Phase field fracture modeling of fatigue crack growth and ductile damage

Waseem, Sarim
The modeling of fracture is a computationally challenging task due to the inherent discontinuities involved. The characteristic features of the phase field methodology circumvent these limitations through a diffuse interface approach to crack growth. In this thesis, the phase field approach to brittle fracture is expanded to cover both fatigue and ductile fracture based on the existing methodologies described in the literature, with some novel features added to simulate more complex behavior. Two fatigue models are simulated with additional features in both designed to capture the crack growth retardation phenomenon, which has previously not been studied in a phase field framework. For one, the fatigue damage accumulation algorithm is al tered to include a damage threshold. This is done to simulate crack closure effects and by extension, crack growth retardation effects due to overload. For the second model, a temporal fatigue damage accumulation system based on a representative load is simulated, additionally incorporating a zone based crack retardation mecha nism that responds to single cycle overloads. These features allow both models to more realistically simulate complex variable amplitude loading cases restricted to the tensile region. The fatigue models are found capable of simulating crack growth re tardation in the wake of applied overloads, with varying levels of success in matching experimental results. A third phase field model is used to simulate failure due to plastic deformation. A classical phenomenological uncoupled damage model is incorporated into a phase field ductile failure framework to allow it to accurately capture plastic damage evo lution in complex stress states as well as allow more precise calibration. A damage threshold is applied to control the evolution of damage around the critical failure strain. The model is able to reproduce experimental load-displacement responses, plastic deformation and crack patterns for the given parameter set for various bench mark specimens.
Citation Formats
S. Waseem, “Phase field fracture modeling of fatigue crack growth and ductile damage,” M.S. - Master of Science, Middle East Technical University, 2023.