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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.

This paper provides a comprehensive study of the nonlocality-influenced radiative modes above the light line in the plasmonic nonlocal flat surface, including the plasmonic/dielectric interface, ultrathin plasmonic slab, and plasmonic/dielectric multilayer. We demonstrate that material nonlocality arising from the longitudinal plasmon wave excited in plasmonic material dramatically alters the radiative mode above the light line, leading to the splitting of the Brewster mode in the dispersion relation diagram of the plasmonic slab. And material nonlocality together with structural nonlocality reveals novel discrete radiative modes in the high-frequency regime in the plasmonic/dielectric multilayer at subwavelength scales. Our results highlight the impact of material nonlocality and structural nonlocality on radiative modes in plasmonic flat structures and might contribute to new ideas in optical device design.

The contact of nominally flat surfaces can be treated as a bilateral periodic contact problem considering the stochastic surface similarity to the asperity distribution in a representative region. This similarity treatment method can be extended to material inhomogeneities. A novel numerical model for simulating the elastoplastic contact between nominally flat surfaces of materials containing inhomogeneities or coatings is developed via extending the concept of the discrete convolution and FFT (DC–FFT) algorithm with double superpositions of influence coefficients, which is named the DCSS–FFT algorithm. Several cases are analyzed with this new algorithm to examine its convenience, efficiency, and accuracy in dealing with complicated nominally flat–flat contact problems. The effects of surface roughness and material inhomogeneity are explored, and the mechanisms of contact surface failure are discussed.

The current paper is prepared with the objective of providing experimental evidence that the internal friction angle of rocks can be assessed using a scratch test with a blunt polycrystalline diamond compact (PDC) cutter. For this purpose, a comprehensive set of cutting experiments was carried out to determine the wear flat-rock friction coefficient in two limestones and one coarse-grained sandstone using state-of-the-art scratch based rock cutting equipment. Additional triaxial compression (TC) experiments were conducted on specimens of these rock formations, and a Coulomb failure analysis was conducted to independently estimate the internal friction coefficient of each specimen. The experimental results indicate that the value of internal friction angle (intrinsic rock property) derived from TC experiments is related to the apparent friction angle at the wear flat-rock interface of the blunt PDC cutter when the wear flat surface is inclined at inclination angles ranging between 0∘ to 1∘. Further, new results on one rock specimen were obtained by performing novel scratch tests with blunt PDC cutters with different wear flat properties, showing that the apparent friction angle at the wear flat-rock interface of a blunt cutting tool is significantly affected by the wear flat roughness and the wear flat material properties.HighlightsA new method was introduced to measure the internal friction angle of rock samples using rock cutting/drilling data.An extensive set of cutting experiments was conducted using different PDC blunt/worn cutters.The internal friction angle of rock specimens were obtained using triaxial compressrion (TC) tests.The internal friction angles of rock specimens were related to the apparent friction angles at the wear flat-rock interface when the wear flat surface is parallel to the rock free surafce.The wear flat properties of the PDC cutters have a significant effect on the apparent friction angle.

There are various situations of drop impact on solid surfaces widely occurred in natural phenomenon or used in different industrial applications. However, comparing and classifying these drop impact situations is not easy due to different states of the parameters affecting drop impact dynamics. In this article, a unified transformation framework is proposed to study various situations of vertical/oblique drop impact on horizontal/inclined stationary/moving flat surfaces with/without a crossflow. This simple framework consists of a coordinate with normal and tangential axes on a horizontal stationary surface. For each drop impact situation, the drop velocity, gravitational acceleration, possible induced flow due to the moving surface, and possible crossflow are transformed into the framework. Comparing the transformed versions of considered drop impact situations facilitates identification of their physical similarities/differences and determines which situations (and under what conditions) lead to identical results and can be used interchangeably. Although common situations of drop impact on moving surfaces (having tangential component of surface velocity) lead to asymmetric drop spreading, the possibility of symmetric drop spreading on moving surfaces is demonstrated and analyzed using the proposed transformation framework. This interesting possibility means that for related production lines or experimental setups, where symmetrical drop spreading is required, the surface does not need to be stationary. In such applications/setups, the use of moving surfaces (rather than stationary surfaces) can considerably accelerate the symmetric drop impact process. Our simulation results of several of the considered drop impact situations well confirm the facilities/predictions of the proposed transformation framework.

Thermal contact resistance (TCR) plays a pivotal role in heat transfer across diverse engineering applications. The present work systematically investigates TCR for two representative contact configurations, namely flat and hinge-type curved surfaces, under varied conditions of temperature, pressure, and surface roughness. A high-precision steady-state heat flux experimental system was designed, integrating heating, cooling, and pressure-loading subsystems to ensure controlled operation conditions. The experimental results revealed that TCR decreases with rising contact temperature and pressure, while it increases significantly with surface roughness. And the surface roughness exerts the most dominant influence. The effect of pressure on TCR is relatively minor at smaller surface roughness, whereas the pressure dependence becomes more significant at larger roughness. Empirical correlations for TCR as functions of contact pressure, roughness, and temperature were formulated for both flat and curved surface contacts based on the experimental data. The maximum fitting errors of the correlations are 6% for flat surface contact and 9.2% for curved surface contact, which demonstrates the reliability of the fitting results. These relationships enable the theoretical calculation of TCR for both flat and curved surface contacts under varying operating conditions.

The present work aimed to develop a simple simulation tool to support studies of slip and other non-traditional boundary conditions in solid–fluid interactions. A mesoscale particle model (movable automata) was chosen to enable performant simulation of all relevant aspects of the system, including phase changes, plastic deformation and flow, interface phenomena, turbulence, etc. The physical system under study comprised two atomically flat surfaces composed of particles of different sizes and separated by a model fluid formed by moving particles with repulsing cores of different sizes and long-range attraction. The resulting simulation method was tested under a variety of particle densities and conditions. It was shown that the particles can enter different (solid, liquid, and gaseous) states, depending on the effective temperature (kinetic energy caused by surface motion and random noise generated by spatially distributed Langevin sources). The local order parameter and formation of solid domains was studied for systems with varying density. Heating of the region close to one of the plates could change the density of the liquid in its proximity and resulted in chaotization (turbulence); it also dramatically changed the system configuration, the direction of the average flow, and reduced the effective friction force.

We focus on investigating the differential geometric properties of cuspidal edge in the three-sphere from a viewpoint of duality. Using Legendrian duality, we study a special kind of flat surface along cuspidal edge in three-dimensional sphere space. This kind of surface is dual to the singular set of the cuspidal edge surface. Thus, we call it the flat Δ -dual surface. Flatness of a surface can be defined by the degeneracy of the dual surface. It is similar to the case for the Gauss map of a flat surface in Euclidean space. Moreover, classifications of singularities of the flat Δ -dual surface are shown. We also investigate the dual relationships of singularities between flat Δ -dual surface and flat approximations of the original cuspidal edge surface. At last, we consider a global geometry of the singular set of a cuspidal edge surface using the flat Δ -dual surface.

A wideband circularly polarized rectangular dielectric resonator antenna (DRA) fed by a single feeding mechanism has been studied theoretically and experimentally. The purpose of the study is to determine how adding a parasitic strip next to the flat surface metallic feed would affect various far- and near-field antenna characteristics. Initially, the basic antenna design, i.e., the T-shape feed known as antenna A, produced a 4.81% impedance matching bandwidth (|S11| −10 dB). Due to the narrow and undesirable results of the initial antenna design, antenna-A was updated to the antenna-B design, i.e., Yagi-Uda. The antenna-B produced a decent result (7.89% S11) as compared to antenna-A but still needed the bandwidth widened, for this, a parasitic patch was introduced next to the Yagi-Uda antenna on the rectangular DRA at an optimized location to further improve the results. This arrangement produced circular polarization (CP) waves spanning a broad bandwidth of 28.21% (3.59–3.44 GHz) and a broad impedance |S11| bandwidth of around 29.74% (3.71–3.62 GHz). These findings show that, in addition to producing CP, parasite patches also cause the return loss to rise by a factor of almost three times when compared to results obtained with the Yagi-Uda-shape feed alone. Computer simulation technology was used for the simulation (CST-2017). The planned antenna geometry prototype was fabricated and measured. Performance indicators show that the suggested antenna is a good fit for 5G applications. The simulated outcomes and measurements match up reasonably.

The research is devoted to the elaboration of the wear part contact estimation using 3D surface texture parameters defined in the standard ISO 25178-2:2012 for contact (it is known that elastic contact gives less wear rate) area, friction, and wear rate determination. In our research, the sphere and random flat surface model was used, where the height of surface asperities h(x, y) had a normal probability distribution. As a result of research, the equations for estimation of the elastic contact area were derived and, we obtained conditions at which it was possible to use equations for flat random surfaces. The results of this study could have wide practical application, for example, in design, choosing the geometrical and physical-mechanical parameters of the parts, calculation of real stresses, wear rate and life time of contact parts, etc.