Energetics, polymer wear

Fracture Energetics and Surface Energetics of Polymer Wear... 

Since the first review on the effect of surface energetics on polymer friction and wear published in 197, (0 many new works have appeared. Some of these papers(2- ) are on fracture mechanics. In this paper we shall review our current knowledge about both fracture energetics and surface energetics of polymer wear. First, we discuss wear mechanisms and then emphasize these two aspects related to each wear mechanism. 

They are capable of providing insight into the presence or absences of transfer (wear), the adhesive strength of polymer to metal, amount of transfer, bond scission, mechanical effects such as loading of surfaces together, chemical effects on bonding and surface energetics. The field ion microscope coupled with the atom probe is the ultimate tool for the study of polymer wear because it allows... 

The basic factors which influence polymer wear > are pressure, coefficient of friction, surface texture, sliding velocity, elastic modulus, strength and fatigue resistance. Surface energetics may affect polymer wear through the adhesional friction. Thus, a direct correlation between surface energetics and polymer wear is not apparent. 

In view of the indirect roles of surface energetics in numerous forms of polymer wear, we can not establish a unique correlation between surface energetics and each of the above discussed mechanisms. The transfer of polymer to the counterface does not follow a certain set of rules or regularities. Pooley and Tabor concluded that the low friction and the light transfer of PTFE and polyethylenes are not affected by surface energy, e.g. or crystal texture of the polymer, or the crystallite size. The transfer is essentially due to smooth molecular profiles. On the other hand, Tanaka observed the formation of a long band on PTFE and determined the wear rate to be a function of the width of the bands rather than the crystallinity. This wear mechanism bears a similarity to that of delamin-ation ... 

Abrasive Wear. Abrasive wear(18) is common for brittle, ductile and elastomeric polymers. Abrasion is the wear by displacement of materials from surfaces in relative motion caused by the presence of hard protruberanees or by the presence of hard particles either between the surfaces or embedded in one of them. As a result, microploughing, microshearing or microcutting can occur. Thus, fracture energetics and contact mechanics are involved in analyzing the wear results. We shall discuss briefly the wear rate with respect to different types of polymers. 

In comparison with metals, most conventional polymers are low in wear resistance. For wear control, we need to understand various wear mechanisms for each polymer system (V). As discussed in a previous paper, for adhesive wear, surface energetics can determine the extent of surface wear. Thus, a low surface energy is preferred to minimize the surface attrition. In addition, a harder polymer is desired to lower the wear rate. For abrasive wear, fracture energetics become important a harder and tougher material should be more wear resistant. 

After Dr. Tabor s paper, I shall survey the effects of surface energetics on polymer friction and wear. I hope that my paper will provide some insight about various interactions at the interface. 

Effect of Surface Energetics on Polymer Friction and Wear... 

Friction and wear involve sol id-to-solid contacts governed by Van der Waals and electrostatic interactions on the surface of a friction pair. Thus, surface energetics could play a major role in determining polymer friction, if deformation of bulk were not accompanying the contact phenomena. This paper discusses both the relevance and irrelevance of surface energetics to polymer fri ction. 

This paper will discuss the relevance and the irrelevance of surface energetics to polymer friction and wear. This survey covers most of the important works published in the past and during this recent Symposium. Since basic principles related to polymer friction have been reviewed by Tabor, and by Savkoor, the scope of this discussion will be limited to pertinent friction mechanisms with emphasis on surface interactions. First will be a brief discussion of the following friction processes polymer sliding, elastomer sliding, lubricated polymer sliding, polymer rolling. 

Giltrow showed that wear rates can be correlated with cohesive energies of polymers. Polymers with high cohesive energies have low wear rates. Cohesive energy which is a measure of intermolecular bond strength can also affect surface energetics of polymers ... 

The hypothesis has been that the adhesion between the rubbing surfaces plays a dominant role in the friction and wear processes of the micropairs investigated. It was necessary therefore to estimate the surface energetics of the real polymer microelements, because the surface free energy of a polymer depends not only on the chemical structure of macromolecules but also on the manufacturing conditions. The miniature polymer bushings were manufactured in a mold at a temperature of 80°C with polished surfaces. 

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