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It is well known that elastomers usually possess poor dry sliding friction properties due to their highly adhesive character. In order to overcome this problematic behavior in industrial applications, interfacial materials such as oils, greases, coatings, or lacks are normally used in order to separate or to functionalize the contact surfaces of elastomers. Alternatively, the high adhesion tendency of elastomers may be explicitly reduced by modifying the elastomer composition itself or by enabling a reduction of its effective contact area through, for example, surface laser texturing. This second approach, i.e., the reduction of the adhesive character of elastomers through laser structuring, will be the main topic of the present study. For this purpose, different micro-sized grooved structures were produced on flat injection molds using an ultra-short pulsed laser. The micro-structured molds were then used to produce injection molded micro-ridged Liquid Silicone Rubber (LSR) sample pads. The investigations consisted firstly of determining the degree of replication of the mold micro-structures onto the surface of the LSR pads and secondly, to ascertain the degree of reduction of the friction force (or coefficient of friction) of these micro-ridged LSR pads in comparison to the benchmark (unstructured LSR pads) when tested under dry conditions against Aluminum alloy (Al-6082) or PA6.6-GF30 plates. For this second part of the investigation, the normal force (or contact pressure) dependency of the coefficient of friction was determined through stepwise load increasing friction tests. The results of these investigations have shown that the production of micro-ridged surfaces on LSR pads through laser structuring of the injection molds could be successfully achieved and that it enables a significant reduction of the friction force for low normal forces (or contact pressures), where the component of adhesion friction is playing an important and determining role in the overall friction behavior of the LSR elastomer. [ABSTRACT FROM AUTHOR]

In the present study, PA6 polymers with and without solid lubricant inclusions were investigated against S1100QL steel surfaces that had different surface roughness values—a very high surface roughness (Rz ≈ 40 µm) and a low surface roughness (Rz ≈ 5 µm). Static and dynamic friction coefficients were analysed under a series of nominal contact pressures (2.5 to 40 N/mm2) considering the influences of polymer water saturation, temperature, counter-body surface roughness and lubrication. Mechanisms for the observed influences of the respective parameters are provided and are interpreted from the view of the adhesive and deformative contributions to the friction force. [ABSTRACT FROM AUTHOR]

This paper presents a systematic procedure for the development of a constitutive model of friction with focus on the application in bulk metal forming simulations. The empirically based friction model describes friction as a function of sliding distance and the most relevant friction influencing parameters. The latter were determined by means of designed experiments. An optimal friction model is obtained as a trade-off between model accuracy and complexity by using stepwise nonlinear regression and a modified version of the Akaike information criterion. Within this study, the procedure is applied to determine a friction model for tube drawing. However, the same approach can also be used for modeling friction of any other bulk metal forming process. [ABSTRACT FROM AUTHOR]

Total electron yields from highly oriented pyrolytic graphite (HOPG) have been measured for perpendicular impact of H+, C+, N+, and O+ projectile ions with kinetic energies from a few hundred eV up to 30 keV. The data are interpreted within a model for kinetic electron emission based on non-adiabatic time-dependent perturbation of valence-band electrons by the moving particle. The microscopical parameters of this excitation processes describe well the qualitative trends in the experimental data when changing the target from HOPG to polycrystalline gold. [Copyright &y& Elsevier]