异物致损铁道车轴的疲劳强度及寿命评估
FATIGUE STRENGTH AND RESIDUAL LIFETIME ASSESSMENT OF RAILWAY AXLES SUBJECTED TO FOREIGN OBJECT DAMAGE
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摘要: 车轴是高速列车关键承载部件, 承受着源自车体、轨道的各种载荷,其疲劳行为直接关乎列车运行安全. 疲劳裂纹往往具有较强的隐蔽性和突然性,由车轴断裂发生的列车脱轨事件具有灾难性,因此确保车轴在运行中不发生失效事故, 对高速列车可靠运行至关重要.高速列车实际运营中, 车轴外表面受到各种异物击打, 会形成深度达毫米级的缺陷,破坏车轴表面完整性, 严重威胁车辆安全.本研究采用空气炮装置预制合金钢车轴小试样异物致损(foreign object damage, FOD)缺陷,采用扫描电子显微镜和体视显微镜观测损伤特征.开展高周疲劳试验获得光滑试样和FOD损伤小试样的疲劳S-N曲线,考虑载荷模式、表面质量和尺寸系数推证出全尺寸车轴的疲劳性能.断口分析表明, 裂纹于FOD附近多处位置萌生, 并在不同平面内连续扩展,最终汇聚为一个半椭圆形裂纹. 基于Peterson公式和El Haddad模型估算异物冲击速度100 m/s和138 m/s试样的理论疲劳极限远低于试验结果, 过于保守; 同时也远低于标准推荐值, 偏于危险. 最后,采用修正的Miner理论公式估算含FOD实物车轴的服役寿命,满足最低25年的服役寿命.Abstract: As the key load-carrying component of high-speed vehicles, theaxle bears various loads from both body and track, the service performanceis directly related to the high-speed railway safety. On account of the fatigue crack is often concealed and sudden,the train derailment caused by axle fracture is catastrophic. Therefore, itis very important for the safe and reliable operation of high-speed railwayto ensure that the axle does not break suddenly during operation. Foreignobject damage (FOD) larger than millimeter frequently happens during therunning of high-speed railway axles, causing damage to the surface integrityof the axle, which significantly induces the safety problem. In the present study, by using a commercial compressed-gasdevice, foreign object damage was prepared on alloying steel specimens fromhigh-speed railway hollow axles. The damage features were thenobserved using the stereomicroscopy and scanning electronic microscopy (SEM). Thefatigue S-N curves and fatigue limits were acquired for smoothed and FODedspecimens under high cycle fatigue (HCF) experiments. In view of the loadvariation, surface quality and size between the small-sizedspecimens and full-scale axles, the fatigue properties of FODed specimenswere modified to deserve the fatigue performance of full-scale axles.Through the fracture surface analysis, it was found that the multicrack initiations occurred in the FOD crater, and the cracks propagatedcontinuously in different planes to converge into a semi-elliptic crack.Besides, theoretical fatigue limits from Peterson formula and ElHaddad model under two impact velocities (100 m/s and 138 m/s) were moreconservative than those of experimental value and also far from standard value, showing an over dangerous design. Finally, the service life of FODed axlescalculated by the modified Miner formula can satisfy the 25years design lifetime of high-speed hollow axles.