Empirical Models for the Viscoelastic Complex Modulus with an Application to Rubber Friction

Up-to-date predictive rubber friction models require viscoelastic modulus information; thus, the accurate representation of storage and loss modulus components is fundamental. This study presents two separate empirical formulations for the complex moduli of viscoelastic materials such as rubber. The majority of complex modulus models found in the literature are based on tabulated dynamic testing data. A wide range of experimentally obtained rubber moduli are used in this study, such as SBR (styrene-butadiene rubber), reinforced SBR with filler particles and typical passenger car tyre rubber. The proposed formulations offer significantly faster computation times compared to tabulated/interpolated data and an accurate reconstruction of the viscoelastic frequency response. They also link the model coefficients with critical sections of the data, such as the gradient of the slope in the storage modulus, or the peak values in loss tangent and loss modulus. One of the models is based on piecewise polynomial fitting and offers versatility by increasing the number of polynomial functions used to achieve better fitting, but with additional pre-processing time. The other model uses a pair of logistic-bell functions and provides a robust fitting capability and the fastest identification, as it requires a reduced number of parameters. Both models offer good correlations with measured data, and their computational efficiency was demonstrated via implementation in Persson’s friction model.

Asperity-based modification on theory of contact mechanics and rubber friction for self-affine fractal surfaces

Modeling the real contact area plays a key role in every tribological process, such as friction, adhesion, and wear. Contact between two solids does not necessarily occur everywhere within the apparent contact area. Considering the multiscale nature of roughness, Persson proposed a theory of contact mechanics for a soft and smooth solid in contact with a rigid rough surface. In this theory, he assumed that the vertical displacement on the soft surface could be approximated by the height profile of the substrate surface. Although this assumption gives an accurate pressure distribution at the interface for complete contact, when no gap exists between two surfaces, it results in an overestimation of elastic energy stored in the material for partial contact, which typically occurs in many practical applications. This issue was later addressed by Persson by including a correction factor obtained from the comparison of the theoretical results with molecular dynamics simulation. This paper proposes a different approach to correct the overestimation of vertical displacement in Persson’s contact theory for rough surfaces with self-affine fractal properties. The results are compared with the correction factor proposed by Persson. The main advantage of the proposed method is that it uses physical parameters such as the surface roughness characteristics, material properties, sliding velocity, and normal load to correct the model. This method is also implemented in the theory of rubber friction. The results of the corrected friction model are compared with experiments. The results confirm that the modified model predicts the friction coefficient as a function of sliding velocity more accurately than the original model.

Friction lining coefficient of the drive friction pulley

Mine hoisting KOEPPE system or friction hoist winch work with traction pulley, the pulley rim grooves are lined. Lining has to provide a higher friction coefficient between the rope and the traction pulley. The constructors of mine hoisting machines require from the manufacturers a guaranteed appropriate and stabile value of a friction coefficient at different pressures between a rope and a friction lining under different external conditions (drought, moisture, icing, etc.). The paper presents processed measurements performed on the six samples of the friction lining (G1-G6) made of rubber and the sample of the standard used friction lining (K25). The samples (G1-G6) differ in the chemical composition of the rubber. Due to the confidentiality of the material composition of the friction linings the hardness of the lining material as a discriminator was chosen. The measured values of the friction coefficient of the rubber friction lining samples were compared with the values of the friction coefficient of the friction lining (K25) usually mounted on friction lining pulley.

Rubber Adhesion and Friction: Role of Surface Energy and Contamination Films

We study the influence of the surface energy and contamination films on rubber adhesion and sliding friction. We find that there is a transfer of molecules from the rubber to the substrate which reduces the work of adhesion and makes the rubber friction insensitive to the substrate surface energy. We show that there is no simple relation between adhesion and friction: adhesion is due to (vertical) detachment processes at the edge of the contact regions (opening crack propagation), while friction in many cases is determined mainly by (tangential) stick-slip instabilities of nanosized regions, within the whole sliding contact. Thus while the pull-off force in fluids may be strongly reduced (due to a reduction of the work of adhesion), the sliding friction may be only slightly affected as the area of real contact may be dry, and the frictional shear stress in the contact area nearly unaffected by the fluid.

Rubber Wear and the Role of Transfer Films on Rubber Friction on Hard Rough Substrates

We study the influence of rubber transfer films on the sliding friction between rectangular rubber blocks and a concrete surface. We present experimental results for the friction coefficient for a rubber compound sliding on a concrete surface contaminated by another rubber compound, for two different pairs (A, B) and (C, D) of rubber compounds. For the same rubber compounds, we present theory results which illustrate the relative importance of the viscoelastic and adhesive contribution to the sliding friction. We correlate the calculated rubber friction with the nature of the observed transfer films (or wear processes). Graphical Abstract

EXPEDIENCY OF USING FRICTION-BEARING ASBESTOS-RUBBER MATERIALS IN FRICTION UNITS

The article presents an analysis and comparison of friction elements consisting of Ferodo and retinax with asbestos-rubber friction material 143-63 and 8-45-62 in the nodes and brakes of forging and pressing machines operated at the factories of the forest and woodworking industry. In Russia, widely used friction materials Ferodo and retinax in the clutches and brakes of operating machines no longer satisfy consumers in many cases due to their low strength and wear resistance, which began to limit the performance of friction units. The analysis showed that the use of friction asbestos-rubber materials of grades 143-63 and 8-45-62 in the nodes and brakes of forging and pressing machines operated at the factories of the forest and woodworking industry, will dramatically increase both the productivity of machines and their performance, and also makes it possible to significantly reduce the cost of maintenance and repair of forging and pressing equipment.