FATIGUE STRENGTH AND RESIDUAL LIFETIME ASSESSMENT OF RAILWAY AXLES SUBJECTED TO FOREIGN OBJECT DAMAGE

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.