High cycle fatigue life prediction model including the effects of prior cold work and surface residual stress

The high cycle fatigue (HCF) endurance limit of strain hardening materials is shown to be dependent on local values of residual stress and prior cold work. Empirical and numerical approaches to determining these local values are defined and demonstrated. These approaches are then used to establish an equation defining this dependence for a specific material, mean stress, and temperature.; Field data from high cycle fatigue failures of specific compressor tie bolts is used as a practical test case to validate application of the derived equation. It is also shown that the thread manufacturing process directly influences the thread fatigue capability by influencing the local residual stress and prior cold work. A key process parameter is strain rate. Empirical and finite element techniques demonstrate that the differences in strain rate between the rolling processes used in studs provided by two different suppliers result in different levels of prior cold work and residual stress in the threads. Fatigue diagrams are drawn for two thread rolling processes based upon measured thread and rolled plate data, and are shown to be consistent with field experience. A practical test is defined for qualifying acceptable thread rolling processes, using measured values of local Knoop microhardness. Finally, generic application of these methods to all strain hardening metals is indicated.; It is concluded that these same methods may be used for qualification of fatigue capabilities influenced by other component manufacturing or surface enhancement processes such as turning, shotpeening or burnishing.