Finite element simulations of fatigue crack growth and closure

A modified elastic-plastic finite element program was used to simulate fatigue crack growth and closure. The study has identified some of the factors that contribute to crack closure. It has provided an evaluation of stress, strain and displacement fields near crack tips and their contribution to crack closure. The thesis contains three parts:In the first part, the mechanism of crack closure under plane strain condition was explained. It is identified that material ahead of the crack tip contracts in the transverse direction, and this mechanism provides residual material on crack surfaces to cause crack closure. Stress-strain history and material displacements as the crack advances are presented to support this model.In the second part, a distinction is drawn between residual stresses in the absence of crack closure and those due to plasticity induced closure. A new crack tip parameter, S$\sb{\rm tt}$, is defined as the applied stress level corresponded to the development of tensile stresses immediately ahead of crack tips. The results demonstrated the importance of this parameter, as the stresses ahead of crack tips could remain compressive even when the crack surfaces opened.The notch effect on crack closure is studied in the third part of the thesis. Crack opening levels were obtained for crack growing from notches. A set of closure prediction equations was proposed to determine crack growth rate from notches for variable notch shape, applied maximum load level, R ratio and crack length from notch roots on different materials. The model has applied to a steel and an aluminum alloy, and the prediction of crack growth rate from notches were very satisfactory.U of I OnlyETDs are only available to UIUC Users without author permissio