Composite polymers wear mechanics

We are pleased to present, in this volume, 26 reviewed and revised chapters from the symposium in six parts mechanisms of polymer wear controls of polymer wear tribological behaviors of polymers wear of biomaterials and polymer composites characterization and measurements of polymer wear and degradation and wear of polymeric films and filaments. 

Polymer wear can take place in various modes, e.g., adhesive, abrasive, transfer, fatigue, and tribo-chemical. In reality, several mechanisms can also operate simultaneously. If impaction is involved, an impact wear can be the chief mechanism. The predominance of any one type of wear can be influenced by the form of polymers, e.g., thermoplastics, elastomers or composites. 

Tribo-chemical Wear. Besides the above three wear mechanisms, we should discuss tribo-chemical wear. Tribo-chemical wear(7) takes many forms. Some of these wears result from the interactions of the polymer with its environment, e.g., oxygen, ozone, heat (e.g., friction heat), surface contaminants, etc.- The application of mechanical energy at the interface can also cause mechanochemical degradation(35) to generate free radicals which can further lead to cross-linking or other interactions. In the composites, polymer-filler interactions can also take place through mechanochemical mechanisms. 

Yarns and fabrics are assemblages of fibers which have commercial application in the textile industry. The fabrics include those formed by weaving and also nonwovens. The geometry of the fabric, as well as the chemical composition of the polymer, influences mechanical properties and applications. The SEM is useful for evaluating (1) construction, (2) coverage, (3) uniformity, (4) surface structure and (5) effects of wear. 

Micro-Scratch Testing and Finite Element Simulation of Wear Mechanisms of Polymer Composites... 

Reinforced polymers are widely used in different tribological applications, such as rollers, bearings, gears, etc. The design or selection of these structural elements is usually based on experiences gained by specific wear tests. A theoretical approach for the better understanding of the wear mechanisms is not so common, due to the complexity of the wear process, the specific material behavior of the polymers, and the inhomogeneity of the composite materials used. 

The aim of the present chapter is to describe and to model the wear mechanisms of continuous fiher-reinforced polymer composites by using scratch tests, scanning electron microscopy, and finite element (FE) contact techniques applied to macro/micro-models, as well as a debonding algorithm developed. 

Figures 8 and 9 illustrate schematically the typical, experimentally observed wear mechanisms of the unidirectional fiber-reinforced polymer composites in the form of wear cycles based on different wear and scratch tests. Only the wear mechanisms of N- and P-fiber orientations are represented here because, in the case of AP-fiber orientation, they are similar to those observed for P-fiber orientation.

Figure 8. Typical wear mechanisms of a normally oriented unidirectional fiber-reinforced polymer composite.

K. Friedrich, Z. Zhang, P. Klein (2004) Wear of polymer composites, in Wear -Materials, Mechanisms and Practice (Ed. G. W. Stachowiak) The Institution of Mechanical Engineers, Professional Engineering Publishing Ltd., in press. 

Calundann GW (1979) Polyester of 6-hydroxy-2-naphthoic acid and para-hydroxy benzoic acid capable of readily undergoing melt processing. US Patent 4,161,470, 17 July 1979 Chang L, Friedrich K (2010) Enhancement effect of nanoparticles on the sliding wear of short fiber-reinforced polymer composites a critical discussion of wear mechanisms. Tribol Int 43 2355-2364... 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

Janes, Neumann and Sethna ° reviewed the general subject of solid lubricant composites in polymers and metals. They pointed out that the reduction in mechanical properties with higher concentrations of solid lubricant can be offset by the use of fibre reinforcement. Glass fibre is probably the most commonly used reinforcing fibre, with carbon fibre as a second choice. Metal and ceramic fibres have been used experimentally to reinforce polymers, but have not apparently been used commercially. To some extent powders such as bronze, lead, silica, alumina, titanium oxide or calcium carbonate can be used to improve compressive modulus, hardness and wear rate. 

A discussion of the wear of PTFE would not be complete without some reference to PTFE composites. This has been a popular field of study simply because without fillers the wear of PTFE is normally unacceptable. A good filler will reduce transfer wear rates by up to three orders of magnitude. Various mechanisms have been proposed and the subject has been reviewed by the present author (8,9) and others (2,52). The simplest idea is that fillers wear less than the polymer when exposed at the interface. They may also suppress transfer and improve transfer film adhesion, A good deal of effort of high quality has been put into the search for chemically induced adhesion promotion at the transferred film-substrate interface but the evidence is equivocal (53,54). Chemical changes are detected but their precise contribution to the adhesion is uncertain in commercial applications. PTFE is a remarkably stable polymer to chemical attack even at sliding interfaces. 

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