What is Tribology, Anyway?
- PDF / 1,346,460 Bytes
- 3 Pages / 604.8 x 806.4 pts Page_size
- 95 Downloads / 195 Views
in applied research as well as those in more académie activities. The first article, by Steve Granick, addresses some of the exciting activities in the area of "molecular" tribology, i.e., studies, both theoretical and expérimental, which address the interactions of surfaces from an atomic or molecular viewpoint and use terminology such as interatomic forces and distances, but include not only atomically smooth and "clean" surfaces but also deal with the présence of liquid lubricant between the surfaces at thicknesses so small that significant déviations from macroscopic viscosity concepts are clearly évident. The point is made that this is of real practical importance because the interaction of loaded engineering surfaces occurs through the close proximity of "high spots" or asperities in the respective surfaces, and the locally high pressures give rise to very close approach of the surfaces. On the other hand, the strong increase in viscosity and even glass transitions or "crystallizations" can often maintain small but finite séparations of the surfaces. With the scène set for appreciating the atomic nature of surface interactions, the second paper by D. Landheer and ATW de Gee builds on interatomic interactions to illustrate the more macroscopic aspects of adhésion of surfaces, asperity contacts, interfacial slip, and plastic déformation, introducing the picturesque language of plowing (or, if you learned English rather t h a n "Americaneze," ploughing) and "stick-slip" motion between two sliding surfaces. Illustrative of the complexity of even such elementary interactions is the fact that the relative importance of adhésion and plowing in determining the macroscopically observed friction coefficient remains a topic of dispute in current literature. This article should greatly aid in clarifying, if not settling, that debate. The third article, by H.S. Kong and M.F. Ashby, explores the even "messier" aspects of localized sliding interactions, i.e., the dissipation of the heat generated
from the work of overcoming frictional forces. In the spirit of the now-classic treatments by Ashby and co-workers of déformation maps, sintering maps, and fracture maps, thèse authors develop friction-heating maps to predict the températures generated at the interfaces between sliding bodies of differing mechanical and physical properties. Since actual contacts occur typically over régions small in comparison with the nominal contact areas, correspondingly much higher or "hot-spot" températures are obtained in those local régions and a milder but still often considérable gênerai or average "bulk" température between the hot spots. The authors hâve developed a general-purpose computer model that can simulate many différent geometries, pressures, and sliding velocities. As a particularly fascinating application of the model, they discuss the well-known fabrication technique of friction-welding, show good concurrence between model and experiment for several Systems, and also illustrate why people hâve found empirically that PTFE (poly
Data Loading...
