Stress Intensity Factor of Thermal Fatigue Crack under Cyclic Loading

To reveal the rule of effect of cyclic temperature loading on the stress intensity factor of thermal fatigue crack,the stress-strain of crack tip under various cyclic loadings and the stress intensity factor of thermal fatigue crack are calculated by using finite element method in consideration of the multi-linear plastic kinematic hardening characteristic of a material.The stress intensity factor is dependent on the accumulation of plastic compression strain,which is sensitive to temperature loading sequence.Thus,the stress intensity factor is influenced by the temperature loading sequence,too.If crack propagation is not considered,the stress intensity factor of thermal fatigue crack will not change with cycles on condition that temperature amplitude is constant.However,when the temperature amplitude is variable,the low temperature cycle will not affect the stress intensity factor of latter high temperature cycles,but high temperature cycle will affect the stress intensity factor of latter low temperature cycles,and make it equal to that of high temperature cycle.Thus,a burst high temperature loading will badly threaten the lives of high temperature components.The thermal fatigue crack propagation testing proves that the calculated result by finite element method is correct.