Frictional deformation

PROCESSES The two surfaces may contact each other. Elastic and plastic deformation. Frictional heat. Wear. EXOEMISSION Triboemission (radicals, electrons, photons, positive ions, X-ray emission). After-emission electrons. STRUCTURE Upper layer long chain polyphosphates. Lower layer short chain polyphosphates. 

Where one or both of the contacting surfaces becomes permanently deformed during sliding, the energy required to produce the deformation represents an additional component of the friction force. For engineering surfaces the amount of permanent deformation which can be tolerated is very limited so that the deformation friction is small in comparison with the adhesive friction. Elastic deformation only makes a significant contribution to the total friction when there is a high level of hysteresis in the elastic recovery, such as in vehicle tyres, and this is not normally a consideration when molybdenum disulphide is used. For practical purposes it can therefore be assumed that adhesive friction is the only type of friction which needs to be considered. 

Czichos, H. Feinle, P. "Tribological Behaviour of Thermoplastic, Filled, and Glass-Fibre- Reinforced Polymers - Contact Deformation, Friction and Wear, Surface Investigations", BAM Research Report 83,... 

Another important classification that will be referred to routinely is single fiber and fiber assembly properties. The more important single fiber properties are elastic deformations, friction, cross-sectional area (diameter), static charge, luster or hair shine, and cohesive forces. 

Measurements Normal load, cartilage deformation, friction cartilage wear and damage, biochemical analysis of cartilage specimens, synovial fluid, and wear debris sub-surface changes... 

Cutting force Interatomic forces F = tF i = E- jsei yV/ Plastic deformation/ friction... 

Adhesion and Deformation Friction of Polymer on Hard Solids... 

The main objective of this paper is to present a detailed view of various aspects of adhesion and deformation friction based mainly upon the research findings of this laboratory. An attempt is also made to analyse the large number of results reported elsewhere in order to develop a coherent presentation. Certain fundamental aspects of friction are discussed at first from a phenomenological point of view. A discussion of the law of friction relating to motion follows with a study of the stick-slip phenomena. The next part deals with the isothermal adhesive friction of elastomers on nominally flat and smooth surfaces. 

PRELIMINARY CONSIDERATIONS SURFACE PROPERTIES RELATED TO FRICTION QUALITATIVE DESCRIPTION OF THE MECHANISM FUNDAMENTAL ASPECTS FACTORS AFFECTING FRICTION RELATIVE MOTION AND TEMPERATURE DISPLACEMENT DEPENDENCE IN INITIAL FRICTION NORMAL LOAD, NOMINAL AREA, PRESSURE AND SURFACE ROUGHNESS MATERIALS FOR FRICTION PAIR Elastomer Properties Counterfaces of Hard Solids EVALUATION OF THEORETICAL MODELS A QUASI-QUANTITATIVE THEORY Friction of Asperities Details of Calculations Other Factors DEFORMATION FRICTION CONCLUSIONS... 

The term deformation friction" or "hysteresis component" is usually used to denote a secondary energy dissipation mechanism... 

The basic physical picture may be described as follows. During the motion, various points within a body experience different loading histories. For inelastic materials with memory, the deformation response of the material depends upon the loading history. This leads to asymmetric distributions of normal pressure and deformation even if the initial geometry of the static problem is symmetric with respect to an axis normal to the direction of motion. The asymmetry gives rise to a resistance to the motion. The resistance is known as the deformation friction. 

Another way of looking at the problem is to consider that the energy fed into the material, ahead of the contact area is not fully recovered behind the contact area energy is dissipated on account of the inelasticity of the material. The energy loss may be considered to be the cause of the deformation friction. 

It is possible to conceive that the mechanism occurs at two scales of deformation. In the case of concentrated contacts, the mechanism may arise mainly from bulk deformation of bodies. On the other hand, the asperities on extended surfaces may also give rise to such a mechanism during their relative motion. The terms such as ploughing and grooving (non-permanent) of polymers may be thought to describe the latter. The importance of this kind of deformation friction is not yet established rigorously. It is not easy to carry out experiments in which adhesion is totally absent, with a view to obtain the contribution resulting from deformation friction. Neither is any analysis of the problem available currently. The viscoelastic stress analysis involves time dependent, mixed boundary conditions. 

From the explanation concerning the origin of deformation friction, it is not surprising that the frictional resistance is closely related to the viscoelastic properties. It has been established that the coefficient of rolling friction exhibits a maximum at a certain speed of translation. It may also be expected that temperature has a profound effect on the coefficient of rolling friction. The speed-temperature equivalence may again be expected. 

The various simpler theories of deformation friction have been presented by Moore ... 

They base their definition of deformation friction upon the differential work done in moving a pressure profile over an infinitesimal distance. Yandell has described an interesting mathematical model for the viscoelastic bodies. He uses framework of elastic and frictional elements in his analysis. It would be interesting to evaluate the various approaches, to the purpose of consolidating our understanding of deformation friction. 

Some efforts have been made to study the deformation friction which occurs during sliding over well lubricated surfaces. Tabor found that the coefficient of rolling and sliding friction were almost equal. A friction coefficient of the order of 0.1 was found to be representative of both the modes of motion at very low speeds. 

The major ideas pertaining to deformation friction have been described. The deformation friction occurs on two different scales. The significance of these results has been discussed. 

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