Life prediction for mechanical components experiencing multiaxial fatigue, including effects of stress concentrations

This dissertation investigates fatigue life prediction for mechanical components subjected to multiaxial cyclic loading. Firstly, crack initiation life prediction is considered with an emphasis on recently-developed approaches, in particular, critical plane and plastic strain energy-based approaches. Traditional approaches and their limitations are also reviewed. A wide range of test data are used to evaluate the advantages and drawbacks of the recent approaches. A total strain energy-based method is proposed as a new approach, which takes into account effects of stress-state and mean stresses. Predictive capabilities of the different approaches are compared and discussed.; Secondly, prediction of surface crack growth is considered, especially under elastic-plastic straining conditions often encountered in low-cycle fatigue. Traditional ΔK and ΔJ approaches and their limitations in this fatigue regime are discussed. Two critical plane-based strain intensity factor range models and a newly-proposed cyclic plastic work model are compared based on correlations with limited available test data. Strong and weak points of the approaches are pointed out. The possibility of using the total strain energy density as an approach for predicting crack growth is also discussed.; Finally, an experimental study of the high-cycle biaxial fatigue of a notched specimen is conducted. Solid round bars of 1%Cr-Mo-V steel having a circumferential semi-circular groove are tested under fully-reversed constant-amplitude combined bending and torsion, in-phase and 90° out-of-phase. Smooth specimens of the same material are also tested under bending as well as torsion for baseline data. Crack growth behavior at the notch is described. Fatigue life data observed in the tests are used to evaluate the high-cycle multiaxial fatigue life prediction approaches evaluated earlier in the dissertation for smooth specimens. SAE 1045 steel notched specimen biaxial fatigue data are also used to evaluate the low-cycle multiaxial fatigue life prediction approaches.