Evaluation Of Thermo-mechanical Fatigue Life Of 20g Under Complex Stress State

With the modern industry development into high-speed, high-temperature and high-pressure, fatigue problem is threatening the safety of the equi pments. Statistics shows that eighty percent components' crack failure is caused by fatigue. Since the equipments are worked under execrable surrou ndings in a long term, especially cokedrum, which is most important asse mbly in petro-chemical industry, are worked under a cycle of temperature from normal temperature to 480℃, with hydraulic pressure cycle and air pressure cycle at the same time. All the working conditions causes stress failure, consequently, unexpected grave accidents.TMF(thermo-mechanical fatigue) under complicated stress, which is the most complex part in high temperature fatigue study, involves strain cycle load, temperature cycle load, creep cycle load and surrounding effects. Its mechanism is not clear, or its physical and mechanical model without a uniform conclusion. So this research is of practical and academic signify -cance.Comparing different gap, different strain range, different strain rate and the influence on TMF total life according to TMF tests for 20g, calculating stress and strain with relevant test results using FEA software, finding the dangerous part in the sample and -selecting proper factors to denote TMF total life, the educing function is present.Differing to usual function considering strain range as the only inf -luential factor, a experiential equation, which taking strain rate into account, is discussed at last.