scholarly journals Intersurface Adhesion in the Presence of Capillary Condensation

2018 ◽  
Vol 85 (6) ◽  
Author(s):  
Jianfeng Sun ◽  
Sinan Müftü ◽  
April Z. Gu ◽  
Kai-Tak Wan
Keyword(s):  
Capillary Condensation ◽  
Finite Size ◽  
Force Balance ◽  
Contact Theory ◽  
Contact Radius ◽  
Water Molecules ◽  
Hertz Contact ◽  
Rigid Substrate ◽  
Approach Distance ◽  
Classical Models

An elastic sphere adheres to a rigid substrate in the presence of moisture. The adhesion–detachment trajectory is derived based on the Hertz contact theory that governs the contact mechanics and Laplace–Kelvin equation that governs the water meniscus at the interface. The intersurface attraction is solely provided by the Laplace pressure within the meniscus. Interrelation between the applied load, contact radius, and approach distance is derived based on a force balance. The resulting “pulloff” force to detach the sphere exceeds the critical load in the Derjaguin–Muller–Toporov (DMT) limit which only holds at saturated moisture. The new model accounts for the finite size of water molecules that is missing in virtually all classical models.

Effect of Body Lateral Extension Upon the Elastic Contact

2009 ◽  
Author(s):  
Marilena Glovnea ◽  
Emanuel Diaconescu
Keyword(s):  
Half Space ◽  
Outer Radius ◽  
Force Balance ◽  
Contact Theory ◽  
Contact Radius ◽  
Elastic Contact ◽  
Space Theory ◽  
Lateral Extension ◽  
Load Direction ◽  
Force Balance Equation

Half-space contact theory cannot be applied when either contacting bodies are thin or they possess small transversal dimensions. The former situation is often dealt with, but the latter seems to be neglected. This paper investigates the effect of outer radius of cylindrical bodies upon the contact stress field. The method consists in adding supplementary displacements and stresses to the half-space solution in order to fulfill the boundary conditions and the force balance equation on load direction. It is found that the half-space theory is applicable if transversal radius exceeds contact radius.

scholarly journals Investigation on indentation rolling resistance of belt conveyor based on Hertz contact theory compared with one-dimensional Winkler foundation

2018 ◽  
Vol 10 (7) ◽  
pp. 168781401878393 ◽  
Author(s):  
Lu Yan
Keyword(s):  
Rolling Resistance ◽  
Contact Theory ◽  
Theoretical Formula ◽  
Winkler Foundation ◽  
Hertz Contact ◽  
Belt Conveyor ◽  
One Dimensional ◽  
Hertz Contact Theory ◽  
Viscoelastic Theory ◽  
Indentation Rolling Resistance

Based on Hertz contact theory and one-dimensional Winkler foundation combination with viscoelastic theory, the author derived theoretical formulas of indentation rolling resistance, respectively. Using the laboratorial apparatus of indentation rolling resistance, the author mainly concentrates on the error analysis about two kinds of theoretical formula which bear on indentation rolling resistance compared with experimental result. The reason why author employs Hertz contact theory to discuss indentation rolling resistance is that indentation rolling resistance is a sort of contact resistance. As a result, Hertz contact theory is generally applicable to study it. On the other hand, because conveyor belt has viscoelastic property, it is appropriate to use viscoelastic theory by the aid of three-parameter Maxwell viscoelastic model combination with one-dimensional Winkler foundation. Ultimately, this article infers that theoretical formula based on the Hertz contact is brief and clear compared with one-dimensional Winkler foundation in principle. However, it is noticeable that when the belt is at high speed, the reliability of formula based on Hertz theory has decreased obviously. This conclusion can give a beneficial reference for the energy saving of belt conveyor.

Virtual Material Model of Joint Interfaces Considering Elastic-Plastic Deformation of Asperities

2013 ◽  
Vol 457-458 ◽  
pp. 257-261
Author(s):  
Li Gang Cai ◽  
Teng Yun Xu ◽  
Yong Sheng Zhao
Keyword(s):  
Plastic Deformation ◽  
Elastic Modulus ◽  
Fractal Theory ◽  
Material Model ◽  
Contact Theory ◽  
Hertz Contact ◽  
Calculation Methods ◽  
Elastic Plastic ◽  
Element Simulation ◽  
Simulation Results

A virtual material model of joint interfaces was established based on the Hertz contact theory and fractal theory, this model was improved by considering the influence of the elastic-plastic deformation of asperities and ameliorating the calculation methods of the elastic modulus. The simulation results of elastic-plastic considered and elastic-plastic unconsidered were compared, moreover, the finite element simulation results and experimental results were compared to fully explain the necessity of considering the influence of the elastic-plastic deformation and the the correctness of the method to calculate the elastic modulus. The research suggested that under a same load the elastic modulus of the model considering the influence of the elastic-plastic deformation was slightly larger than the un considering one, which means it could describe the characteristics of joint interfaces more accurately.

scholarly journals Экспериментальное и теоретическое исследование осциллятора с соударениями

2020 ◽  
Vol 90 (10) ◽  
pp. 1672
Author(s):  
В.В. Нарожнов
Keyword(s):  
Theoretical Model ◽  
Equations Of Motion ◽  
Spectral Characteristics ◽  
Contact Theory ◽  
Hertz Contact ◽  
Mechanical Oscillator ◽  
Impact Oscillator ◽  
Fourier Filtering ◽  
Nonlinear Mechanical ◽  
The Impact

The results of a study of a nonlinear mechanical oscillator with elastic impacts are presented. The experiment was carried out using an electromechanical impact oscillator. The theoretical model is based on the equations of motion, taking into account the elastic force, which is calculated under the Hertz contact theory. It is shown that bifurcations and attractors of the “stable focus” and “limit cycle” types can occur for the impact oscillator. Fourier filtering was used to analyze the spectral characteristics of the signals.

Seismic velocities and Poisson’s ratio of shallow unconsolidated sands

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 559-564 ◽  
Author(s):  
Ran Bachrach ◽  
Jack Dvorkin ◽  
Amos M. Nur
Keyword(s):  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Tangential Component ◽  
Poisson's Ratio ◽  
Contact Theory ◽  
Beach Sand ◽  
Contact Radius ◽  
Seismic Velocities ◽  
S Wave ◽  
Unconsolidated Sands

We determined P- and S-wave velocity depth profiles in shallow, unconsolidated beach sand by analyzing three‐component surface seismic data. P- and S-wave velocity profiles were calculated from traveltime measurements of vertical and tangential component seismograms, respectively. The results reveal two discrepancies between theory and data. Whereas both velocities were found to be proportional to the pressure raised to the power of 1/6, as predicted by the Hertz‐Mindlin contact theory, the actual values of the velocities are less than half of those calculated from this theory. We attribute this discrepancy to the angularity of the sand grains. Assuming that the average radii of curvature at the grain contacts are smaller than the average radii of the grains, we modify the Hertz‐Mindlin theory accordingly. We found that the ratio of the contact radius to the grain radius is about 0.086. The second disparity is between the observed Poisson’s ratio of 0.15 and the theoretical value (0.008 for random pack of quartz spheres). This discrepancy can be reconciled by assuming slip at the grain contacts. Because slip decreases the shearing between grains, Poisson’s ratio increases.

scholarly journals Compliant contact force models in multibody dynamics: Evolution of the Hertz contact theory

2012 ◽  
Vol 53 ◽  
pp. 99-121 ◽  
Author(s):  
Margarida Machado ◽  
Pedro Moreira ◽  
Paulo Flores ◽  
Hamid M. Lankarani
Keyword(s):  
Multibody Dynamics ◽  
Contact Force ◽  
Contact Theory ◽  
Hertz Contact ◽  
Hertz Contact Theory

Modeling of the coupled dynamics of damping particles filled in the cells of a honeycomb sandwich plate and experimental validation

2019 ◽  
Vol 25 (11) ◽  
pp. 1706-1719 ◽  
Author(s):  
Nazeer Ahmad ◽  
R. Ranganath ◽  
Ashitava Ghosal
Keyword(s):  
Coulomb Friction ◽  
Sandwich Plate ◽  
Experimental Studies ◽  
Contact Theory ◽  
Sandwich Composite ◽  
Hertz Contact ◽  
Damping Characteristics ◽  
Honeycomb Sandwich ◽  
High Level ◽  
Dem Model

Equipment panels of a spacecraft are made up of a sandwich composite with aluminum face sheets and a honeycomb (HC) core. The HC sandwich plate responds to the launch vibration loads subjecting the equipment mounted on it to a high level of accelerations at resonances owing to a lower natural damping. Damping particles (DPs) when inserted in the empty cells of a HC core improve the damping characteristics and reduce the resonance responses. In this work, we present a mathematical model governing the motion of the cell walls, DPs and HC plate under dynamic loading. The discrete element method (DEM) has been used to model the dynamics of the DPs wherein the contacts are modeled using modified nonlinear dissipative Hertz contact theory in conjunction with Coulomb friction. The effect of DPs on the responses at resonances, damping, and frequency response function (FRF) of the HC plate is obtained. Numerical and experimental studies were conducted on a HC plate where a selected portion of the plate was filled with DPs. The HC plate was subjected to sine sweep base acceleration at the edges to study the effect of DPs on the dynamic characteristic of the plate. The damping ratios and resonance peaks of the lower four modes of the HC plate, excited up to 1000 Hz, obtained experimentally from the FRF measurements and numerically from the DEM model compare well. The damping ratios, response at resonances and the FRF profiles are also similar. Significant improvement in damping ratios and attenuation of vibration level has been observed.

Plastic Yield Conditions for Adhesive Contacts

2008 ◽  
Author(s):  
Yu-Chiao Wu ◽  
George G. Adams
Keyword(s):  
Applied Load ◽  
Contact Theory ◽  
Hertz Contact ◽  
Hertz Theory ◽  
Yield Load ◽  
Plastic Yield ◽  
Curve Fit ◽  
Axis Of Symmetry ◽  
Adhesive Contacts ◽  
Yield Conditions

The Hertz contact theory allows the onset of yielding to be predicted for those contacts in which the effect of adhesion can be neglected. However in microscale contacts, such as those which occur in MEMS, yielding will occur for lower loads than predicted by the Hertz theory. For such cases, the JKR, DMT, and Greenwood-Johnson theories extend the Hertz theory to include the effect of adhesion. The present study provides yield conditions for the JKR, DMT, and Greenwood-Johnson theories of adhesion. Attention is first focused on the initiation of yield along the axis of symmetry of the contact. The results show that the critical loads for the three adhesion theories are close together, but differ significantly from that predicted by Hertz. In fact it is possible for yielding to occur due to adhesion alone, without an external applied load. A curve-fit formula is given to express the yield load as a function of an adhesion parameter for different Poisson’s ratios. Results are also obtained for the onset of plastic deformation away from the axis of symmetry using the Greenwood-Johnson theory of adhesion.

Analysis of Contact Stress on Coating Based upon Hertz Theory

2012 ◽  
Vol 155-156 ◽  
pp. 133-137
Author(s):  
Li Ping Wang ◽  
Hao Dong Luo ◽  
Yan Mei Cui
Keyword(s):  
Finite Element Method ◽  
Coating Thickness ◽  
Contact Stresses ◽  
Contact Theory ◽  
Hard Coating ◽  
Thin Coating ◽  
The Finite Element Method ◽  
Hertz Contact ◽  
Hertz Theory ◽  
Mechanics Performance

It is necessary to study the mechanics performance of thin coating, which composite the prerequisite of coating’s application. The contact stresses are important factors for the design of hard coating/substrate because the failure of the hard coating is usually caused by these stresses. The finite element method is applied to simulate the stress of coating with contact load based on Hertz contact theory. The accuracy of model was initially tested in systems without a film. The contact stresses have been calculated based on various coating/substrate modulus ratios and the coating thickness. Results show that coating thickness changes from 1.5um to 3um, the effects of coating/substrate combination is perfect. The research has important guiding significance for the application of coating.

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