Friction mechanisms, basic

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. 

Knowlton has cautioned on the difference between small diameter and large diameter systems for pressure losses. The difference between these systems is especially apparent for dense phase flow where recirculation occurs and wall friction differs considerably. Li and Kwauk (1989, 1989) have also studied the dense phase vertical transport in their analysis and approach to recirculating fluid beds. Li and Kwauk s analysis included the dynamics of a vertical pneumatic moving bed upward transport using the basic solid mechanics formulation. Some noncircular geometries were treated including experimental verification. The flows have been characterized into packed and transition flows. Accurate prediction of the discharge rates from these systems has been obtained. 

In particulate-filled thermoplastics, the matrix is the load-bearing component and all deformation processes take place in the matrix. Particulate fillers are, in most cases, not capable of carrying any substantial portion of the load due to the absence of interfacial friction as the means of stress transfer. This is evidenced by the lack of broken particles on the surfaces of fractured filled thermoplastics. Hence, it seems appropriate to start this volume with a brief overview of the basic structural levels and manifestation of these levels in governing the mechanical properties of semicrystaUine thermoplastics used in compounding. 

The crucial point is to simulate the previously identified basic stress modes impact and friction under well defined stress conditions. This way, material properties can be related to attrition caused by these stress modes and the respective attrition mechanisms in effect. For this purpose it was chosen to perform single particle experiments in simple experimental setups to realize the defined stress conditions. Details on these setups are given in the next section. 

This is generally obtained by use of the integrated form of the mechanical energy equation with the frictional energy loss calculated by Eq. (65). Thus, the basic problem facing a design engineer is how to obtain numerical values for the friction factor /. 

Because the basic fuel cell needs no mechanical drive, its operation is quiet and involves no frictional losses (Figure 2.100). These characteristics should make it possible to locate them near the final user, producing a more even distribution of the generation capacity. Auxiliaries, particularly fans and blowers, must be quiet therefore, they should be well supported to prevent their motion and be provided with variable-speed drives. In addition, the feathering of the blade edges and the use of noise-reducing enclosures are recommended. 

So far, we have considered the elasticity of filler networks in elastomers and its reinforcing action at small strain amplitudes, where no fracture of filler-filler bonds appears. With increasing strain, a successive breakdown of the filler network takes place and the elastic modulus decreases rapidly if a critical strain amplitude is exceeded (Fig. 42). For a theoretical description of this behavior, the ultimate properties and fracture mechanics of CCA-filler clusters in elastomers have to be evaluated. This will be a basic tool for a quantitative understanding of stress softening phenomena and the role of fillers in internal friction of reinforced rubbers. 

As described in the last section, the adhesion forces between the particles and the polished surface can provide insight into post-CMP cleaning mechanism and efficiency. As a matter of fact, measurements of adhesion force and alike can directly help in the understanding of CMP and post-CMP cleaning processes. In this section, some basic principles and applications of adhesion and friction force measurements in copper CMP will be presented. The discussion is certainly applicable to post-CMP cleaning processes when similar systems are involved. 

This model is based on quasimolecular dynamics, in which the medium is assumed to be composed of an assembly of meso-scale discrete particles (i.e., finite elements). Tlie movement and deformation of the material system and its evolution are described by the aggregate movements of these elements. Two types of basic characteristics, geometrical and physical, are considered. In tlie geometrical aspect, sliapes and sizes of elements and tlie manner of their initial aggregation and arrangement are the important factors. In the physical aspect, mechanical, physical, and chemical characteristics, such as the interaction potential, phase transition, and chemical reactivity may be tlie important ones. To construct this model, many physical factors, including interaction potential, friction of particles, shear resistance force, energy dissipation and temperature increase, stress and strain at the meso- and macro-levels, phase transition, and chemical reaction are considered. In fact, simulation of chemical reactions is one of the most difficult tasks, but it is the most important aspect in shock-wave chemistiy. 

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