MIDIT OFD CATS Modelling, Nonlinear Dynamics Optics and Fluid Dynamics Chaos and Turbulence Studies and Irreversible Thermodynamics Risø National Laboratory Niels Bohr Institute and Technical University of Denmark Building 128 Department of Chemistry Building 321 P.O. Box 49 University of Copenhagen DK-2800 Lyngby DK-4000 Roskilde DK-2100 Copenhagen Ø Denmark Denmark Denmark
by Jerzy Piotrowski
Faculty of Automobiles and Heavy Machines Engineering
Warsaw University of Technology
Warsaw, Poland
MIDIT-seminar 422
Thursday November 5, 1998, 14.00 h
at MIDIT, IMM Building 305, room 027
Abstract: A fast, approximate method to calculate contact between wheel
and rail will be presented. The normal contact is calculated in one step. To
calculate creep forces the FASTSIM algorithm has been implemented to non-elliptical
contact region obtained by normal contact calculation. Results are compared with
solutions obtained with the program CONTACT by Kalker. The performance of the
method, according to numerous comparisons with the program CONTACT, is very
good as far as the normal contact is concerned. Creep forces calculated with
the approximate method + FASTSIM are reasonable when compared with solutions
from the program CONTACT.
In many practical cases the contact area between wheel and rail is curved as it
is spread over a curved section of profiles. For weakly curved contact area
the methods of contact mechanics employing the half-space assumption for
elasticity are used which neglect contact area curvature. Even for moderately
curved contact area these methods are employed to obtain some approximation
to the exact solution - which is presently not available.
It is proposed to calculate normal problem for weakly curved contact with the
forementioned method but to take into account curvature of the area while
calculating creep forces during rolling. To this end so-called non-dimensional
rigid slip should be calculated directly for each point of the contact area
using the profile data.
A derivation of the rigid slip is given which does not use the notion of the
spin creepage, which is a global quantity related to so-called point of
geometrical contact.
The influence of contanct curvature on creep force is presented on three
examples. The first example is a steel roller rolling in the groove. The
next two examples refer to railway wheel/rail. The creep forces for the last
two examples have been compared with those calculated in a usual manner when
one neglects the curvature of the contact area. The differences in creep
forces for considered two approaches can be significant, which may be
important for modelling rail vehicle-track interaction.
A demonstration computer program will be presented which allows submitting
any (including drawn by hand) profile and separation data. The solution is
presented graphically and shows the contact area and the distribution of
tangential stresses. This program demonstrates reliability and speed of the
approximate method for calculating normal contact and creep forces.