Friction systems, wear mechanisms

Beside mechanical characterization, one important aim of this work is the evaluation of the effects of E-beam modification of PTFE powder on the friction and wear properties of PTFE-filled EPDM composites crosslinked by a radical-initiated peroxide system. Friction and wear properties of EPDM composites were... 

The state of the art in friction and wear of PTFE-filled rubbers include the effects of many important system parameters, such as the composition of the rubber formulation, particle dispersion, bulk mechanical properties, ability of transfer film formation, and the chemistry between PTFE powder and the rubber matrix. Although the present study has explicitly highlighted the potential of PTFE powder in rubber matrixes with significant property improvements in the friction, wear, and physical properties, it has simultaneously opened a new field regarding the use of PTFE powder in rubber compounds, with some challenging tasks for chemists, engineers, and material scientists. 

Because of the continuously changing nature of the friction process, many different mechanisms of friction and wear may operate simultaneously with one or two mechanisms dominating. The dominant mechanism is different from one friction system to another. In addition, for a given friction system, the dominant... 

More detailed study indicates that transfer wear actually exists during CMP.52 The interactions between a copper wafer and urethane polishing pads were characterized to investigate the effects of friction on removal mechanisms of a polishing system of copper interconnected wafers in water. In situ... 

Mechanical joints for assembling microfluidic components and systems often involve insertion of one part into another. The aforementioned cartridges are a simple example, and structures must be included on both the cartridge and inside the instrument to allow smooth insertion. Such structures can include micro-rails to aid such sUding assembly on-chip. Care must be taken in choosing materials for properties such as friction and wear. Friction is deflned as the force of motion or tendency toward such of two surfaces in contact, defined by the equation ... 

It is clear from the literature classification of friction (usually classified as a branch of Physics or of Mechanical Engineering) and wear (for metallic systems often considered to be part of Metallurgy) that an ACS Symposium on polymer friction and wear encompasses an enormous range of traditional disciplines. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Based on the discussion in earlier sections of this chapter, one may expect atomically flat incommensurate surfaces to be superlubric. Indeed the first suggestion that ultra-low friction may be possible was based on simulations of copper surfaces.6,7 Furthermore, the simulations of Ni(100)/(100) interfaces discussed in the previous section showed very low friction when the surfaces were atomically flat and misoriented (see the data for the atomically flat system between 30° and 60° in Figure 21). In general, however, it is reasonable to assume that bare metals are not good candidates for superlubric materials because they are vulnerable to a variety of energy dissipation mechanisms such as dislocation formation, plastic deformation, and wear. 

The work function of the rubbing surfaces and the electron affinity of additives are interconnected on the molecular level. This mechanism has been discussed in terms of tribopolymerization models as a general approach to boundary lubrication (Kajdas 1994, 2001). To evaluate the validity of the anion-radical mechanism, two metal systems were investigated, a hard steel ball on a softer steel plate and a hard ball on an aluminum plate. Both metal plates emit electrons under friction, but aluminum produced more exoelectrons than steel. With aluminum, the addition of 1% styrene to the hexadecane lubricating fluid reduced the wear volume of the plate by over 65%. This effect considerably predominates that of steel on steel. Friction initiates polymerization of styrene, and this polymer formation was proven. It was also found that lauryl methacrylate, diallyl phthalate, and vinyl acetate reduced wear in an aluminum pin-on-disc test by 60-80% (Kajdas 1994). 

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