An Asperity Microcontact Model Incorporating the Transition From Elastic Deformation to Fully Plastic Flow

1999 ◽  
Vol 122 (1) ◽  
pp. 86-93 ◽  
Author(s):  
Yongwu Zhao ◽  
David M. Maietta ◽  
L. Chang
Keyword(s):  
Plastic Flow ◽  
Elastic Deformation ◽  
Rough Surfaces ◽  
Plasticity Index ◽  
Contact Load ◽  
Elastic Plastic ◽  
Surface Separation ◽  
Surface Plasticity ◽  
Wide Range ◽  
The Mean

This paper presents an elastic-plastic asperity microcontact model for contact between two nominally flat surfaces. The transition from elastic deformation to fully plastic flow of the contacting asperity is modeled based on contact-mechanics theories in conjunction with the continuity and smoothness of variables across different modes of deformation. The relations of the mean contact pressure and contact area of the asperity to its contact interference in the elastoplastic regime of deformation are respectively modeled by logarithmic and fourth-order polynomial functions. These asperity-scale equations are then used to develop the elastic-plastic contact model between two rough surfaces, allowing the mean surface separation and the real area of contact to be calculated as functions of the contact load and surface plasticity index. Results are presented for a wide range of contact load and plasticity index, showing the importance of accurately modeling the deformation in the elastoplastic transitional regime of the asperity contacts. The results are also compared with those calculated by the GW and CEB models, showing that the present model is more complete in describing the contact of rough surfaces. [S0742-4787(00)01201-7]

A Model of Asperity Interactions in Elastic-Plastic Contact of Rough Surfaces

2000 ◽  
Vol 123 (4) ◽  
pp. 857-864 ◽  
Author(s):  
Yongwu Zhao ◽  
L. Chang
Keyword(s):  
Plastic Deformation ◽  
Rough Surfaces ◽  
Local Deformation ◽  
Contact Model ◽  
Contact Load ◽  
Elastic Plastic ◽  
Surface Separation ◽  
Local Contact ◽  
Mean Pressure ◽  
The Mean

This paper presents a micro-contact model incorporating asperity interactions in elastic-plastic contact of rough surfaces. The effect of the asperity interactions on the local deformation behavior of a given micro-contact is first modeled based on the Saint-Venant’s Principle and Love’s Formula. The local contact interference is related in closed form to the local contact load, the global mean pressure and material parameters. This micro-contact model equation is then integrated into the elastic-plastic contact model developed in Zhao et al. (2000) to allow the asperity interactions and plastic deformation to be considered simultaneously. The effects of the asperity interactions on the mean surface separation, the real area of contact and the redistribution of the contact load among contacting asperities of different heights are studied. The results show that the asperity interactions can significantly affect the mean surface separation and micro-contact load redistribution. The results also reveal that the effect of asperity interactions can be largely cancelled out by the effect of asperity plastic deformation.

Strongly Anisotropic Rough Surfaces

1979 ◽  
Vol 101 (1) ◽  
pp. 15-20 ◽  
Author(s):  
A. W. Bush ◽  
R. D. Gibson ◽  
G. P. Keogh
Keyword(s):  
Random Process ◽  
Rough Surface ◽  
Contact Area ◽  
Process Model ◽  
Rough Surfaces ◽  
Plasticity Index ◽  
Real Contact Area ◽  
Elastic Contact ◽  
Elastic Plastic ◽  
Real Contact

The statistics of a strongly anisotropic rough surface are briefly described. The elastic contact of rough surfaces is treated by approximating the summits of a random process model by parabolic ellipsoids and applying the Hertzian solution for their deformation. Load and real contact area are derived as functions of the separation and for all separations the load is found to be approximately proportional to the contact area. The limits of elastic/plastic contact are discussed in terms of the plasticity index.

Elastic-Plastic Contact Behavior Considering Asperity Interactions for Surfaces With Various Height Distributions

2005 ◽  
Vol 128 (2) ◽  
pp. 245-251 ◽  
Author(s):  
Yeau-Ren Jeng ◽  
Shin-Rung Peng
Keyword(s):  
Contact Area ◽  
Rough Surfaces ◽  
Local Deformation ◽  
Real Contact Area ◽  
Recent Experimental Data ◽  
The Real ◽  
Surface Separation ◽  
Real Contact ◽  
The Mean ◽  
Non Gaussian

This study investigates the effects of asperity interactions on the mean surface separation and the real contact area for rough surfaces with non-Gaussian height distributions. The effects of the asperity interactions on the local deformation behavior of a given microcontact are modeled using the Saint Venant principle and Love’s formula. The non-Gaussian rough surfaces are described by the Johnson translatory system. The results indicate that asperity interactions can significantly affect the mean separation of surfaces with non-Gaussian height distributions. The findings also reveal that the contact load and the real contact area of surfaces with non-Gaussian height distributions are significantly different from those of surfaces with Gaussian height distributions. This study uncovers that skewed surfaces tend to deform more elastically, which provides underlying physics for the long-time conventional wisdom and recent experimental data [Y. R. Jeng, 1996, Tribol. Trans., 39, 354–361;Y. R. Jeng, Z. W. Lin, and S. H. Shyo, 2004, ASME J. Tribol., 126, 620–625] that running-in surfaces have better wear resistance.

A Rate-Dependent Inelastic Constitutive Model—Part I: Elastic-Plastic Flow

1991 ◽  
Vol 113 (3) ◽  
pp. 314-323 ◽  
Author(s):  
F. Ellyin ◽  
Z. Xia
Keyword(s):  
Constitutive Model ◽  
Plastic Flow ◽  
Inelastic Deformation ◽  
Experimental Results ◽  
Elastic Plastic ◽  
Rate Dependent ◽  
Wide Range ◽  
Strain Stress ◽  
Standard Tests ◽  
Inelastic Processes

In this part a rate-dependent elastic-plastic constitutive model is presented which is an extension of our earlier rate-indpendent model. The effect of prior creep on the subsequent inelastic deformation is also included. The model can be used to predict inelastic processes with variable strain (stress) rates. It is shown, through comparison with the experimental results, that most of the rate-effect features of the material response can be simulated by the model. Despite the wide range of application, the model is relatively simple and incorporated a few material constants which could be easily determined from standard tests.

A Static Friction Model for Elastic-Plastic Contacting Rough Surfaces

2004 ◽  
Vol 126 (1) ◽  
pp. 34-40 ◽  
Author(s):  
Lior Kogut ◽  
Izhak Etsion
Keyword(s):  
Friction Coefficient ◽  
Rough Surfaces ◽  
Static Friction ◽  
Friction Model ◽  
Plasticity Index ◽  
High Plasticity ◽  
Elastic Plastic ◽  
Static Friction Coefficient ◽  
Contact Adhesion ◽  
Limiting Case

A model that predicts the static friction for elastic-plastic contact of rough surfaces is presented. The model incorporates the results of accurate finite element analyses for the elastic-plastic contact, adhesion and sliding inception of a single asperity in a statistical representation of surface roughness. The model shows strong effect of the external force and nominal contact area on the static friction coefficient in contrast to the classical laws of friction. It also shows that the main dimensionless parameters affecting the static friction coefficient are the plasticity index and adhesion parameter. The effect of adhesion on the static friction is discussed and found to be negligible at plasticity index values larger than 2. It is shown that the classical laws of friction are a limiting case of the present more general solution and are adequate only for high plasticity index and negligible adhesion. Some potential limitations of the present model are also discussed pointing to possible improvements. A comparison of the present results with those obtained from an approximate CEB friction model shows substantial differences, with the latter severely underestimating the static friction coefficient.

Model for Elastic–Plastic Contact Between Rough Surfaces

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Zhiqian Wang ◽  
Xingna Liu
Keyword(s):  
Rough Surfaces ◽  
Plasticity Index ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Single Asperity ◽  
Deformation Regime ◽  
Smooth Model ◽  
Relationship Of ◽  
The Relationship ◽  
Contact Displacement

This paper studies elastic–plastic contact between Greenwood–Williamson (GW) rough surfaces, on which there are many asperities with the same radius whose height obeys the Gaussian distribution. A new plasticity index is defined as the ratio of the standard deviation of the height of asperities on the rough surface to the single-asperity critical displacement (the transition point from the elastic to the elastic-fully plastic deformation regime), which is linearly proportional to the GW plasticity index to the power of 2. The equations for the load/area–separation relationship of rough surfaces are presented based on Wang and Wang's smooth model of singe-asperity elastic–plastic contact, which is an improvement of the Kogut–Etsion (KE) empirical model based on finite element analysis (FEA) data. The load/area–separation relationship can be described by empirical Gaussian functions. The load–area relationship of rough surfaces is approximately linear. The average pressure is only function of the new plasticity index. According to Wang and Wang's conclusion that Etsion et al. single-asperity elastic–plastic loading (EPL) index is approximately equal to the ratio of the single-asperity residual plastic contact displacement to the single-asperity total elastic–plastic contact displacement, the equations for the relationship between Kadin et al. modified plasticity index (MPI) and separation of rough surfaces are also presented. In addition, the MPI is approximately linearly proportional to the separation between rough surfaces for a given new plasticity index ranging from 5 to 30. When the new plasticity index is smaller than 5, due to the large proportion of the elastic deformation in the total deformation, the MPI slightly deviate from linearity.

Magnetomechanical Instabilities in Elastic-Plastic Cylinders, Part II: Plastic Response

1996 ◽  
Vol 63 (3) ◽  
pp. 742-749 ◽  
Author(s):  
D. L. Littlefield
Keyword(s):  
Electric Current ◽  
Plastic Flow ◽  
Plastic Material ◽  
Yield Criterion ◽  
Confining Pressure ◽  
Constitutive Law ◽  
Linear Perturbation ◽  
Uniform Motion ◽  
Elastic Plastic ◽  
Wide Range

The analysis of elastic instabilities in metal cylinders when subjected to electromagnetic fields (Littlefield, 1996a) is extended in this work to include elastic-plastic flow. The cylinder is assumed to be infinitely long and perfectly conducting. The Prandtl-Reuss elastic-plastic material model is the assumed constitutive law, with the von Mises yield criterion employed to limit the effective stress. An axial electric current, assumed to be conducting along the surface of the cylinder, generates a confining pressure, causing plastic flow that is initially assumed to be uniform throughout the cross section. The propagation of small axisymmetric disturbances to this uniform motion is studied by applying linear perturbation theory. Solutions to these equations exhibit a wide range of instability modes, as was the case for the purely elastic results, and the frequency of the oscillating disturbances appears to be suppressed by electromagnetic effects. However, in contrast to the elastic result, no threshold magnetic field exists, and distending instabilities are possible for all levels of electric current. Physical mechanisms resulting in these distinctions are suggested.

An Elliptic Elastic-Plastic Asperity Microcontact Model for Rough Surfaces

1998 ◽  
Vol 120 (1) ◽  
pp. 82-88 ◽  
Author(s):  
Jeng Haur Horng
Keyword(s):  
Present Model ◽  
Rough Surfaces ◽  
Plasticity Index ◽  
Contact Model ◽  
Real Contact Area ◽  
Elastic Plastic ◽  
Surface Topographies ◽  
Elliptic Contact ◽  
Contact Spots ◽  
Circular Contact

An elastic-plastic microcontact model, that takes into account the directional nature of surface roughness, is proposed for elliptic contact spots between anisotropic rough surfaces. In addition, the plasticity index was modified to suit more general geometric contact shapes. This contact model, which expands the usefulness of the CEB model, is also utilized to determine the effect of effective radius ratio (γ) on microcontact behavior and to compare the results of this model and other models under different surface topographies. The results show that the elliptic contact model and circular contact model deviate considerably in regard to the separation (h), total real contact area (At), plastic area (Ap) and plasticity index (Ψ). The present model can be simplified to become other stochastic models.

Elastic-Plastic Adhesive Contact of Rough Surfaces Based on Accurate FEA Study Using N-Point Asperity Model

2014 ◽  
Vol 2 (2) ◽  
pp. 1-22
Author(s):  
Ajay K. Waghmare ◽  
Prasanta Sahoo
Keyword(s):  
Plastic Deformation ◽  
Rough Surfaces ◽  
Adhesive Contact ◽  
Plasticity Index ◽  
Asperity Contact ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Significant Difference ◽  
Asperity Model ◽  
Adhesion Index

The paper describes a theoretical study of elastic-plastic adhesive contact of rough surfaces based on n-point asperity model and accurate finite element analysis (FEA) of elastic-plastic deformation of single asperity contact. The n-point asperity model developed by Hariri et al (2006) is integrated with the elastic-plastic model of . In this study an attempt is made to extend the work of by incorporating intermediate elastic-plastic regime of deformation. A large range of interference values ranging from fully elastic through elastic-plastic to fully plastic deformation of contacting asperities is considered. The effect of varying load and material parameters is analyzed in terms of well established adhesion index and plasticity index. A comparison between the present analysis with that of model shows significant difference in load–separation behaviour depending on combinations of mean separation, adhesion index and plasticity index.

A Comparison of Physiological Demand between Self-Propelled and Motorized Treadmill Exercise

2018 ◽  
Vol 7 (4) ◽  
pp. 13-21
Author(s):  
Todd Backes ◽  
Charlene Takacs
Keyword(s):  
Respiratory Exchange Ratio ◽  
Treadmill Exercise ◽  
Cardiopulmonary Exercise Testing ◽  
Mean Value ◽  
The Self ◽  
Mixing Chamber ◽  
Wide Range ◽  
The Subject ◽  
The Mean ◽  
Computer Controlled

There are a wide range of options for individuals to choose from in order to engage in aerobic exercise; from outdoor running to computer controlled and self-propelled treadmills. Recently, self-propelled treadmills have increased in popularity and provide an alternative to a motorized treadmill. Twenty subjects (10 men, 10 women) ranging in age from 19-23 with a mean of 20.4 ± 0.8 SD were participants in this study. The subjects visited the laboratory on three occasions. The purpose of the first visit was to familiarize the subject with the self-propelled treadmill (Woodway Curve 3.0). The second visit, subjects were instructed to run on the self-propelled treadmill for 3km at a self-determined pace. Speed data were collected directly from the self-propelled treadmill. The third visit used speed data collected during the self-propelled treadmill run to create an identically paced 3km run for the subjects to perform on a motorized treadmill (COSMED T150). During both the second and third visit, oxygen consumption (VO2) and respiratory exchange ratio (R) data were collected with COSMED’s Quark cardiopulmonary exercise testing (CPET) metabolic mixing chamber system. The VO2 mean value for the self-propelled treadmill (44.90 ± 1.65 SE ml/kg/min) was significantly greater than the motorized treadmill (34.38 ± 1.39 SE ml/kg/min). The mean R value for the self-propelled treadmill (0.91 ± 0.01 SE) was significantly greater than the motorized treadmill (0.86 ± 0.01 SE). Our study demonstrated that a 3km run on a self-propelled treadmill does elicit a greater physiological response than a 3km run at on a standard motorized treadmill. Self-propelled treadmills provide a mode of exercise that offers increased training loads and should be considered as an alternative to motorized treadmills.

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