20kHz和140Hz下高强汽车弹簧用钢的疲劳性能

摘要

The fatigue property of a high strength automotive spring steel was investigated via the con‐ventional fatigue testing and ultrasonic fatigue testing .The fatigue fracture surfaces are observed using SEM respectively .The results show that the characteristic of fracture surface of the specimen at 20kHz and 140Hz are similar ,i .e .for the specimen of fatigue lifetime within 106 ,the fracture are prone to initi‐ate from the surface .However for high cycle fracture(HCF) and very high cycle fracture(VHCF) ,the fracture are prone to initiate from specimen subsurface or internal inhomogeneities with a distinct feature of so‐called“fish‐eye” .For the VHCF ,there is a characteristic “granular‐bright‐facet(GBF)” area around the origination .Step‐wise S/N curve with a horizontal part was observed for the spring steel ,and the S/N curve character is related to the size of the inclusion .There is obvious difference of fatigue lifetime at 20kHz and 140Hz .i .e .the frequency effect of spring steel in the paper is obvious .%对一种高强汽车弹簧用钢分别进行了常规疲劳和超高周疲劳试验。常规疲劳试验频率为140Hz，超高周疲劳试验频率为20kHz。采用扫描电镜分别对失效试样进行断口扫描分析。结果表明，140Hz和20kHz下的疲劳断口表现出相似的特征，在106循环周次内失效的试样断口起源萌生于试样表面；而高周和超高周疲劳试样断口起裂于试样次表面或内部，且断口呈现“鱼眼”状特征。另外，超高周疲劳断口裂纹源周围存在粒状亮面特征区。弹簧钢的超高周疲劳S／N曲线呈现二次下降型特性，其S／N曲线的形态特征跟试样夹杂物尺寸密切相关。140Hz得到的疲劳试验结果与20kHz下的超高周疲劳试验结果有着明显的偏差，弹簧钢频率效应明显。