Physics of friction

Berman, A. D., Ducker, W. A., and IsraelachivUi, J. N., "Experimental and Theoretical Investigations of Stick-Slip Friction Mechnisms," Physics of Friction, B. N. J. Persson and E. Tosatti, Eds., Kluwer Academic Publishers, 1996, pp. 51-67. 

Friction and lubrication are phenomena which play a crucial role in various aspects of our daily life (I). Despite its importance the physics of friction is only partly... 

Attribute Impact on Syringe Application Physics of Friction Involved... 

Stick-slip motion observed with syringes is associated with the nuxed and boundary lubrication regime. This is in agreement with current models of the occurrence of stick-slip motion for lubricated sliding systems (see Physics of Friction section). Possible causes for this phenomenon are discussed in more detail in the following. 

Persson B N J and Tosatti E (eds) Physics of Sliding Friction (NATO ASI Series E311) (Dordreeht Kiuwer)... 

Mech nic lProperties. Extensive Hsts of the physical properties of FEP copolymers are given in References 58—63. Mechanical properties are shown in Table 3. Most of the important properties of FEP are similar to those of PTFE the main difference is the lower continuous service temperature of 204°C of FEP compared to that of 260°C of PTFE. The flexibiUty at low temperatures and the low coefficients of friction and stabiUty at high temperatures are relatively independent of fabrication conditions. Unlike PTFE, FEP resins do not exhibit a marked change in volume at room temperature, because they do not have a first-order transition at 19°C. They ate usehil above —267°C and are highly flexible above —79°C (64). 

Diverse appHcations for the fabric sometimes demand specialized tests such as for moisture vapor, Hquid transport barrier to fluids, coefficient of friction, seam strength, resistance to sunlight, oxidation and burning, and/or comparative aesthetic properties. Most properties can be deterrnined using standardized test procedures which have been pubHshed as nonwoven standards by INDA (9). A comparison of typical physical properties for selected spunbonded products is shown in Table 2. 

Wear is an economic consideration. Wear resistance generally, but not always, is inversely related to friction level and other desirable performance charactenstics within any class of friction matenal. The objective is to provide the highest level of wear resistance in the normal use temperature range, a controlled moderate increase at elevated temperatures, and a return to the original lower wear rate when temperatures again return to normal. Contrary to common behef, maximum wear life does not require maximum physical and mechanical properties. 

FIGURE 26.6 Friction master curve of an acrylate-butadiene rubber (ABR) gum compound on an Alumina 180 wet surface, (a) wetted with distilled water and (b) 5% detergent added to the water. (From Grosch, K.A., The Physics of Tire Traction, Theory and Experiment, Hayes, D.L. and Browne, A.L. (eds.). Plenum Press, New York/London, 1974.)... 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

Fluorine-containing polymers exhibit unique chemical and physical properties and high performance that are not observed with other organic polymers. They possess high thermal stability, high chemical stability, a low coefficient of friction, low adhesion, water and oil repellency, low refractive index, and outstanding electric insulation. In addition, there have recently been new expectations of selective permeability, piezoelectricity, and biocompatibility. 

Hyun et al. [21] evaluated both the original model by Darnell and Mol [14] and the model by Campbell and Dontula [19] for accuracy against experimental data, and determined that the Darnell-Mol model was less accurate than that of the Campbell-Dontula model. The incorporation of the lateral stress ratio in the calculations supported their conclusions even more. At the time of the work by Hyun et al, however, the physics for screw rotation was not well appreciated, and the evaluations for the Campbell models [23] were performed with coefficient of friction... 

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