【摘要】 用 2 0kHz超声疲劳试验技术测试 40Cr钢、5 0车轴钢在 10 5～ 10 1 0 周次范围内的疲劳性能。结果表明 ,两种钢并不存在传统意义上的所谓“疲劳极限”。在超过 10 7周次 ,甚至 10 9周次的超长寿命范围内仍发生低应力疲劳断裂 ,其中 40Cr钢的S—N曲线呈现“连续下降型”特征 ;5 0车轴钢呈现“阶梯下降型”特征。对两种钢缺口试样的疲劳性能测试表明 ,缺口应力集中对疲劳性能的影响呈现“阶段性特征” ,在 10 6 ～ 10 7周次内存在一个临界疲劳断裂循环周次Nc,当疲劳断裂循环数Nf<Nc,随Nf 的增加 ,缺口应力集中对疲劳性能的影响程度呈上升趋势 ;当疲劳断裂循环数Nf>Nc,随Nf 的增加 ,缺口应力集中对疲劳性能的影响程度呈逐渐下降的趋势更多还原

【Abstract】 Fatigue behaviors of 40Cr and 50 steel between 10⁵ and 10¹⁰ cycles were tested by ultrasonic fatigue method at a frequency of 20?kHz. The experimental results showed that fatigue failure can occur even at amplitudes below the conventional fatigue limit in the ultra-long life regime of N>10⁷ cycles, and the conventional fatigue limit could not be obtained until 10⁹ cycles. A continuously decreasing S—N curve in 40Cr steel and a stepwise shape S—N curve in 50 steel was observed. The effect of notch stress concentration on the fatigue behaves shows a stage shape and exist a critical number of cycles N_c. If cycle number N_f<N_c, fatigue notch factor K_f increase with increasing number of cycles, whereas, if N_f>N_c, fatigue notch factor K_f decrease with increasing number of cycles.更多还原