Introductory Remarks

Abstract

Mr. Hays and Dr. Browne, ladies and gentlemen, it is a distinct pleasure to be here today. For my part, I would like to express my congratulations to the participants of yesterday’s sessions for the most informative and entertaining meetings, and I can only hope that our efforts today will measure up to the standards they set. I stand before you in a little bit of awe. In thinking over my introductions to the speakers for this session, and in thinking over these brief remarks, it struck me just how much we cannot yet do analytically in the field of mechanics as applied to tires. The goal of mechanics in tire technology is, given a handbook of material properties, a mold design drawing, and post-cure inflation and drum set specifications, to be able to calculate all the performance characteristics of the tire, including its wear rate and tractive characteristics on a given surface. Needless to say, we have a little way to go to achieve that goal. Nevertheless, the material properties of the constituents can be measured readily. We have available rather elegant shell theories, constructed, it is true, primarily for shells of fixed geometry, but nevertheless, elegant. We understand the mechanics of orthotropic or anisotropic elastic bodies. Yet truly adequate means of calculation for the simplest tire properties still elude us, and we must fall back on rather crude models involving strings, beams, and springs. But part of the trouble lies in the fact that contained in the problem of analytical representation of a tire are many difficulties which have been dealt with separately in mechanics but almost never altogether. Some of these are: highly anisotropic, cord-reinforced materials; non-linear elasticity in some components; appreciable hysteresis effects; large deformations of shells; frictional forces not describable by simple frictional laws; and permanent set and heat contraction of materials. For the moment we must content ourselves with small pieces of the overall problem. We wait expectantly for attempts to adopt finite element techniques to the calculation of tire deformations, yet even here, we sense limits. These are based on the knowledge that not all of the physics of friction is clearly formulated, so that the interaction of shear forces, normal forces, and tire deformation is still not analytically clear. In spite of all the difficulties and the failures, progress has been and is being made. Today we have many excellent young engineers and scientists engaged in applying mechanics to tire technology. Many of these are in the audience today. We welcome them and we hope that they share with us the excitement of working on a truly difficult problem in mechanics which has great practical application both in terms of safety and economics. Today we are fortunate to have four papers in this session which summarize and in some cases, condense some of the properties of the tire itself as it pertains to traction and point out some explanations for observed phenomena.