Study of wear of tyre treads

Abstract

Wear of vehicular lyre treads is an important practical issue. Since the service life of a lyre is primarily affected by the wear of treads, a useful study of lyre treads is of great practical importance for the optimum design and thus improved life of lyres. The present' thesis describes a new investigation for the identification of the causes responsible for the lyre wear and a method to provide a useful guideline for reducing the wear of lyre-treads through an extensive analysis of the mixed boundary-value contact problem of lyre-tread. Earlier, no seriouS attempt was made to provide a reasonable guideline for the optimum tread sections that would ensure no wear of the treads. Actually, it has not been successful in the past mainly because of the inabilily of simulating the contact problem through an appropriate mathematical modeling where all the boundary conditions would be satisfied justifiably. . An ideal mathematical model for the practical stress problems, namely, the displacement potential function formulation has been used in conjunction with the finite-difference method of solution for the present analysis. For the present computational investigation all the necessary material properties of lyre are obtained experimentally. For the purpose of wear analysis, first, the contact surface of the lyre tread is assumed to be free from frictional force, and the corresponding solution of the problem is obtained where the contact boundary is only subjected to a uniform normal compressive loading from the road surface. The results of this frictionless analysis however give the basis for realizing the fact that the continuous lateral slipping action of the tread contact surface on the road plays the. most important role in shortening the life of lyres as far as the wear is concerned. Secondly, the solution of the problem is obtained by restnctmg the tangential displacement of the contact boundary, which is subjected to a uniform compressive stress from the road surface. From the resulting distribution of the shearing stress along the contact boundary, a relationship between the maximum shearing stress developed and the aspect ratio of the tread section is established under different contact pressures. Finally, the maximum calculated coefficient of friction obtained from the maximum shearing stress, are analyzed in the perspective of tread aspect ratio, where the dimensions of the tread section are varied in both the normal and lateral directions. From the comparison of the calculated friction coefficient with the friction coefficient available from the road, an optimum value of the aspect ratio is determined, which ensures no wear of tyre tread due to the lateral slipping of the contact surface on the road. In addition to the effects of dimensional parameters, the wear of the contact surface is analyzed for different lyre materials and also for different inflation pressures. Moreover, attempt is made to investigate the distributions of different stress components along the bond line region near the ply, which might be responsible for the separation of the tread from the ply.