There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

It is realized that the addition of a small percentage of rigid nanoparticles to polymers significantly improves many of their mechanical properties, especially stiffness and strength. Such improvements are often attributed to the availability of large numbers of nanoparticles with huge interfacial areas compared to their macro- and micro-scale counterparts. In particular, from the tribological viewpoint, the small size of nanoparticles with homogenous dispersion in the matrix and good interfacial adhesion between nanoparticles and matrix are thought to be necessary requirements for a polymer nanocomposite. Material removal will be less since the nano-additives have similar sizes to the segments of surrounding polymer chains. Despite these positive effects due to the addition of nanoparticles, there are still some critical questions that are unanswered. Here, we review the fundamentals, recent progress and advances that have been made on the tribological aspects of polymer nanocomposites, particularly focusing on their wear (in dry sliding and unlubricated conditions) and scratch damage. The review shows that (a) it is not valid to assume that nano-fillers always improve wear/scratch (and friction) properties; and (b) material properties like modulus, hardness, fracture toughness or extent of wear rate or scratch penetration depth are not the sole indicators to compare and/or rank candidate materials. Several facets of wear/scratching or material response to the sliding processes require thorough understanding in order to determine parameters that control the surface integrity and material removal from polymer nanocomposites. This review also shows the apparent contradictions and false impressions on several material systems in many studies owing to poor characterizations of polymer nanocomposites and lack of quantitative descriptions of the observed phenomena.

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Fundamental aspects and recent progress on wear/scratch damage in polymer nanocomposites

Friction and wear characteristics of ultrahigh molecular weight polyethylene (UHMWPE) composites containing glass fibers and carbon fibers under dry and water-lubricated conditions

A novel type of polyoxymethylene (POM)-based composites with polytetrafluoroethylene (PTFE) fiber and poly(ethylene oxide) (PEO) was prepared via melt extrusion in order to enhance the friction lubrication and wear resistance of POM. The tribological experiments demonstrated that the coefficient of friction and wear rate of POM were both reduced by the incorporation of PTFE fiber, and furthermore, the higher the loading of PTFE fiber the better the tribological properties. The wear mechanism is derived from the thin film of PTFE formed on the contact-surfaces during sliding. The addition of PEO into POM/PTFE fiber composites can enhance the formation of transfer film on the mating surfaces during sliding contact, and thus further improves the friction and wear performance. The wear behaviors also depend on the normal loading and sliding duration, under which the transfer film could form appropriately. In addition, the abrasion of the dispersed PEO domains in matrix is also helpful to the heat dissipation when the counter-surface exerts oscillating forces on the POM surface. It should be emphatically mentioned that the use of PTFE fiber as tribological additive can improve the notched impact strength of POM, and the subsequent incorporation of PEO leads to a more significant toughening effect for POM. The morphological investigation reveals that the toughening effect is attributed to the dissipation of impact energy through the pullout of PTFE fiber and the plastic deformation of the POM matrix induced by PEO. Polarized optical microscopy demonstrates that the presence of PEO can interfere in the crystallization of POM and reduced the size of spherulites, and consequently weakened the sensitivity to notch. Although the POM-based composites underwent a different mode of thermal degradation from neat POM with a slight reduction in the temperature at rapid weight loss, their thermal stabilities were maintained well enough to meet the requirement for its application.

Effect of poly(ethylene oxide) on tribological performance and impact fracture behavior of polyoxymethylene/polytetrafluoroethylene fiber composites

Austempered irons and steels offer the design engineer alternatives to conventional material/process combinations. Depending on the material and the application, Austempering may provide the following benefits to producers of powertrain components such as gears and shafts: ease of manufacturing, increased bending and/or contact fatigue strength, better wear resistance and enhanced dampening characteristics resulting in lower noise. Austempered materials have been used to improve the performance of powertrain components in numerous applications for a wide range of industries, from gears and shafts to clutch plates and crankshafts. This paper focuses on Austempered solutions for powertrain applications with an emphasis on gear and shaft solutions.

/pdf/austempered-materials-for-powertrain-applications-3drupmbvyw.pdf

Austempered Materials for Powertrain Applications

One of the main gear damage mechanisms is the formation of pitting and spalling on the tooth flank. Several factors have significant influence on the damage formation, such as: contact stress level; tooth profile type; relative contact speed; surface finish and lubrication conditions. This work comprehends the global observation of all such parameters and was carried out to explain the phenomena related to this wear mechanism. The wear test equipment uses the power recirculation principle and is commonly known as FZG test rig. The gears were made from AISI 8620 steel and had two types of surface finishing (by shaving or by milling). The wear experiments were performed with two torque stages: 135 N.m (running-in) and 302 N.m (steady-state), and two test temperatures: 60oC (running-in) and 90oC (steady-state). The wear level was determined by using image analysis. In order to calculate the specific film thickness and friction coefficient, the roughness of tooth flank was measured at each test stop. After the experiments were completed, it was possible to confirm that, for both manufacturing processes, the boundary lubrication regime was adopted at the tooth flank and the specific film thickness presents a different behavior when compared to addendum, pitch diameter and deddendum regions. The wear on the gear flanks depended on the lubricant film thickness and it was higher for the milled gears.

/pdf/the-influence-of-contact-stress-distribution-and-specific-1vtpx8w2k9.pdf

The influence of contact stress distribution and specific film thickness on the wear of spur gears during pitting tests

Development of severity parameter for wear study of thermoplastics

Is there delamination wear in polyurethane

This work presents a tribological evaluation of the influence of graphite and bronze fillers in two commercial composites in a dry sliding pin-on-disc test at the same contact severity (PVa paramet...

Effect of Graphite and Bronze Fillers on PTFE Tribological Behavior: A Commercial Materials Evaluation

It is discussed the use of ADI (Austempered Ductile Iron) for gears. The gears were produced from continuous cast iron bars, heat treated for grade 3 of ASTM ADI Standard A897M06 (UTS >1200 MPa), and compared to carburized steel AISI 8620 and to induction hardened steel AISI 4140. Tests on gears were made using equipment developed at UTFPR, measuring the time for pitting and spalling on the surface of the gears. The results show very good potential of using ADI for gears, replacing induction hardened steels. The results show too that the nodule size affects the life of gears, independently of the mechanical properties of the matrix. The ADI with smallest nodules show higher life for pitting formation. It is discussed additionally the mechanisms of crack propagation under the surface of the gears, for all tested materials.

http://www.tupy.com.mx/downloads/guesser/adi-engrenagens.pdf

Carlos Henrique da Silva

Papers

The influence of contact stress distribution and specific film thickness on the wear of spur gears during pitting tests

Development of severity parameter for wear study of thermoplastics

Is there delamination wear in polyurethane

Effect of Graphite and Bronze Fillers on PTFE Tribological Behavior: A Commercial Materials Evaluation

Austempered Ductile Iron for Gears