Wear of Polymers

Abrasive wear of polymers has two components material can be removed by the rasping action of a countersurface or it can be sheared off viscoelastically by a countersurface to which it adheres. The precise balance of mechanisms depends on the characteristics of the counterface and the conditions under which the abrasion takes place. Many polymers exhibit excellent wear resistance, which in combination with their low coefficients of friction suit them for applications where lubrication is either impossible or undesirable. We use wear resistant polymers in such diverse applications as bushings in business machines, pump seals, and replacement hip and knee joints. 

G. M. Bartenev, Friction and Wear of Polymers, Elsevier, New York (1981). 

Briscoe, B. J. and Evans, P. D. (1987). The Wear of Polymers by Particle Flows. In Tribology in Particulate Technology. Ed. Briscoe and Adams. Philadelphia Adam Hilger. 

Exposure to the environment (gases and humidity) affects mechanical properties, friction, and wear of polymers. Most of the time, synergistic effects between abrasion, wear and corrosion are created and that amplifies the damage.74,75 Dunn76 has summarized the dominant and synergistic influence of every factor as follows. 

Since several different wear characteristics were noted for the materials tested (e.g.y charring, flow, and brittle behavior), it can be inferred that there is no unique mechanism associated with impact wear of polymer thin films. Further, because of this aspect and the probability that the same mechanisms do not occur under impact testing conditions (Charpy and Izod), it is reasonable to infer that there is little correlation between impact wear resistance and impact strength. This latter point may be illustrated by considering polycarbonate. Even though it has the highest impact strength of any unfilled polymer (4), it exhibits the poorest wear behavior in this study. 

Barteney, G.M. Lavrentev, V.V., "Friction and Wear of Polymers," Lee, L.H. Ludema, K.C., Editors, Translated from Russian into English by D.B. Payne, Elseier, Amsterdam (1981). 

The wear of polymers Is general believed to be caused by one or more of the following mechanisms adhesive transfer, abrasive cutting,... 

In the model most commonly used for fatigue wear of polymers, the wear rate Is assumed proportional to the volume of a wear particle divided by the number of stress cycles N necessary to produce the wear particle. The number of cycles N Is given by... 

In this paper, we have summarized various approaches to controlling the wear of polymers. Several methods appear to be promising 1. structural design, 2. surface modifications, 3 particulate or fibrous reinforcement and 4. interpenetration networks. 

Wear of Polymer Pins Sliding Against Steel Disk. Figures IT (a) and (b) show the variations of fspecific wear rates obtained in the steady states of wear for various polymers with disk temperature. 

Lancaster, J.K., "Abrasion and Wear of Polymers" in "Encyclopedia of Polymer Science and Engineering", Vol. I, John Wiley Sons, 1985. 

Most total replacement joints consist of a metallic and a polymeric component, although alternative materials such as ceramics and carbon reinforced materials are currently being examined for this role. The life of a prosthesis is thus directly affected by the rate of penetration of the metallic component into the polymeric component and this has prompted considerable Interest in the subject of wear of polymers in the hostile environment of the body. 

The objective of this paper is to review the wear of polymers using the above tools in order to characterize the wear process. 

Polymer to Counterface Bonding. Of extreme interest to the tribolo-gist is the nature and structure of interfacial adhesion of polymers to substrate surfaces because it contributes heavily to the adhesive wear of polymers. A very useful tool for the study of this subject is quantitative absorption - reflection thickness infrared spectroscopy (QUARTIR). This device is uniquely suited for the study of preferential orientation of large molecules at interfaces. Thus, insight into the structural interfacial bonding of molecules can be had, adhesion and accordingly adhesive wear better understood. 

A host of analytical tools are available to the tribologist for the study of the wear of polymers and polymer films. Much can be learned about the wear behavior of polymer with visual observation of the wear surfaces with the scanning electron microscope while surface profilometer can assist in quantifying polymer wear. 

A common simulation technique which is used to evaluate the wear of polymers is to slide the polymer, usually in the form of a pin, over the surface of a rotating disc. The pin may be loaded along its major axis, either in a direction normal to or parallel with the axis of rotation. Hence the contact area is produced on the edge or the face of the disc. 

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