Contact Model Of Single Asperity Research Articles

A Complete Single Asperity-Based Statistical Gaussian Rough Surface Contact Model

Understanding the corrosion behavior of rough surface contacts needs the contact interaction of rough surfaces at asperity level. Generally, single asperity-based statistical rough surface contact model is predominating one in exploring contact behavior of rough surfaces. The FEM-based single asperity contact model is being used extensively to explain the elastic, elastic–plastic, and fully plastic behavior of the rough surface contacts. The empirical expressions to calculate the exact transitions (elastic to elastic–plastic and elastic–plastic to fully plastic states) are still incomplete. The earlier FEM-based single asperity contact models didn’t give mathematical expressions to exactly calculate the elastic, elastic–plastic, and fully plastic transition states by accounting the combined effect of material properties. In this way, in the present work, empirical expressions are developed to calculate the exact transitions of elastic, elastic–plastic and fully plastic states by accounting the combined effect of Young’s modulus, material yield strength, and Poisson’s ratio. The empirical expressions to calculate the dimensionless contact load and contact area are developed for elastic, elastic–plastic, and fully plastic states in terms of dimensionless interference, E/Y ratio, and Poisson’s ratio. Further, it is observed that the plasticity index is not a complete parameter to explore the contact behavior of rough surface contacts. In high surface plasticity index case, the material properties influence significantly compared to the low surface plasticity index case. The Poisson’s ratio significantly influences in low E/Y ratio materials in all the surface plasticity index cases.

Research on the loading–unloading fractal contact model between two three-dimensional spherical rough surfaces with regard to friction

A loading–unloading fractal contact model between two three-dimensional spherical rough surfaces with regard to friction is developed. The contact model of single asperity for the load–unload cycle with regard to friction is obtained. The expressions between contact load and real contact area in the loading and unloading processes in different deformation stages of three-dimensional spherical contact surfaces are deduced. The impacts of some parameters in the model are discussed by numerical analysis. The numerical results show that the critical contact load and the critical real contact area in different deformation stages of spherical contact surfaces with friction are positively related to the fractal dimension and the curvature radius, negatively correlated with the fractal roughness, influenced by the contact type. In the elastoplastic stage of spherical contact surfaces with friction, the real contact area in the unloading process is larger than that in the loading process with the same contact load; for a given contact load, the real contact area of the loading–unloading process, as well as the differences of the real contact area in the loading–unloading processes, increases with the increase in the fractal dimension and the curvature radius, decrease in the fractal roughness, or the substitution of internal contact for external contact.

A complete elastic-plastic spherical asperity contact model with the effect of isotropic strain hardening

Understanding the deformation behavior of rough surface contacts is essential to minimise the tribological consequences of contacts. Mostly, statistical, deterministic and fractal approaches are adopted to explore the contact of rough surfaces. In statistical approach, a single asperity contact model is developed and extended to the whole surface. In the present work, a deformable spherical asperity contact with a rigid flat is modeled and analysed by accounting the combined effect of Young’s modulus, Poisson’s ratio, yield strength and isotropic strain hardening rate using finite element method. The results reveal that the elastic, elastoplastic and plastic contact states are highly influenced by E/Y ratio and strain hardening rate followed by Poisson’s ratio. The dimensionless contact radius is an inadequate parameter to explore the combined effect of material properties. For all E/Y ratio and Poisson’s ratio, as the strain hardening rate increases, the dimensionless contact area decreases for the same dimensionless contact load at elastoplastic and fully plastic contact states. As the strain hardening rate increases, the fully plastic contact state is reached at low dimensionless interference compared to elastic perfectly plastic materials for all E/Y ratio and Poisson’s ratio. For a common elastic-plastic material, empirical relations are developed to calculate the contact load and contact area appropriately with E/Y ratio, Poisson’s ratio and interference ratio as input variables. It can be utilised to study the interaction of rough surface contacts for most of the practical materials.

A modified elastic contact stiffness model considering the deformation of bulk substrate

Establishing an accurate and effective stiffness model of the elastic contact surface is the basis for further modeling and analysis of machine tool dynamics. In this paper, a new elastic contact stiffness model is proposed that considers the bulk substrate deformation and modifies the Greenwood and Williamson microcontact model (GW model) of rough surfaces. Based on the Hertz contact theory and fixed-point iteration method, a single asperity contact model is created to analyze the effects of bulk substrate deformation and coating materials. To make the contact stiffness model more accurate and effective, two aspects are improved: One is to introduce the triangular distribution function to make the asperity heights distribution more consistent with the actual machined surface, and the other is to correct the defects in the micro-contact process. Comparing the finite element simulation results with the modal test data, the correctness of the proposed contact stiffness model is verified. The simulation results reveal the influence of distribution function, surface roughness and coating material on the contact characteristics of the joint surface.

A study of elastic–plastic contact of statistical rough surfaces

In this article, a study of elastic–plastic contact of statistical rough surfaces is presented. The contact behaviors of a single asperity with deformable substrate are studied by finite element method. The influences of material properties and substrate deformation on the single asperity contact behaviors are investigated. An elastic–plastic contact model of rough surfaces is established based on the proposed single asperity contact model and statistical rough surface contact model. The surface topography plasticity index and material plasticity index are defined to indicate the influences of surface topography and material properties on the contact behaviors of rough surfaces. Comparisons with some exiting models and finite element results show that the proposed formulations can model the single asperity contact behaviors well for a wide interference range. The rough surface contact model in this work is consistent with some existing models for small plasticity indices, and it is slightly different from the existing models for large plasticity indices. The increase of surface topography plasticity index and material plasticity index would result in larger contact area and contact load for given separations.

Comparative Contact Analysis Study of Finite Element Method Based Deterministic, Simplified Multi-Asperity and Modified Statistical Contact Models

The study of the contact stresses generated when two surfaces are in contact plays a significant role in understanding the tribology of contact pairs. Most of the present contact models are based on the statistical treatment of the single asperity contact model. For a clear understanding about the elastic-plastic behavior of two rough surfaces in contact, comparative study involving the deterministic contact model, simplified multi-asperity contact model, and modified statistical model are undertaken. In deterministic contact model analysis, a three dimensional deformable rough surface pressed against a rigid flat surface is carried out using the finite element method in steps. A simplified multi-asperity contact model is developed using actual summit radii deduced from the rough surface, applying single asperity contact model results. The resultant contact parameters like contact load, contact area, and contact pressure are compared. The asperity interaction noticed in the deterministic contact model analysis leads to wide disparity in the results. Observing the elastic-plastic transition of the summits and the sharing of contact load and contact area among the summits, modifications are employed in single asperity statistical contact model approaches in the form of a correction factor arising from asperity interaction to reduce the variations. Consequently, the modified statistical contact model and simplified multi-asperity contact model based on actual summit radius results show improved agreement with the deterministic contact model results.

Influence of the Solvent Environment on the Contact Mechanics of Tip−Sample Interactions in Friction Force Microscopy of Poly(ethylene terephthalate) Films

Friction force microscopy measurements have been carried out on free-standing films of poly(ethylene terephthalate) in a variety of different media. In ethanol, the adhesion force was small, and the friction-load relationship was linear. In perfluorodecalin, nonlinearity was observed in the friction-load relationship, and the data have been found to fit the Johnson-Kendall-Roberts model of contact mechanics. The behavior in hexadecane was also characterized by a single-asperity contact model, but in this case, the data were found to fit the Derjaguin-Müller-Toporov model. It is suggested that these differences are due to the different strengths of tip-sample adhesion, which arise from the differences in the dielectric constants of the media: in ethanol, which has a high dielectric constant, the friction force varies linearly with the load, whereas in media of low dielectric constant, adhesion-limited behavior is observed.