Residual Service Life of a Wheelset Axle with Surface Transverse Crack
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RESIDUAL SERVICE LIFE OF A WHEELSET AXLE WITH SURFACE TRANSVERSE CRACK V. R. Skal’s’kyi,1 D. V. Rudavs’kyi,1,2 R. Ya. Yarema,3 V. R. Bas,3 and Yu. I. Kanyuk1
UDC 539.4
A new procedure for the numerical evaluation of the residual service life of a wheelset axle is proposed. The procedure is based on the kinetic equation of fatigue crack growth obtained within the energy approach of the fracture mechanics of materials. It is shown that relatively small cracklike defects on the surface of the axle attain their critical sizes after a relatively short run. It is shown that, under given loading conditions, the residual service life of the wheelset axle weakened by a surface crack depends not only on the initial area of the crack but also on the geometry of the crack front. Keywords: wheelset axle, surface fatigue crack, stress intensity factor, residual service life.
Wheelset axles are among the most crucial elements of the undercar in the railway transport. In recent years, the number of events of the fatigue fracture of axles in the course of operation of freight cars significantly increased (Fig. 1). This is explained by the gradual accumulation of fatigue microdefects in the material of axles under the action of cyclic loads in the process of motion of the train. Under the action of high operating bending moments, the surfaces of the axles turn into the most loaded place and its various microdefects (microcracks, dents, welding burns, etc.) play the role of additional concentrators of already high mechanical stresses. These (as a rule, technological) microdefects serve as potential sites of the initiation and propagation of fatigue cracks, which may lead to the complete failure of the axle in the course of motion of the railway car with severe catastrophic consequences. Therefore, the purpose of the present study is to develop a method for the evaluation of the residual service life of the wheelset axles (of freight cars) with cracklike defects revealed on the surface. Substantiation of the Method of Investigations The problem of fatigue fracture of wheelset axles was investigated in numerous works (both in Ukraine and abroad) [1–5]. However, there are no methods with the help of which the residual service life of these metal structures can be estimated by using the most efficient energy approaches of the mechanics of fatigue fracture. Most frequently, the shapes of the defects observed on their surfaces are close to semielliptic cracks (Fig. 2). Thus, in what follows, we construct a solution of the problem of evaluation of the residual service life of a wheelset axle weakened by a semielliptic crack formed on the surface of its middle part (Fig. 3a). 1 2 3
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected].
Private Joint-Stock Company “Lviv Locomotive Repair Plant”, Lviv, Ukraine.
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 52, No. 4, pp. 40–45, July–August, 2016. Original article submitted March 15, 2016.
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