The Elastic Contact of Rough Spheres

1967 ◽  
Vol 34 (1) ◽  
pp. 153-159 ◽  
Author(s):  
J. A. Greenwood ◽  
J. H. Tripp
Keyword(s):  
Pressure Distribution ◽  
Physical Contact ◽  
Contact Theory ◽  
Elastic Contact ◽  
Smooth Surfaces ◽  
Effective Pressure ◽  
Electric Contact

The Hertzian theory of elastic contact between spheres is extended by considering one of the spheres to be rough, so that contact occurs, as in practice, at a number of discrete microcontacts. It is found that the Hertzian results are valid at sufficiently high loads, but at lower loads the effective pressure distribution is much lower and extends much further than for smooth surfaces. The relevance to the physical-contact theory of friction and electric contact is considered.

A Compact Model for Spherical Rough Contacts

2005 ◽  
Vol 127 (4) ◽  
pp. 884-889 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Experimental Data ◽  
Pressure Distribution ◽  
Contact Pressure ◽  
Compact Model ◽  
Elastic Contact ◽  
Smooth Surfaces ◽  
New Model ◽  
Maximum Contact ◽  
Good Agreement ◽  
Key Parameter

A new model is developed that considers the effect of roughness on the elastic contact of spherical bodies. A general pressure distribution is proposed that encompasses the contact of rough spheres and yields the Hertzian theory for ideally smooth surfaces. A new parameter, nondimensional maximum contact pressure, is introduced and it is shown that this is the key parameter that controls the contact. The results of the present study are presented in the form of compact relationships. These relationships are compared against the experimental data collected by others and good agreement is observed.

Two-dimensional pressure field and backflow in the annular skirt of vortex gripper

2020 ◽  
pp. 095440622097404
Author(s):  
Jianghong Zhao ◽  
Xin Li
Keyword(s):  
Flow Field ◽  
Pressure Distribution ◽  
Local Stress ◽  
Vortex Chamber ◽  
Physical Contact ◽  
Two Dimensional ◽  
Stress Concentrations ◽  
Suction Force ◽  
Maximum Value ◽  
Gap Height

The vortex gripper is a kind of pneumatic noncontact gripper that does not produce a magnetic field and heat. It can grip a workpiece without physical contact, which avoids any unintentional damage such as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study focused on the two-dimensional pressure distribution field on a workpiece surface under the vortex gripper. Theoretical, experimental, and computational fluid dynamics results were combined to study the backflow phenomenon in the annular skirt, which can decrease the gripper’s suction force after the maximum value is reached. First, the pressure distribution in the annular skirt was theoretically modeled. A comparison with the experimental results showed that increasing the gap height between the gripper and workpiece generates a circumferentially asymmetrical flow field in the skirt. Based on this, it was hypothesized that an airflow in the circumferential direction may exist. The experimental data and simulation results were analyzed under large gap height conditions to observe the backflow in detail and it was found that an uneven pressure distribution with positive and negative pressure regions generated by the uneven flow is the root cause of the backflow. Finally, the effect of the backflow on the flow field in two different flow regions (in the annular skirt and inside the vortex chamber) was analyzed and the reason why the suction force of the vortex gripper has a maximum value was determined.

Effects of strain hardening and residual stress in impression on the instrumented indentation technique

2006 ◽  
Vol 21 (7) ◽  
pp. 1680-1686
Author(s):  
L.Z. Liu ◽  
Y.W. Bao ◽  
Y.C. Zhou
Keyword(s):  
Residual Stress ◽  
Strain Hardening ◽  
Energy Analysis ◽  
Maximum Load ◽  
Contact Theory ◽  
Elastic Contact ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Indentation Tests ◽  
Elastic Loading

Finite element analyses were carried out to simulate the loading, unloading, and reloading processes of indentation tests. It was found that the validity of applying the elastic contact theory to the indentation unloading process is strongly related to the strain hardening and residual stress in impression. It is the combination of strain hardening and residual stress that causes the unloading or reloading curves to show elastic loading in the range from zero to the maximum load whereas the reloading curve on the impression without strain hardening and residual stress shows elastic–plastic loading in the same range. These computations indicate that applying the elastic contact theory to the unloading or reloading processes, the fundamental prerequisite of the instrumented indentation technique, is valid because of the existence of strain hardening and residual stress. The mechanism of this hardening effect is discussed through energy analysis.

On the Applicability of Sneddon's Solution for Interpreting the Indentation of Nonlinear Elastic Biopolymers

2014 ◽  
Vol 81 (9) ◽  
Author(s):  
Man-Gong Zhang ◽  
Jinju Chen ◽  
Xi-Qiao Feng ◽  
Yanping Cao
Keyword(s):  
Elastic Properties ◽  
Viscoelastic Properties ◽  
Contact Theory ◽  
Elastic Contact ◽  
Flat Punch ◽  
Linear Elastic ◽  
Contact Models ◽  
Properties Of Materials ◽  
Nonlinear Elastic ◽  
Viscoelastic Contact

Indentation has been widely used to characterize the mechanical properties of biopolymers. Besides Hertzian solution, Sneddon's solution is frequently adopted to interpret the indentation data to deduce the elastic properties of biopolymers, e.g., elastic modulus. Sneddon's solution also forms the basis to develop viscoelastic contact models for determining the viscoelastic properties of materials from either conical or flat punch indentation responses. It is worth mentioning that the Sneddon's solution was originally proposed on the basis of linear elastic contact theory. However, in both conical and flat punch indentation of compliant materials, the indented solid may undergo finite deformation. In this case, the extent to which the Sneddon's solution is applicable so far has not been systematically investigated. In this paper, we use the combined theoretical, computational, and experimental efforts to investigate the indentation of hyperelastic compliant materials with a flat punch or a conical tip. The applicability of Sneddon's solutions is examined. Furthermore, we present new models to determine the elastic properties of nonlinear elastic biopolymers.

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.

Pressure Distribution between Closely Contacting Surfaces

1980 ◽  
Vol 22 (5) ◽  
pp. 251-259 ◽  
Author(s):  
A. Mostofi ◽  
R. Gohar
Keyword(s):  
Pressure Distribution ◽  
Contact Stress ◽  
Cylindrical Hole ◽  
Elastic Contact ◽  
Infinite Body ◽  
Reduced Pressure ◽  
Contact Arc ◽  
Two Bodies

The pressure distribution, contact arc extent, and deflection are determined for the elastic contact of a long roller and a cylindrical hole in an infinite body. It is shown that these variables depend on the degree of conformity of the two bodies and that Hertz's theory should not be used when the arc dimensions are of the same order as the radii of curvature, as its assumptions are violated. When the hole circumference available is reduced, pressure discontinuities can occur where the arc terminates. The results of the analysis have application in the design of some engineering components, such as complete and partial arc bearings and Novikov gears, where a knowledge of the magnitude and distribution of the contact stress is important.

scholarly journals Two cosine wave elastic-plastic contact model

2020 ◽  
Vol 103 (4) ◽  
pp. 003685042098061
Author(s):  
Tieneng Guo ◽  
Xu Hua ◽  
Lingjun Meng ◽  
Zhijie Yan ◽  
Liwei Peng
Keyword(s):  
Mechanical Model ◽  
Deformation Process ◽  
Mechanical Characteristics ◽  
Contact Theory ◽  
Elastic Contact ◽  
The Finite Element Method ◽  
Elastic Plastic ◽  
Mechanics Model ◽  
The Difference ◽  
The Relationship

Based on Hertz elastic contact theory, the contact mechanics model of two cosine wave is established. The mechanical characteristics of the model in the elastic, elastic-plastic, and plastic stages were studied. The influence of load on contact deformation and other characteristics is considered. The finite element method is used to analyze the deformation process of the model, and the results are compared with those of the mechanical model. The effects of amplitude and wavelength of cosine wave on its mechanical characteristics are discussed. The results show that the model reflects the relationship between the load and the mechanical characteristics of the model, and the difference of amplitude and wavelength will affect this characteristic.

scholarly journals Pressure distribution in tilting and reclining wheelchairs with an air cushion: A pilot study

2021 ◽  
Vol 13 (1) ◽  
pp. 121-127
Author(s):  
Hyunwoo Choi ◽  
Heymin Lee ◽  
Jeongwon Choi ◽  
Jisu Moon ◽  
Juhyang Jeong ◽  
...  
Keyword(s):  
College Students ◽  
Pilot Study ◽  
Pressure Distribution ◽  
Tilt Angle ◽  
Female College Students ◽  
Effective Pressure ◽  
Optimal Angle ◽  
Male And Female ◽  
Wheelchair Users ◽  
Air Cushion

Abstract Study aim: The aim of this study was to determine the optimal angle for maximizing pressure distribution in two types of wheelchairs (tilting and reclining) while using a ROHO cushion, which offers relatively effective pressure distribution. Material and methods: This study enrolled 28 male and female college students who understood the purpose of the study and agreed to participate. This study aimed to determine the optimal angle for tilting and reclining wheelchairs when using a ROHO cushion at angles of 10°, 20°, and 30° with tilted wheelchairs and 90°, 110°, and 130° with reclining wheelchairs. Results: The analysis showed that an improved pressure distribution when a tilting wheelchair was used versus a reclining one. A reclining position of ≥110° and a tilt angle of ≥20° led to significant pressure-reducing effects. Conclusion: The results of this study will help wheelchair users or their guardians to select the optimal wheelchair angle when changing their posture to prevent bedsores. Although no slippage was observed in our study, it is important to remember the proper back position to prevent unnecessary slippage.

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