Search

Real contact area plays a critical role in tribology. However, few contact models can give accurate load-area relation at very large contact fraction due to the lack of asperity interactions. In this work, an improved Greenwood–Williamson model is advanced for elastic–plastic rough surfaces. To include the asperity interactions in a simple way, the random distribution of contacting spots is treated as hexagonal distribution, which possesses the same overall isotropic property on surface. A representative asperity is then simulated by finite element method, and the load-area relation is calculated up to almost full contact. It is found that surface morphology and material properties govern the initial linear relationship at small contact fraction, and the interactions among asperities are closely related to contact fraction and lead to a larger load than that neglecting asperity interactions. The load-area relation is further formulated for general rough surfaces by comparing with an incremental equivalent contact model at initial contact. Direct simulations on typical rough surfaces verify the accuracy of the advanced load-area relation within a large range of contact fraction. This result provides a foundation for further analysis of friction, wear and sealing in tribology. [ABSTRACT FROM AUTHOR]

Accurate relation between load and area is of great interest in tribology, especially for large contact fraction, in which the asperity interactions play an import role. The constant mean contact radius obtained in the original Greenwood–Williamson model is adopted in this work; Then, the asperity interactions are dealt with by arranging the random distributed contact spots to hexagon distribution. Finite element simulation is employed to consider only a representative unit with symmetrical boundary conditions, and the corresponding load-area relation is determined up to almost complete contact. For a given contact fraction, interactions induce larger load compared to the GW model without asperity interactions. Furthermore, by comparing with the analytical result given by an incremental contact for small contact fraction, the obtained load-area relation is extended to a general formulation, which shows good agreement with direct finite element simulations. The obtained relations are more general and applicable for a large range of contact fraction. This model provides an efficient method to predict the overall contact response of rough surfaces and reduces the computational burden greatly. [ABSTRACT FROM AUTHOR]

It is now commonly accepted that real contact area rises linearly with increasing normal load for the contact of rough solids. However, the coefficient of proportionality is distinct in various models and simulations. This study advances a general method to determine the area-load proportionality based on the incremental contact concept. A pair of loose bounds on the coefficient of proportionality for general Gaussian random rough surfaces and a tight one working in the thermodynamic limit are derived. The resultant predictions are in accord with numerical results presented in literature. The current study might offer some deep insight into the role of surface morphologies in contact of rough elastic solids. [Display omitted] • An incremental contact model is proposed for the contact of rough elastic solids. • The role of asperity shape in contact deformation is studied. • Bounds on the proportionality between contact area and normal load are derived for various rough surfaces. • The applicability of the current model is verified by comparisons with simulation results in literature. [ABSTRACT FROM AUTHOR]

• An apparatus for in-situ measurement of interfacial separation is designed. • Evolutions of separations are recorded for flattening rough metallic samples. • Variations of the average separations in loading–unloading circles are discussed. • A piecewise power-law dependence of interfacial stiffness on loads is observed. The direct measurement of interfacial separation between rough solids is hitherto one of the most challenging tasks in contact mechanics. This paper develops an optical interferometric technique for in-situ measuring interfacial separation with nanoscale precision. For the contact of metallic samples, the evolutions of interfacial separation and stiffness with load are measured. In the loading process, the dependence of interfacial stiffness on load can be described by a power law with the exponent smaller than unity at low loads and larger than unity at large loads. Similar relations have been found for unloading but interrupted with a linear relation at intermediate loads. These characteristics are significantly different from those known for rough elastic solids, and provide new insights in tribology. [ABSTRACT FROM AUTHOR]

• An incremental contact model is proposed for the contact of rough viscoelastic solids. • The real contact area and the average interfacial separation are predicted for a loading-unloading circle. • An analytic solution is derived for standard linear solids with gaussian random rough surfaces under harmonic loading. • The role of surface roughness in viscoelastic energy dissipation is studied. Viscoelastic dissipation is long concerned to be one of the origins of kinetic friction. In this study, the viscoelastic contact of rough solids is investigated by combining the principle of Lee and Radok and a recently developed incremental contact model. Evolutions of the real contact area and the average interfacial separation are obtained for a loading-unloading circle. For standard linear solids with Gaussian random rough surfaces, the effects of the viscoelastic reduction ratio and the loading rate on the contact responses are discussed. The viscosity of contacting solids would lead to the hysteresis of the mechanical responses to external excitation. Based on the relation between the average interfacial separation and the normal load, the viscoelastic energy dissipation is calculated and the role of surface morphology is addressed. Generally, the dissipated energy is proportional to the root-mean-square height of the rough surface, but decays for surfaces with larger root-mean-square slopes. The results of the current study are helpful for studying the friction between solids. [Display omitted] [ABSTRACT FROM AUTHOR]

It is of critical significance to accurately measure or predict the real contact areas between rough solids in engineering. In this study, based on the frustrated total internal reflection technique and an Otsu method, an optical apparatus is designed to capture the real contact areas between rough metallic samples and flat quartz glass. Moreover, an incremental equivalent contact model developed recently by our group is adopted to predict the load-area relationship. For samples of various materials and morphologies, it is found that the proposed contact model agrees well with the experimentally measured results, which verifies the efficiency of the incremental equivalent contact model. [Display omitted] • The real contact area was measured using the optical method. • With morphology of rough samples, theoretical prediction was calculated. • The region and the area in contact from experiment and model are in consistence. • The influence of topography and material on the contact response was discussed. [ABSTRACT FROM AUTHOR]