FATIGUE STRENGTHS OF THE 54SiCr6 STEEL UNDER DIFFERENT CYCLIC LOADING CONDITIONS
不同循环载荷下54SiCr6钢的疲劳强度

Since ultrasonic fatigue test has been used to study the very high cycle fatigue (107—109 cyc), the difference between ultrasonic and conventional fatigue test methods should be evaluated in order to ensure the validity of ultrasonic fatigue result. By comparing some results of other researchers, it is found that the frequency effect is negligible, and the loading condition is the main reason for the difference. A comparison of the fatigue strengths of the 54SiCr6 high strength spring steel under three kinds of cyclic loading conditions, rotating bending (RB), tension compression (TC) and ultrasonic (UL), was reported. The results reveal that the three kinds of fatigue specimens display different fracture features, and the fatigue strength of RB is the highest, TC is the lowest, and UL is somewhere in between. The difference in the fatigue strengths is mainly attributed to the distinctions of stress gradient and the size of specimens. By taking highly stressed cross–section area (HSCA) into consideration, a relationship of the fatigue strength and loading condition was proposed, and the two constants σlim,0 and σΞA in the equation of HSCA are mainly dependent on material strength and inclusion size, respectively. A relationship of fatigue strengths between RB and TC is also discussed specifically.