Relationship of Crack Growth Between Thermal-Mechanical and Isothermal Low-Cycle Fatigue at Elevated Temperatures

The surface and through crack growth behaviors of some steels in thermal-mechanical and isothermal low-cycle fatigue at elevated temperatures were investigated. It was shown that the crack growth rate under each test condition was successfully correlated with the cyclic J-integral range by the simple power law equation, regardless of crack configurations and test controlling modes. Based on the results thus obtained, the relationship between the crack growth rates of the two types of fatigue was discussed. When the crack growth rates in thermal-mechanical and isothermal low-cycle fatigue at elevated temperatures were correlated with the parameter of which the range of cyclic J-integral was divided by the equivalent flow stress defined in this work, they could be represented by a single curve approximately. The crack growth rates in isothermal fatigue under various test temperatures could be also represented by the same single crack growth curve described above, regardless of the test materials. From the above result, it was found that the difference of crack growth rate in both types of fatigue merely resulted from the difference of equivalent flow stress.