Polymer wear mechanisms

There are many other examples of chemical reactions being induced by shearing stresses. A mechanism involving metallization seems plausible. Areas of application include photochemistry, degradation of polymers, friction and wear, mechanical alloying and cutting processes. 

Thus, in the spring of 1984, an international symposium with the theme Polymer Wear and Its Control was held, and is the basis of this book. The purpose of the symposium was to seek better understanding about wear mechanisms of polymers and to develop new wear-resistant materials. Distinguished scientists and engineers were invited from West Germany, England, Japan, and the U.S.S.R. to present plenary lectures. Thirty-one papers were presented. The conference was very much appreciated by those who attended. 

We are pleased to present, in this volume, 26 reviewed and revised chapters from the symposium in six parts mechanisms of polymer wear controls of polymer wear tribological behaviors of polymers wear of biomaterials and polymer composites characterization and measurements of polymer wear and degradation and wear of polymeric films and filaments. 

Czichos, H. "Influence of Adhesive and Abrasive Mechanisms on the Tribological Behaviour of Thermoplastic Polymers", Wear 88 (1983) 27. 

Polymer wear can take place in various modes, e.g., adhesive, abrasive, transfer, fatigue, and tribo-chemical. In reality, several mechanisms can also operate simultaneously. If impaction is involved, an impact wear can be the chief mechanism. The predominance of any one type of wear can be influenced by the form of polymers, e.g., thermoplastics, elastomers or composites. 

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. 

Several mechanisms of polymer wear have been discussed in the literature (5-7) adhesive wear, abrasive wear, fatigue wear, tribo-chemical wear, corrosive wear and impact wear. We shall limit this discussion to the four basic mechanisms shown in Figure 1. Neither corrosive(5) nor impact wear(8,9) are common, and we do not plan to discuss these in this paper. 

Tribo-chemical Wear. Besides the above three wear mechanisms, we should discuss tribo-chemical wear. Tribo-chemical wear(7) takes many forms. Some of these wears result from the interactions of the polymer with its environment, e.g., oxygen, ozone, heat (e.g., friction heat), surface contaminants, etc.- The application of mechanical energy at the interface can also cause mechanochemical degradation(35) to generate free radicals which can further lead to cross-linking or other interactions. In the composites, polymer-filler interactions can also take place through mechanochemical mechanisms. 

When polymers slide on machined metal surfaces, it is quite possible that steady-state wear Involves a combination of abrasive, fatigue, and adhesive wear mechanisms. To study fatigue wear, it would be desirable to minimize the contributions of the abrasive and adhesive wear modes. In this paper, the following polymers polycarbonate, polyvinyl chloride, ultra-high molecular weight polyethylene, siloxane modified epoxies, and polylmldes are tested in experiments in which the fatigue wear mode is predominant. 

The experiment chosen to emphasize the fatigue wear mechanism was a 52100 steel ball 3.18 mm dia. loaded against a rotating polymer disk ( ). The load was adjusted so that stresses in the polymer were not high enough to cause wear and the formation of a wear track when... 

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. 

Thus, the new method for studying the molecular characteristics of the thermoplastic polymer transfer and wear products makes it possible to establish the orientation of mechano-chemical processes in the rubbing zone and to find ways of dispersion and wear control. The method also enables the wear mechanisms of antifriction polymers to be studied in terms of the transfer phenomena. 

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... 

Figure 7 indicates the amount of polymer transfer on wear that occurs as a function of a mechanical parameter, sliding speed. An examination of Figure 7 indicates that the higher the sliding speed for a polymer in contact with a metal the greater the film thickness and accordingly the amount of polymer wear. 

Various tests and analytical methods are used for the characterisation and evaluation of the properties of vegetable oil-based polymer composites. Mechanical tests for properties such as tensile, flexural, compressive, impact, hardness and wear are carried out by a universal testing machine (UTM), and by equipment for testing impact, hardness, abrasion loss, and so on. Weather and chemical resistance tests are performed in UV/ozone, an artificial environmental chamber and in different chemical media. Water uptake and biodegradability tests are carried out by standard ASTM methods. Biodegradability and biocompatibility may be studied by the same procedure as described in Chapter 2. However, in practice only a few such studies have been performed for vegetable oil-based composites. 

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