purpose, commercially available, finite element code called ABAQUS. This new method utilizes substructuring techniques to maximize computational efficiency. This is achieved without sacrificing model accuracy in depicting the structural behavior of the specimen. Model refinement studies were conducted to establish guidelines for model parameters such as mesh density and element aspect ratio for the elements in the crack plane region. These techniques and guidelines were used to model a compact tension specimen and simulate a series of four tests conducted during the experimental portion of this study. Comparison of stationary crack and propagating finite element models revealed that plasticity-induced crack closure produces a significant amount of crack tip shielding. Such behavior effectively reduces the strain range and mean strain experienced at the crack tip. Direct comparisons between finite element model and experimental results were performed in terms of crack closure level, crack mouth opening displacement and surface strain gage data. These comparisons revealed excellent agreement. As a result of the study, use of an experimentally verified finite element technique in conjunction with fatigue crack growth experiments is suggested as a potential means of developing future crack growth rate models in terms of the traditional fatigue parameters of strain range and mean strain.