CONTACT MECHANICS AND FRICTION: PHYSICAL PRINCIPLES AND APPLICATIONS

Everybody who deals with the problem of the contact mechanics between wheel and rail sooner or later has to deal with two books. One of these books is Johnson’s book on contact mechanics (K. L. Johnson: Contact Mechanics, Cambridge University Press, 1985; 6. Edition 2001) and the other is Kalker’s monograph (J. J. Kalker: Three Dimensional Elastic Bodies in Rolling Contact, Kluwer Academic Publishers, Dordrecht, 1990). Both books go beyond the rolling contact mechanics of wheel-on-rail contact. With Kalker, the problem revolves around numerical treatment of contact problems for elastic bodies. Everybody who wants to deal with contact mechanical problems for real wheel-rail systems, including wear, cannot ignore the work of Kalker. In Johnson’s book a broad variety of contact mechanical problems are considered, not only in the field of theory of elasticity. Johnson always uses analytical, semi-analytical, or graphical solutions. Now, as announced in the title, there is an additional book in this field at Springer publishing house, initially for the German-speaking world and now as an English edition. One naturally asks, if another book in this field is justified, given that two monographs on the subject already exist. The answer is definitely: Yes. The reason for this answer becomes clear from the title: Contact Mechanics and Friction go hand in hand. The subtitle makes it clear that the book is not limited to a purely mechanical problem, but rather it reaches back to physical fundamentals. The reviewer agrees with the author of this book in that (even with apparently ‘‘pure’’ technical problems such as the wheel-rail contact) it is impossible to avoid physical considerations, if one is required to tackle previously unsolved or unsatisfactorily solved aspects. The book by Popov allows new problems to be considered more easily than before. Popov primarily writes not for academic colleagues, but for students and engineers in the field of contact mechanics. Valentin Popov believes that the essential aspects of contact mechanics and friction are much simpler than they often appear to be. The author has succeeded in presenting very complicated situations in the simplest possible way. Thereby, he exposes himself to criticism from colleagues in the field of physics for oversimplifying matters. Obviously, he does not stop short of this criticism, for he first wants to help the beginner to overcome his psychological inhibitions. Already by perusing the table of contents, a broader aspect becomes clear. Chapters 2 and 3 deal with a qualitative approach whereas Chapters 5 and 6 with a ‘‘rigorous’’ approach. Above all, it is essential to the author to gain fundamental insights with a qualitative approach; only then does the author draw near to a more stringent procedure for the exact solution. However, even there he still limits himself (for instance with Hertzian contact problems) to the simplest case (sphere on a half-space) for the generalized cases, once again he provides an approximation. It is important to the author to convey basic insights into general problems: adhesive contact, roughness, frictionally induced oscillations, thermal effects, viscoelastic properties, wear, and influence of high frequency vibrations. Compared with the German edition one can find an additional chapter entitled ‘‘Earthquake and Friction’’. Of course, this chapter is not necessary for rolling contact problems; however it indicates how the author tackles completely new problems. The focal point, above all regarding the wheel-rail contact, is composed of the rolling contact problem and Coulomb’s law of friction. At this the PrandtlTomlinson model of dry friction is considered in detail. In Chapter 19 of Popov’s book, numerical simulation methods for contact mechanics and friction are covered. Of main interest is a procedure in which a three-dimensional contact problem is consistently represented as a one-dimensional problem. A certain proximity to Kalker’s simplified theory is unmistakable. Popov, however, goes further when he applies his simulation method, which he calls reduction method, to the contact of rough surfaces. Different from Kalker (FASTSIM), the transition to arbitrary contact surfaces is (still) not possible. The reader of this book should not expect a universal remedy. The fact that understanding is linked to some amount of effort will become very clear, at least, 341