Reliability Analysis On A Non-powered Wheelset Of Railway EMU

Reliability analysis is carrieded out for a typical non-powered wheelset of EMU. Considering the multi-interference fits between wheel-axle-brake plates-bearing-axlebox in the wheelset and the physical wheel-tract contact relation out of wheelset, a finite element (FE) method integrated modeling is constructed for the wheelset, in which the bearing is replaced using its virtual form with an equivalent stiffness to the true bearing, so that the incompatibility is overcome between the macro-contact models of multi-interference fits and the micro-contact models of rollers-raceways in the bearings and and the FE method is feasible for the wheelset. Further, the following reliability analysis is carried out to the wheel and axle under using related integrated calculations to the wheelset:(1) Probabilistic assessment is performed for extreme mechanical strength check. Stresses are obtained for the wheel and axle by the AAR S 660 coded critical mechanical loadset. A probabilistic assessment is made by the probabilistic material mechanical properties. Results reveal that critical location of the axle is at the inner of wheel seat. Critical location for the wheel is at the start point of transition curve from inner web to rim of the wheel. But their reliability levels are both greater than 0.9999 with a confidence 97.5 percentage.(2) Probabilistic assessment is tried for fatigue durability strength check. Stresses are calculated by the EN 13979-1 coded three kinds of loadsets including train runs on straight line, curved line, and switch piece, respectively, and the corresponding braking cases. Combining the materials-to-structured fatigue durability properties, a probabilistic assessment of fatigue durability is performed to the wheel and axle, respectively. Results show that critical runing operation for the axle is at braking case on curved line and critical location is similar to extreme mechanical strength checking case at the inner wheel seat. But reliability level is greater than 0.9999 with a confidence 97.5 percentage. For the wheel, both assessment methods of radial stress amplitude and principal stress amplitude are applied. Critical runing operation is both at braking case on curved line and critical location is both at the start point of transition curve from outer web to rim of the wheel. But reliability levels are all greater than 0.999 with a confidence 97.5 percentage.(3) Spectral load based reliability analysis is explored for the wheel and axle. Spectral stresses of the wheel and axle are estimated using the regression equation of squeres ploynomial, which is used for converting the loadset of wheelset to local stress of wheel or axle. The ploynomial comes from regression to the stress data of 2n+l times FE integrated calculations using the loadset of spectral load sequence, where n represents the number of active loading elements for the wheelset. A piece of spectral load sequence for the wheelset from on-line inspection is used for the present explortation. Results give that critical location is still at the inner wheel seat for the axle. Reliability level is greater than 0.999 at a confidence of 97.5 percentages and expected fatigue life of 4,000,000 km. Cyclic shear stressing is the key element to result in fatigue damage of the wheel. Different from the above design fatigue strength check, present critical location for wheel web is at start point of the curved line from outer web to gub. Inner bound of the hub hole is critical location for the wheel hub. But the above locations hold reliability levels greater than 0.999 at the confidence of 97.5 percentage and the expected life of 4,000,000 km. What most valuable noted is that the tread sub-face of 1.5 mm deepth holds a maximum equivalent shear stress amplatude to result most possibly in spalling of surface lay material from the tread. The cracking life for this spalling start is lower that 600,000 km at confidence of 97.5 percentage and expected reliability of 0.99.The present work provides a basis for guiding stress calculation, design improvement and service management of the wheelset.