Thermo-mechanical fatigue damage mechanism and life prediction of compacted graphite iron with high strength

Abstract

The thermo-mechanical fatigue (TMF) damage mechanism of typical compacted graphite iron with high strength (RuT450) was investigated in different temperature ranges. The results indicate that the TMF life decreases as the peak temperatures rise from 400 °C to 500 °C. As the cyclic number increases, the maximum tensile stress shows slight cyclic hardening in the temperature range of 100 to 400 °C. Additionally, in the temperature range of 100 to 500 °C, the maximum compressive stress exhibits slight cyclic softening. The fatigue damage and crack propagation processes demonstrate that the tearing of vermicular graphite at the edge of the sample is the primary cause for fatigue crack initiation in the lower temperature range. The weakening region comprised of multiple vermicular graphite particles facilitates the gradual extension of cracks. At higher peak temperature, oxidation rapidly erodes the interface between the vermicular graphite and the matrix, which leads to the debonding of graphite and initiation of the fatigue cracks. The rapid oxidation effect accelerates the corrosion of the metal matrix, promoting crack propagation, which is the primary factor contributing to the reduction of fatigue life. Given the complexity and high cost associated with the TMF test, a method for predicting the TMF life by building the correlation between low-cycle fatigue and the TMF lives in terms of the hysteresis energy is proposed. This method enables rapid and accurate prediction of the TMF life through a relatively small amount of samples and simpler experiments, demonstrating significant industrial application potential.