This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adhesion between indenter and substrate, were specified so that diverse quantities of interest, e.g., the distribution of interfacial stresses at a given load or the mean gap as a function of load, could be computed and compared to a reference solution. Many different solution strategies were pursued, ranging from traditional asperity-based models via Persson theory and brute-force computational approaches, to real-laboratory experiments and all-atom molecular dynamics simulations of a model, in which the original assignment was scaled down to the atomistic scale. While each submission contained satisfying answers for at least a subset of the posed questions, efficiency, versatility, and accuracy differed between methods, the more precise methods being, in general, computationally more complex. The aim of this paper is to provide both theorists and experimentalists with benchmarks to decide which method is the most appropriate for a particular application and to gauge the errors associated with each one
Contact is one of the main means to transmit force between bodies, and a detailed study of contact mechanics provides the required knowledge toward a realistic prediction of the behavior of contacting bodies. In this study, an approach based on the Greenwood-Williamson model is developed in which all of the contact points on the contacting surfaces are observed momentarily. The surface roughness is experimentally measured. The surface asperities are treated as spline functions, and their properties such as radius of curvature are obtained by differentiating these functions. The response of each individual contact point is evaluated by solving contact equations related to a specific asperity in elastic, elastoplastic, and plastic regimes. The method is therefore called spatially resolved Greenwood-Williamson (SRGW) model. To validate the model, a new technique is used which is based on indentation. A series of indentation experiments are conducted on two contacting surfaces, and the elastic and plastic deformations of the asperities under different loads are measured. The percentage error of the proposed approach is lower compared to other methods such as GW and ZMC, which shows the higher accuracy of this new method. The results show that the presented model can predict experimental results with reasonable accuracy under different contact conditions.
Shape memory alloys (SMA) are nowadays widely used in different industries. The two extraordinary behaviors of superelasticity and shape memory effect make these alloys a super wear-resistant material. In a range of SMA applications, contact between adjacent surfaces occurs. In this research, a formerly-developed contact model, which individually considers each asperity, is extended to cases where superelastic shape memory alloys are used. Since constitutive equations of SMAs are based on stress and strain, to establish a relationship between classical contact models and the main arguments of these constitutive equations, a representative strain based on the pseudoelastic behavior of SMAs was defined. Experiments were conducted to verify the model’s predictions. In these experiments, a NiTi wire was pressed against a Steel plate; then, the measured penetration in the test and the values predicted by the contact model were compared. The reported results show an acceptable agreement between theory and experiment.
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