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.

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 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.

Variable viscosity effects on third-grade liquid flow in post-treatment analysis of wire coating in the presence of nanoparticles

2018 ◽  
Vol 28 (10) ◽  
pp. 2423-2441 ◽  
Author(s):  
B. Mahanthesh ◽  
B.J. Gireesha ◽  
M. Archana ◽  
Tasawar Hayat ◽  
Ahmed Alsaedi
Keyword(s):  
Shear Stress ◽  
Numerical Solutions ◽  
Volume Fraction ◽  
Variable Viscosity ◽  
Post Treatment ◽  
Third Grade ◽  
Coating Process ◽  
Wire Surface ◽  
Content Type ◽  
Wire Coating

Purpose The features of coated wire product are measured by the flow and heat transport occurring in the interior of dies. Therefore, an understanding of characteristics of polymers momentum, heat mass transfer and wall shear stress is of great interest. Enhancement of heat transfer rate is fundamental need of wire coating process. Therefore, this study aims to investigate the effect of suspended nanoparticles in heat and mass transport phenomena of third-grade liquid in post-treatment of wire coating process. Buongiorno model for nanofluid is adopted. Two cases of temperature dependent viscosity are considered. Design/methodology/approach The governing equations are modelled with the help of steady-state conservation equations of mass, momentum, energy and nanoparticle concentration. Some appropriate dimensionless variables are introduced. Numerical solutions for the nonlinear problem are developed through Runge–Kutta–Fehlberg technique. The outcome of sundry variables for dimensionless flow, thermal and nanoparticle volume fraction fields are scrutinised through graphical illustrations. Findings The study’s numerical results disclose that the force on the total wire surface and shear stress at the surface in case of Reynolds Model dominate Vogel’s Model case. Impact of nanoparticles is constructive for force on the total wire surface and shear stress at the surface. The velocity of the coating material can be enhanced by the non-Newtonian property. Practical implications This study may provide useful information to improve the wire coating technology. Originality/value Effect of nanoparticles in wire coating analysis by using Brownian motion and thermophoresis slip mechanisms is investigated for the first time. Two different models for variable viscosity are used.

A critical look at the Wallace-Bott hypothesis in fault-slip analysis

2013 ◽  
Vol 184 (4-5) ◽  
pp. 299-306 ◽  
Author(s):  
Richard J. Lisle
Keyword(s):  
Shear Stress ◽  
Maximum Shear Stress ◽  
Fault Slip ◽  
Shear Stresses ◽  
Homogeneous State ◽  
Slip Direction ◽  
Fault Surface ◽  
State Of Stress ◽  
Simultaneous Movement

AbstractThe assumption is widely made that slip on faults occurs in the direction of maximum resolved shear stress, an assumption known as the Wallace-Bott hypothesis. This assumption is used to theoretically predict slip directions from known in situ stresses, and also as the basis of palaeostress inversion from fault-slip data. This paper examines different situations in relation to the appropriateness of this assumption. Firstly, it is shown that the magnitude of the shear stress resolved within a plane is a function with a poorly defined maximum direction, so that shear stress values greater than 90% of the maximum occur within a wide angular range (± 26°) degrees. The situation of simultaneous movement on pairs of faults requires slip on each fault to be parallel to their mutual line of intersection. However, the resolved shear stresses arising from a homogeneous state of stress do not accord with such a slip arrangement except in the case of pairs of perpendicular faults. Where fault surfaces are non-planar, the directions of resolved shear stress in general give, according to the Wallace-Bott hypothesis, a set of slip directions of rigid fault blocks, which is generally kinematically incompatible. Finally, a simple model of a corrugated fault suggests that any anisotropy of the shear strength of the fault such as that arising from fault surface topography, can lead to a significant angular difference between the directions of maximum shear stress and the slip direction.These findings have relevance to the design of procedures used to estimate palaeostresses and the amount of data required for this type of analysis.

Study on Thermal Cycling of Sn0.7Cu Solder

2013 ◽  
Vol 791-793 ◽  
pp. 362-365
Author(s):  
Li Yang ◽  
Ju Li Li ◽  
Jing Guo Ge ◽  
Meng Li ◽  
Nan Ji
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
High Temperature ◽  
Thermal Cycling ◽  
Shear Strain ◽  
Maximum Shear Stress ◽  
Steady State Creep ◽  
Maximum Shear Strain ◽  
Cycle Number ◽  
State Cycle

Thermal cycling of a unit Sn0.7Cu solder was studied based on the steady-state creep constitutive equation and Matlab software. The results show that there is a steady-state cycle for the thermal cycling of unit Sn0.7Cu eutectic solder. In steady-state thermal cycling, the shear stress is increased with the increase of temperature. There is a stage of stress relaxation during high temperature. A liner relationship between maximum shear stress and maximum shear strain is observed during thermal cycling. The metastable cycle number is declined greatly with the increase of maximum shear strain.

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 Numerical Study of Fluid Dynamics in Suspension Culture of iPS Cells

2019 ◽  
Vol 17 (1) ◽  
pp. 73 ◽  
Author(s):  
Masaki Yano ◽  
Takuya Yamamoto ◽  
Yasunori Okano ◽  
Toshiyuki Kanamori ◽  
Mashiro Kino–oka
Keyword(s):  
Shear Stress ◽  
Suspension Culture ◽  
Numerical Study ◽  
Maximum Shear Stress ◽  
Ips Cells ◽  
Stirred Tanks ◽  
Average Shear Stress ◽  
Average Shear ◽  
Orbital Shaking ◽  
Induced Pluripotent

In a suspension culture of iPS cells, the shear stress generated during mixing is expected to promote differentiation of induced pluripotent stem (iPS) cells. The stress on the cells can be controlled by rotational rate and shape of impeller. However, it is difficult to optimize these operative parameters by experiments. Therefore, we have developed a numerical model to obtain the average and the maximum shear stress in two kinds of stirred tanks and an orbital shaking cylindrical container. The present results showed that the shear stress strongly depended on the type of mixing and lesser extent on the shape of the impeller. The average shear stress is larger in the shaking mode than that in the stirring mode. In contrast, the maximum shear stress is much smaller in the shaking than the stirring. These results suggest that stirring and shaking should be selectively used depending on the application

Sign in / Sign up

Export Citation Format

Share Document