Surface Roughness Deformation Research Articles

Wear calculation and life prediction model of disc brake based on elastoplastic contact mechanics

For the friction and wear of the braking surface of the disc brake, the mechanism of friction contact deformation of rough surface is analyzed. Considering elastoplastic contact mechanics of the friction surfaces, combined with Archard wear calculation theory, a wear calculation model of fractal rough surface is established, and a wear life prediction of the brake disc is proposed. Based on high-speed and heavy-load braking conditions, the influence of different braking parameters on the surface wear of brake disc is studied. Moreover, a pin-on-disc wear test is used to verify the validity of the wear calculation model, and the average relative error of test and simulation is 4.97%. The research results show that the fractal parameters affect the complexity of the rough surface, and surface wear is mainly caused by interface plastic contact. The friction coefficient is large, which can strengthen the surface shear effect. Large load and high speed would increase the real contact area of the surface and increase the wear volume per unit time. Furthermore, the wear life of the brake disc could be estimated, which is of great significance for raising the wear life of the brake disc, improving braking life and braking efficiency.

Deformation of Rough Surfaces in Point EHL Contacts

The film thickness profile obtained by the optical interferometry technique merely represents a separation between contact surfaces and does not give the surface shape of contact surfaces. It has been pointed out that the actual shape of the surface roughness in rolling and/or sliding EHL contacts must be evaluated by separately obtaining the surface shape of contact bodies. The degree of the amplitude reduction in actual roughness depends on the mechanical properties of both contacting surfaces. That is, the deformation of roughness and the pressure at which roughness locates are controlled by the interrelationship between the rough surface and the mating surface caused by rolling and/or sliding motion. The method of finding surface profiles of both bodies separately and also the pressure distribution from the interferogram obtained by the optical interferometry technique is proposed in “Appendix”.

Plastic deformation of rough surface by a sliding tool

Modeling is carried out of the discrete plastic deformation of the rough surface of a metal part by a sliding rigid tool with a circular profile. This modeling is based on the theory of the plane deformation of a perfectly plastic solid taking into account the Prandtl contact friction. The number of discrete contacts and the plastic stress–strain state are determined by the periodic shape of the rough surface, as well as the radius and the vertical displacement of the tool with regard to asperity summits. The plastic smoothing mode used to reduce the surface roughness without the deformation of the core of the metal part is considered.

Numerical Modeling of Electrical Contact Conductance of Rough Bodies

Since the beginning of the 20th century to the present time, efforts have been made to develop a model of the electrical contact conductance. The development of micro- and nanotechnologies make contact conductance problem more essential. To conduct borrowing from a welldeveloped thermal contact conductance models on the basis of thermal and electrical conductivity analogy is often not possible due to a number of fundamental differences. While some 3Dmodels of rough bodies deformation have been developed in one way or another, a 3D-model of the electrical conductance through rough bodies contact is still not. A spatial model of electrical contact of rough bodies is proposed, allows one to calculate the electrical contact conductance as a function of the contact pressure. Representative elements of the bodies are parallelepipeds with deterministic roughness on the contacting surfaces. First the non-linear elastic-plastic deformation of rough surface under external pressure is solved using the finite element software ANSYS. Then the solution of electrostatic problem goes on the same finite element mesh. Aluminum AD1 is used as the material of the contacting bodies with properties that account for cold work hardening of the surface. The numerical model is built within the continuum mechanics and nanoscale effects are not taken into account. The electrical contact conductance was calculated on the basis of the concept of electrical resistance of the model as the sum of the electrical resistances of the contacting bodies and the contact itself. It was assumed that there is no air in the gap between the bodies. The dependence of the electrical contact conductance on the contact pressure is calculated as well as voltage and current density distributions in the contact bodies. It is determined that the multi-asperity contact mode, adequate to real roughness, is achieved at pressures higher than 3MPa, while results within the single contact spot are suitable for modelling a structured artificial roughness only.

Modeling of dry stiction in micro electro-mechanical systems (MEMS)

Stiction, a term commonly used in micro electro-mechanical systems (MEMS) to refer to adhesion, is a major failure mode in MEMS. Undesirable stiction, which results from contact between surfaces, can severely compromise the reliability of MEMS. In this paper, a model is developed to predict the dry stiction between uncharged micro parts in MEMS. In dry stiction the interacting surfaces are assumed to be either hydrophobic or placed in a dry environment. In this condition the van der Waals (vdW) and asperity deformation forces are dominant. Here a model is developed for the vdW force between rough micro surfaces, and the new model is combined with a newly developed multiple asperity point model for the elastic/plastic deformation of rough surfaces in contact to solve the equilibrium condition of the forces. This in turn will yield the equilibrium distance between micro surfaces, using which the apparent work of adhesion can be found. The theory result is compared with the available experimental data from the literature. The developed model can be easily used for design purposes. If the topographic data and material constants are known, the desirable adhesion parameters can be quickly found from the model.

Theoretical and experimental study of a thermal contact conductance model for elastic, elastoplastic and plastic deformation of rough surfaces

This study developed a thermal contact conductance model that takes into account surface asperities with elastic, elastoplastic and plastic deformation. The surface asperity model considers the continuity and smoothness of variables across different modes of deformation. Experiments were also conducted to measure thermal contact conductance for samples with different surface roughness when the contact pressure was increased or decreased. The trend of the test data supports the theoretical results.

An Analysis of the Elastic and the Plastic Deformation of Machined Surfaces in Contact : 2nd Report, Calculation and Experiment on Deformation of Rough Surfaces in Contact

An Analysis of the Elastic and the Plastic Deformation of Machined Surfaces in Contact : 2nd Report, Calculation and Experiment on Deformation of Rough Surfaces in Contact