超高周疲劳裂纹萌生和初始扩展的机理与模型

提出了高强材料超高周疲劳值得关注的若干关键问题,探讨了高强钢超高周疲劳裂纹起源和初始扩展的特征与机理。文中通过大量实验结果,显示了"鱼眼"和"细晶区"尺寸随疲劳寿命的变化趋势,表明"鱼眼"和"细晶区"的应力强度因子值不随疲劳寿命变化而是基本

金属材料超高周疲劳行为的Monte-Carlo模拟

基于Tanaka-Mura的微观位错模型并结合结构可靠性及灵敏度的统计理论,采用MATLAB自编程序对金属材料S-N曲线的分散特性进行了Monte-Carlo模拟分析,并对比了SUJ2钢的旋转弯曲疲劳实验数据,最后根据结构可靠性灵敏度理论分析了超高周疲劳失效概率的各影响因素的敏感性

应力比对疲劳裂纹扩展速率和疲劳强度的影响

研究了不同应力比R下近门槛区裂纹扩展速率之间的关系,表明应力比R对近门槛区裂纹扩展速率和裂纹稳定扩展区裂纹扩展速率的影响可以表示成统一的形式,即da/dN=C(△K_(eff)-△K_(c th,o)~m,其中△K_(eff)=△K(1-R)~(-α)或△K_(eff)=(K_(max)~α(△K~+)~(1-α),△K_(c th,0)为裂纹萌生门槛值,C,m,α为与材料有关常数。进而,推导了应力比(平均应力)对疲劳强度的影响关系,并与文献中的实验结果(包含

Very high cycle fatigue for GCr15 steel with smooth and hole-defect specimens

Very high cycle fatigue (VHCF) properties of a low temperature tempering bearing steel GCr15 with smooth and hole-defect specimens are studied by employing a rotary bending test machine with frequency of 52.5 Hz. Both smooth and hole-defect specimens break in VHCF regime with some difference in fatigue crack initiation. For smooth specimens, a fine granular area (FGA) is observed near the grain boundary in the fracture surface of the specimens broken after 10^7 cycles. But no FGA is observed in the hole-defect specimens broken in VHCF regime, and the VHCF crack does not initiate from the small hole at the surface as it does at low or high cycle fatigue regime. Internal stress is employed to explain the VHCF behavior of these two types of specimens. At last, an advanced dislocation model based on Tanaka and Mura model is proposed to illustrate the internal stress process and to predict fatigue crack initiation life with FGA observed in the fracture region.Very high cycle fatigue (VHCF) properties of a low temperature tempering bearing steel GCr15 with smooth and hole-defect specimens are studied by employing a rotary bending test machine with frequency of 52.5 Hz. Both smooth and hole-defect specimens break in VHCF regime with some difference in fatigue crack initiation. For smooth specimens, a fine granular area (FGA) is observed near the grain boundary in the fracture surface of the specimens broken after 10^7 cycles. But no FGA is observed in the hole-defect specimens broken in VHCF regime, and the VHCF crack does not initiate from the small hole at the surface as it does at low or high cycle fatigue regime. Internal stress is employed to explain the VHCF behavior of these two types of specimens. At last, an advanced dislocation model based on Tanaka and Mura model is proposed to illustrate the internal stress process and to predict fatigue crack initiation life with FGA observed in the fracture region

Reliability analysis of very-high-cycle fatigue crack initiation for a high strength steel

A high carbon chromium steel was tempered at 150℃,180℃,and 300℃to form three groups of specimens,and veryhigh -cycle fatigue(VHCF) tests were performed via rotating bending to investigate scatter properties of S-N curves. Experimental results show an increasing tendency of life scatter with the i..