Mechanical properties tribological effects

Unlike traditional textbooks of tribology, in this book we regard boundary lubrication as a limit state of hydrodynamic lubrication when film thickness is down to molecular dimension and independent of the velocity of relative motion. The discussions are based on the existing results, some from literatures but mostly from the authors own work. The topics are mainly focused on the mechanical properties of boundary films, including rheology transitions, molecular ordering, and shear responses. Ordered molecule films, such as L-B films and SAM, are discussed, with emphasis on the frictional performance, energy dissipation and the effects from structural features. Boundary films can be modeled either as a confined substance, or an adsorbed/reacted layer on the... 

The surface characteristics of materials dominate the performance of the final products in many applications. For instance the mechanical behavior of composite materials are strongly dependent on the nature of the fiber/matrix interface, the lubricant properties are influenced by surface tribological effects, the success of bio-implants is mostly determined by biocompatibility, etc. 

Nishitani, Y. Yamada, Y. Sekiguchi, I. Ishii, C. Kitano, T. (2010). Effects of Addition of Functionalized SEBS on Rheological, Mechanical, and Tribological Properties of Polyamide 6 Nanocomposites. Polymer Engineering and Science, Vol.50, No.l, pp. 100-112 ISSN 0032-3888... 

This combination of materials has had a profound effect upon the development of surgery for the treatment of Joint disease and prostheses are readily available, not just for the hip joint but also for the knee, ankle, shoulder and other joints. It is the good biological acceptability of UHMWPE coupled with its mechanical properties that has led to this widespread acceptance. In particular, the tribological characteristics appear to be the most satisfactory for use in a metal-polymer combination. Prosthesis designs utilising alumina ceramic also incorporate an acetabular component of UHMWPE in consequence of the low rate of wear observed. 

S. Kim, N. Saka, J.-H. Chun, Pad scratching in chemical-mechanical polishing the effects of mechanical and tribological properties, ECS J. Solid Sate Sci. Technol. 3 (5) (2014) 169-178. 

With these complications in mind, research in this area has blossomed rapidly. Two main foci of research in this area are on (1) how external conditions (such as levels of loadings, the use of different indenters, and scratch rate) and (2) intrinsic materials properties (such as modulus and crystallinity) affect the tribological behaviors of the polymers. Apart from examining the scratch resistance of polymers, a closely related quantity which is of interest would be changes in coefficient of friction. Studies relating mechanical properties (3-5,9,36,71,75,76), deformation patterns (18,33,63,71,77-81), fabrication process (3,5,35,72,77,82-86) with respect to experimental parameters, snch as temperature (18), loading effect (24,71,72,87-96), indenter geometry (21,33,75,82,95,97), and scratch velocity (21,56,57,59,64,65,96,98) have been carried ont. In addition, scratch maps for different polymers have been produced (32,33), and various scratch resistance properties estimated (33,37,56,58,59,99). 

Hofste JM, Schut JA, Pennings AJ. The effect of chromic acid treatment on the mechanical and tribological properties of aramid fibre reinforced ultra-high molecular weight polyethylene composite. J Mater Sci 1998 October 9(10) 561-6. 

The two most often used fillers in thermoplastics are PTFE and PDMS or silicone. The respective functions of the two materials are quite different. PTFE is almost the wonder additive for tribological applications, whether in a solid polymer or liquid lubricant. The mechaiucal properties of PTFE hold over a range of -260°C to 260°C with a melt temperature of 321°C. It is chanicaUy inert and hydrophobic. The effect of PTFE as a solid lubricant can be understood from its performance as a homopolymer. As a homopolymer, PTFE has the lowest coefficient of friction of all polymeric materials sliding against metal surfaces. This is due to the lack of bulky side groups on the molecular chain and the formation of a low friction transfer film on the opposing counterface. However, due to the poor mechanical properties, PTFE alone also... 

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