Creep Relaxation of an Elastic–Perfectly Plastic Hemisphere in Fully Plastic Contact

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Andreas Goedecke ◽  
Randolf Mock
Keyword(s):  
Creep Behavior ◽  
Contact Area ◽  
Geometrical Parameters ◽  
Second Phase ◽  
Perfectly Plastic ◽  
Area Increase ◽  
Accelerated Creep ◽  
Material Creep ◽  
Evolution Laws ◽  
Elastic Perfectly Plastic

A set of finite element simulations was performed to analyze the creep behavior of an elastic–perfectly plastic hemisphere in contact with a rigid flat. This study focuses on the time-dependent stress relaxation of a fully plastic asperity. Assuming a Garofalo (hyperbolic sine) type material creep law, the asperity shows two distinct phases of relaxation. In the first phase, the asperity creeps with an accelerated creep rate and shows a contact area increase similar to that of a cylindrical geometry. In the second phase, no contact area change can be measured and the asperity creeps with a slower rate. Empirical evolution laws for the asperity creep behavior are presented, analyzing the influence of both material and geometrical parameters. The results are interpreted in terms of transient friction.

A Finite Element Based Study on the Elastic-Plastic Transition Behavior in a Hemisphere in Contact With a Rigid Flat

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
S. Shankar ◽  
M. M. Mayuram
Keyword(s):  
Finite Element ◽  
Contact Area ◽  
Plastic Material ◽  
Plastic Region ◽  
Real Contact Area ◽  
Real Contact ◽  
Perfectly Plastic ◽  
The Difference ◽  
Elastic Perfectly Plastic ◽  
Green Model

An axisymmetrical hemispherical asperity in contact with a rigid flat is modeled for an elastic perfectly plastic material. The present analysis extends the work (sphere in contact with a flat plate) of Kogut–Etsion Model and Jackson–Green Model and addresses some aspects uncovered in the above models. This paper shows the critical values in the dimensionless interference ratios (ω∕ωc) for the evolution of the elastic core and the plastic region within the asperity for different Y∕E ratios. The present analysis also covers higher interference ratios, and the results are applied to show the difference in the calculation of real contact area for the entire surface with other existing models. The statistical model developed to calculate the real contact area and the contact load for the entire surfaces based on the finite element method (FEM) single asperity model with the elastic perfectly plastic assumption depends on the Y∕E ratio of the material.

Junction Growth and Energy Dissipation at the Very Early Stage of Elastic-Plastic Spherical Contact Fretting

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Ovcharenko ◽  
I. Etsion
Keyword(s):  
Energy Dissipation ◽  
Friction Force ◽  
Contact Area ◽  
Early Stage ◽  
Static Friction ◽  
Relative Displacement ◽  
Elastic Plastic ◽  
Perfectly Plastic ◽  
Direct Measurements ◽  
Elastic Perfectly Plastic

The contact area, friction force, and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial junction growth and energy dissipation mainly in the first loading cycle. The so-called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly-plastic copper spheres.

Very Early Stage of Elastic-Plastic Spherical Contact Fretting

2009 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Izhak Etsion
Keyword(s):  
Friction Force ◽  
Contact Area ◽  
Early Stage ◽  
Static Friction ◽  
Relative Displacement ◽  
Elastic Plastic ◽  
Perfectly Plastic ◽  
Direct Measurements ◽  
Elastic Perfectly Plastic

The contact area, friction force and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial junction growth and energy dissipation mainly in the first loading cycle. The so called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly plastic copper spheres.

Static and dynamic effective moduli of elastic-perfectly plastic granular aggregates under normal compression

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. MR185-MR194 ◽  
Author(s):  
Abdulla Kerimov ◽  
Gary Mavko ◽  
Tapan Mukerji ◽  
Jack Dvorkin
Keyword(s):  
Contact Area ◽  
Spherical Particles ◽  
Effective Moduli ◽  
Normal Loading ◽  
Normal Contact ◽  
Elastic Case ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Unloading Stiffness ◽  
Explicit Expressions

Based on an existing simplified theoretical model for the normal contact interaction between two elastic-perfectly plastic spherical particles, we derived explicit expressions for the static and dynamic normal and dynamic tangential contact stiffnesses of elastic-perfectly plastic two-particle combination at pre-yield, yield, and post-yield conditions of normal loading. We used “static stiffness” or “loading stiffness” to refer to the slope of the force-displacement curve during monotonically increasing load. The “dynamic stiffness” or “unloading stiffness” refers to the stiffness that controls the speed of infinitesimal strain elastic waves propagating through the contacts. The static and dynamic contact stiffnesses are compared with numerical modeling of a two-sphere combination using the finite-element method. Furthermore, we used the explicit expressions for contact stiffnesses with the commonly used statistical averaging scheme to derive the static and dynamic effective bulk and shear moduli of a dry, random packing of identical elastic-perfectly plastic spherical particles. Elastic contact/mechanics-based effective medium models are unable to model the growth of contact area between inelastic (e.g., plastic) particles under normal force, which results in inaccurate predictions of contact stiffnesses and effective moduli. Once the particle reaches the limit of elasticity with onset of plastic deformation (yielding), further loading of two elastic-perfectly plastic spherical particles leads to a larger contact area than for two elastic particles under the same normal loading. As a result, after yielding, the dynamic effective moduli become stiffer than the corresponding moduli in the elastic case, whereas the static effective moduli remain constant, rather than increasing as in the elastic case.

scholarly journals Elastic-Perfectly Plastic Contact of Rough Surfaces: An Incremental Equivalent Circular Model

2021 ◽  
Author(s):  
GF WANG
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Yield Stress ◽  
Contact Area ◽  
Present Model ◽  
Rough Surfaces ◽  
Perfectly Plastic ◽  
Circular Model ◽  
Linear Load ◽  
Elastic Perfectly Plastic

In this paper, an incremental eqivalent contact model is developed for elastic-perfectly plastic solids with rough surfaces. The contact of rough surface is modeled by the accumulation of circular contacts with varying radius, which is estimated from the geometrical contact area and the number of contact patches. For three typical rough surfaces with various mechanical properties, the present model gives accurate predictions of the load-area relation, which are verified by direct finite element simulations. An approximately linear load-area relation is observed for elastic-plastic contact up to a large contact fraction of 15%, and the influence of yield stress is addressed.

Elastic-Perfectly Plastic Contact of Rough Surfaces: An Incremental Equivalent Circular Model

2021 ◽  
pp. 1-19
Author(s):  
Xuan-Ming Liang ◽  
Yue Ding ◽  
Yan Duo ◽  
Weike Yuan ◽  
Gangfeng Wang
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Yield Stress ◽  
Contact Area ◽  
Present Model ◽  
Rough Surfaces ◽  
Perfectly Plastic ◽  
Circular Model ◽  
Linear Load ◽  
Elastic Perfectly Plastic

Abstract In this paper, an incremental equivalent contact model is developed for elastic-perfectly plastic solids with rough surfaces. The contact of rough surface is modeled by the accumulation of circular contacts with varying radius, which is estimated from the geometrical contact area and the number of contact patches. For three typical rough surfaces with various mechanical properties, the present model gives accurate predictions of the load-area relation, which are verified by direct finite element simulations. An approximately linear load-area relation is observed for elastic-plastic contact up to a large contact fraction of 15%, and the influence of yield stress is addressed.

Algorithms for Dynamic Hardness Measurements by Scratch Testing in the Submicron and Nanometer Scale

2013 ◽  
Vol 853 ◽  
pp. 619-624
Author(s):  
Natalia Lvova ◽  
K. Kravchuk ◽  
I. Shirokov
Keyword(s):  
Contact Area ◽  
Scanning Probe Microscopy ◽  
Scanning Probe ◽  
Nanometer Scale ◽  
Geometrical Parameters ◽  
Scratch Testing ◽  
Dynamic Hardness ◽  
Probe Microscopy ◽  
Parameters Analysis

The automatic scratch geometrical parameters analysis algorithms based on the images obtained by scanning probe microscopy have been developed. We provide a description of the technique to determine the contact area and the scratch volume with and without account of the pile-ups. The developed algorithms are applied to measure the dynamic hardness by sclerometry on the submicron and nanometer scale.

scholarly journals A FEM analysis of the settlement of a tall building situated on loess subsoil

2020 ◽  
Vol 10 (1) ◽  
pp. 519-526
Author(s):  
Krzysztof Nepelski
Keyword(s):  
Fem Analysis ◽  
Actual Process ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Modified Cam Clay ◽  
Linear Behaviour ◽  
Subsequent Calculation ◽  
Elastic Perfectly Plastic ◽  
Subsoil Model ◽  
Storey Building

AbstractIn order to correctly model the behaviour of a building under load, it is necessary to take into account the displacement of the subsoil under the foundations. The subsoil is a material with typically non-linear behaviour. This paper presents an example of the modelling of a tall, 14-storey, building located in Lublin. The building was constructed on loess subsoil, with the use of a base slab. The subsoil lying directly beneath the foundations was described using the Modified Cam-Clay model, while the linear elastic perfectly plastic model with the Coulomb-Mohr failure criterion was used for the deeper subsoil. The parameters of the subsoil model were derived on the basis of the results of CPT soundings and laboratory oedometer tests. In numerical FEM analyses, the floors of the building were added in subsequent calculation steps, simulating the actual process of building construction. The results of the calculations involved the displacements taken in the subsequent calculation steps, which were compared with the displacements of 14 geodetic benchmarks placed in the slab.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

On the Conditions to Prevent Plastic Shakedown of Structures: Part I—Theory

1993 ◽  
Vol 60 (1) ◽  
pp. 15-19 ◽  
Author(s):  
Castrenze Polizzotto
Keyword(s):  
Mechanical Load ◽  
Plastic Material ◽  
Perfectly Plastic ◽  
Shakedown Theory ◽  
Elastic Perfectly Plastic ◽  
Plastic Shakedown ◽  
Steady Load

For a structure of elastic perfectly plastic material subjected to a given cyclic (mechanical and/or kinematical) load and to a steady (mechanical) load, the conditions are established in which plastic shakedown cannot occur whatever the steady load, and thus the structure is safe against the alternating plasticity collapse. Static and kinematic theorems, analogous to those of classical shakedown theory, are presented.

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