Kaniuk Y. Residual lifetime diagnostics of wheelset elements and rail

Estimation of reliability and safe operation of mechanical elements of rail transport is an important and challenging scientific and engineering problem. In order to prevent possible failure of such objects, there is a necessity of reliable prediction of their residual life. Consequently, the aim of the dissertation is to present theoretical and experimental models for calculating the period of fatigue cracks initiation and growth kinetics in the mechanical elements of rail transport and to develop residual life estimation technique for the wheelset elements and rail based on the energy approach of fracture mechanics. Basing on calculation model of a sharp-tip defect initiation in a vicinity of a smooth concentrator of mechanical stress, which is formulated in the dissertation, for the first time, the calculation of the period of fatigue crack initiation at the top of the microdefect on the wheelset axle is performed. New calculation methods for the residual lifetime estimation of wheelsets with surface cracks on the axle are developed by making use of the computational model for the mixed-mode (I+II+III) fatigue crack propagation. The formulated models allow for taking into account the additional influence of the materials fracture macromechanisms of transverse and longitudinal shear on the kinetics of transverse fatigue crack growth on the surface of wheelset axle during its operation. The calculations have shown that the mechanical stresses caused by the weight of the loaded rail car in the transversal section of the wheelset axle journal can significantly accelerate the growth of the transverse fatigue crack on its surface reducing the axle residual life up to about 20%. Therefore, when calculating the wheelset axle residual life with a crack on the surface of its journal, it is necessary to take into account the transverse shear mechanism effect on the kinetics of fatigue crack growth. The dissertation presents a new mathematical model for the fatigue transverse macrocrack growth in a rail basing on the energy approach of fracture mechanics. The rail is simulated by an elastic-plastic beam laying on an elastic basis, that makes it possible to determine the stress state in the material of the rail under operational loads with a sufficient approximation to the real one. On the basis of this model, the calculations of the subcritical growth periods of typical transverse crack-like defects under the rail operation mode are performed. The suggested calculation model can be used as a basis for the development of methods of estimating the frequency of defectoscopy control of rails with defects such as ‘transverse crack’. Based on the finite element method, calculations of the distribution of elastic-plastic deformations in the vicinity of geometric concentrators of mechanical stresses in a tire material during its installation on the wheel centre of the electric locomotive are performed. The calculations show that the local concentrations of mechanical stresses (their maximum values) and the zones of plastic deformation arise on the outer surface of the wheel tire clamp, where, in practice, the fatigue cracks most often occur. The obtained results make it possible to identify the most possible zones of the initiation of fatigue failure in the volume of the tire material prior to its exploitation. The results of the conducted research were used to technical diagnostics implementation of the locomotive mechanical units at the Lviv Locomotive Repair Plant PJSC.