The Effect of Temperature on the Fatigue Damage of Steel

The object of the present research is to investigate the effect of temperature on the fatigue damage of steel.Two kinds of killed steel have been used in the experiments; (e.g. 0.12% C and 0.18% C), all of them were sufficiently treated to reduce the free carbon and nitrogen and thus minimize the strain aging effects.Testing temperature on the fatigue tests was 0∼100°C, and the testing machine used was a cantilever type rotary bending one of 3000rpm.For the purpose of investigating the effect of temperature the magnitude of the microplastic stress-strain hysteresis loops were measured through all stages of fatigue process (the process can be divided into three stages) by wire strain gauges 3mm length.From these experimental results, we have got the following conclusions:(1) The microplastic hysteresis energies at high temperature were smaller than at low temperature, and the fatigue lives were shorter at high temperature.(2) Effect of the temperature on the fatigue lives varied at every stage of the fatigue process and according to the kind of the method of temperature changing.(3) Among the results obtained at constant stress amplitude the following relation is found.Nf∝U∝exp(const./T)where: Nf is fatigue life, U is the sum of hysteresis energy and T is testing temperature (in deg. Kelvin), (4) The empirical relations obtained for the fatigue fracture has shown that the posibility of the prediction of fatigue life by non-destructive method is opened up by measuring the microplastic hysteresis loops on the fatigue process.