Analytical stresses in rough contacts

2010 ◽  
Vol 225 (2) ◽  
pp. 274-279 ◽  
Author(s):  
P Sainsot
Keyword(s):  
Shear Stress ◽  
Rough Surfaces ◽  
Maximum Shear Stress ◽  
Failure Mechanisms ◽  
Pressure Fluctuations ◽  
Roughness Parameters ◽  
Near Surface ◽  
Local Stresses ◽  
Wavy Surfaces ◽  
Analytical Expressions

The pressure distribution generated by rough surfaces contact induces high stresses just beneath the surface. These stresses are at the origin of several failure mechanisms such as wear, crack initiation, etc. Therefore, it is important to be able to predict these stresses. This article describes an analytical model to evaluate the near surface stresses below a wavy surface. The originality of this work is to combine Herztian stresses in the general case of elliptical contacts and local stresses due to the pressure fluctuations. Furthermore, in case of wavy surfaces simple analytical solutions permit the calculation of the maximum shear stress and its location. Compared to a fully numerical method, the time of calculation is negligible; moreover, the analytical expressions give one the possibility of a better understanding of the effect of roughness parameters such as the wavelength of the asperities. Using a Fourier transform the results can be applied to rough surfaces.

scholarly journals Aging Effect on Structure, Hardness, Roughness Behavior and Bacterial Adhesion on Silver- Palladium Dental Alloy

2020 ◽  
pp. 1-3
Author(s):  
Abu Bakr El-Bediwi ◽  
◽  
Doaa Al- Ragae ◽  
Thoraya El-Helaly ◽  
◽  
...  
Keyword(s):  
Shear Stress ◽  
Bacterial Adhesion ◽  
Maximum Shear Stress ◽  
Aging Effect ◽  
Base Line ◽  
Palladium Alloy ◽  
Dental Alloy ◽  
Roughness Parameters ◽  
Candida Spp ◽  
Silver Palladium

Aging in normal saliva for different interval times make a change in internal structure (Formed phases and started base line) of Sliver- Palladium (Ag-Pd) dental alloy. Also aging in saliva for one, two and three weeks decreased Vickers hardness value, calculated maximum shear stress (τm) and roughness parameters for Sliver- Palladium alloy. Microbiological studies show the Candida spp. stuck on Sliver- Palladium alloy surface and their growth dependent on aging times.

scholarly journals Effect of annealing on creep behavior, hardness, roughness and electrochemical corrosion parameters of Co- Cr based alloy

2017 ◽  
pp. 5062-5068
Author(s):  
A. El Bediwi ◽  
Eman Kashita ◽  
Salah. M M.Salman
Keyword(s):  
Shear Stress ◽  
Corrosion Resistance ◽  
Corrosion Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Vickers Hardness ◽  
Maximum Shear Stress ◽  
Electrochemical Corrosion ◽  
Dental Alloy ◽  
Roughness Parameters

In the present work, the effect of annealing on creep behavior, hardness, maximum shear stress, roughness and electrochemical corrosion parameters of commercial Co64Cr29Mo6.5A0.5 (A= C, Si, Fe, and Mn) dental alloy from Travagliato (BS) - Italy have been studied and analyzed.  Creep behavior was studied by indentation and stress exponent was determined by Mulheam-Tabor method.  The results show that, Vickers hardness of Co64Cr29Mo6.5A0.5 alloy decreased but roughness parameters varied after annealing for two hours at 700, 800 and 900 °C.  Also the corrosion resistance in 0.5M HCl of Co64Cr29Mo6.5A0.5 alloy is increased but the corrosion rate with 0.5M HCl is decreased after annealing compared to normal alloy.

Correlation between surface roughness parameters and contact stress of gear

2020 ◽  
pp. 135065012092866
Author(s):  
Yang Duo ◽  
Tang Jinyuan ◽  
Zhou Wei ◽  
Wen Yuqin
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Correlation Analysis ◽  
Maximum Shear Stress ◽  
Three Dimensional ◽  
Peak Height ◽  
Tooth Surface ◽  
Curvature Radius ◽  
Roughness Parameters ◽  
Surface Roughness Parameters

To reveal the relationship between rough tooth surface microstructure characteristics and contact performance, contact analysis is carried out based on the measured surface topography of the tooth surface of ultrasonic grinding by utilizing the elastic-plastic contact mechanics and statistical correlation analysis theory. Simple correlation analysis and partial correlation analysis are adopted for the gear three-dimensional surface roughness parameters and the maximum Mises stress and maximum shear stress. Then, the method of stepwise regression analysis and path analysis is used to construct the best fitting linear model of 3D roughness parameters and the maximum Mises stress and maximum shear stress, and the parameters’ decision coefficient is obtained. The research shows: (1) the rank of comprehensive influence factors of the maximum Mises stress is as follows: arithmetical mean height ( Sa), peak material portion ( Smr1), maximum peak height ( Sp), reduced peak height ( Spk), and minimum curvature radius and height ratio ( K), where Smr1, Spk, and K are negatively correlated with the maximum Mises stress; (2) the comprehensive influence variables of the maximum shear stress are in the order of Sa, Spk, and Vmp, among which Spk and Vmp are inversely related to the maximum shear stress.

scholarly journals Effect of Pressure Fluctuations and Flow Confinement on Shear Stress in Jet-Driven Scour Processes

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 718 ◽  
Author(s):  
Simone Pagliara ◽  
Michele Palermo
Keyword(s):  
Shear Stress ◽  
Maximum Shear Stress ◽  
Pressure Fluctuations ◽  
Flow Conditions ◽  
Effect Of Pressure ◽  
Black Water ◽  
Stress Coefficient ◽  
Average Shear ◽  
Confined Environment ◽  
Bed Material

The effect of pressure fluctuations and flow confinement on shear stress still represents a challenging problem for hydraulic engineers. Only a few studies investigated such aspects, but they did not focus on jet-driven scour processes in granular bed material. Following a recent theoretical framework, this paper presents a novel analytical procedure to assess the effect of pressure fluctuations on the average shear stress for 2D equilibrium configuration, under steady, black water flow conditions. The analysis of experimental data evidences that published formulas underestimate the maximum shear stress, because of the significant flow confinement and the presence of rotating material in the scour hole. Therefore, based on the hydrodynamic similitude characterizing the jet diffusion in a confined environment, a new shear stress coefficient and a novel equation are proposed to estimate the maximum shear stress for the tested configuration.

scholarly journals Effect of gamma radiation on creep behavior, hardness and microstructure of Titanium dental material

2017 ◽  
pp. 5078-5084
Author(s):  
A. El Bediwi ◽  
Eman Kashita ◽  
Salah. M .M.Salman
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Gamma Radiation ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Vickers Hardness ◽  
Maximum Shear Stress ◽  
Dental Material ◽  
Roughness Parameters ◽  
Matrix Microstructure

Effect of gamma radiation with fixed doses on creep behavior, Vickers hardness, maximum shear stress and surface roughness parameters of cp Titanium have been investigated.  Vickers hardness and maximum shear stress values of cp Titanium are decreased after irradiated at 10, 20 and 30 kGy.  Surface roughness Ra of cp Titanium varied after irradiated at 10, 20 and 30 kGy.  Stress exponent values of cp Titanium decreased after irradiated at 10, 20 and 30 kGy.  Matrix microstructure of cp Titanium changed (Intensity, broadness and position) after irradiated at 10, 20 and 30 kGy.

PEDOT:PSS Coating Improves Gecko-Inspired Adhesive Performance

2020 ◽  
Vol 8 (3) ◽  
Author(s):  
Capella Kerst ◽  
Srinivasan A. Suresh ◽  
Marc Ferro ◽  
Mark Cutkosky
Keyword(s):  
Shear Stress ◽  
Surface Treatment ◽  
Rough Surfaces ◽  
Maximum Shear Stress ◽  
Coating Process ◽  
Test Results ◽  
Polystyrene Sulfonate ◽  
Dry Adhesive ◽  
Normal Adhesion ◽  
Adhesive Performance

Abstract We report a surface treatment for an elastomeric dry adhesive that improves adhesion, especially on surfaces with microscopic roughness. The process involves coating wedge-shaped polydimethylsiloxane (PDMS) features of the adhesive with a 50 nm coating of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). As compared to the uncoated adhesive, performance is 1.25× better on smooth surfaces like glass, with a maximum shear stress of 70 kPa in shear and 25 kPa in normal adhesion under controlled loading conditions. On slightly rough surfaces such as paper and panels painted with flat paint, it provides between 2.5× and over 12× greater shear stress than the uncoated adhesive. Moreover, the coating, being much stiffer than the underlying wedges, does not increase the tendency to become dirty and does not tend to self-stick, or clump. Durability tests show that the performance remains substantially unchanged for 80,000 attachment/loading/detachment cycles. We describe the coating process, present the test results, and discuss the reasons for the enhanced performance on a variety of materials.

scholarly journals Studying the performance of fully encapsulated rock bolts with modified structural elements

2021 ◽  
Author(s):  
Jianhang Chen ◽  
Hongbao Zhao ◽  
Fulian He ◽  
Junwen Zhang ◽  
Kangming Tao
Keyword(s):  
Shear Stress ◽  
Load Transfer ◽  
Maximum Shear Stress ◽  
Coupling Model ◽  
Numerical Approach ◽  
Rock Bolt ◽  
Structural Elements ◽  
Rock Bolts ◽  
Two Stage ◽  
Bolt Diameter

AbstractNumerical simulation is a useful tool in investigating the loading performance of rock bolts. The cable structural elements (cableSELs) in FLAC3D are commonly adopted to simulate rock bolts to solve geotechnical issues. In this study, the bonding performance of the interface between the rock bolt and the grout material was simulated with a two-stage shearing coupling model. Furthermore, the FISH language was used to incorporate this two-stage shear coupling model into FLAC3D to modify the current cableSELs. Comparison was performed between numerical and experimental results to confirm that the numerical approach can properly simulate the loading performance of rock bolts. Based on the modified cableSELs, the influence of the bolt diameter on the performance of rock bolts and the shear stress propagation along the interface between the bolt and the grout were studied. The simulation results indicated that the load transfer capacity of rock bolts rose with the rock bolt diameter apparently. With the bolt diameter increasing, the performance of the rock bolting system was likely to change from the ductile behaviour to the brittle behaviour. Moreover, after the rock bolt was loaded, the position where the maximum shear stress occurred was variable. Specifically, with the continuous loading, it shifted from the rock bolt loaded end to the other end.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

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