Crack-growth studies under selected temperature-strain histories

In many engineering applications, components experience complex temperature-strain histories. The sequence of exposure to temperature and strain, and their respective ranges as a function of time, influence the material behavior. The ensuing crack-nucleation and crack-growth behavior may be different than that predicted based upon simpler tests. A number of temperature-strain histories were considered in this study. Isothermal straining, out-of-phase thermomechanical loading and repeated temperature and strain cycle (termed "repeated cyclic strain aging") tests were performed on laboratory specimens of 1070 steel (Class U wheel steel). The differences in observed behavior among the three histories were discussed in terms of the crack growth rates. Repeated temperature and strain cycle histories resulted in highest crack growth rates on double-edge notched specimens. The two-bar structure was used to simulate temperature-strain histories typically experienced in service. By considering phase and amplitude changes in the temperatures of both bars, variations of the out-of-phase thermomechanical loading case were examined. The model was employed to understand mechanical strain-temperature variation under localized surface heating conditions.