بررسي تجربي تاثير تنش متوسط كششي بر رفتار تناوبي فولادهاي متخلخل تف جوشي شده حاوي نيكل

INVESTIGATION OF TENSILE MEAN STRESS EFFECT ON FATIGUE BEHAVIOR OF POROUS SINTERED Ni STEEL

The demand for lower production costs and unique advantages resulted in the use of PM materials even for highly stressed fatigue loaded components. Behind of microstructure, mean stress, as a most important fatigue loading parameter, has a strong effect on cyclic performance of sintered steels. In present study, the effect of mean stress on fatigue behavior of diffusion-bonded, Distaloy AE, powder metallurgy low alloy steel was investigated. Axial fatigue tests were performed on standard samples of this steel with two carbon contents and in a range of tensile mean stresses. On principle the fatigue life is shortened by tensile mean stress. Microstructural investigations reveal that for tensile mean stress pores are widened and linked up by cracks. Moreover fractography evaluation on fatigue fracture surface indicated the multiple fatigue cracks initiation sites with increasing the tensile mean stress. Evaluation of experimental results and plotted curves propose criteria, that with use of this, we can predict endurance fatigue limits of this steel in non zero mean stress conditions.