不同循环载荷下54SiCr6钢的疲劳强度

对高强弹簧钢54SiCr6在3种循环加载条件下(旋转弯曲,超声和拉压)的疲劳性能进行了测试和比较.由于疲劳试样存在应力梯度和尺寸差异,3种循环载荷下对应的疲劳强度有较大差别.断口分析表明,3种疲劳样品也具有不同的断口形貌.通过计算高应力截面积,可以得到不同载荷下疲劳强度之间的定量关系,从而为评估不同载荷下的不同试样的高强钢疲劳强度提供依据.

FATIGUE STRENGTHS OF THE 54SiCr6 STEEL UNDER DIFFERENT CYCLIC LOADING CONDITIONS

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 σ_lim,0 and σ_ΞA 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.