scholarly journals Incompatibility-governed elasto-plasticity for continua with dislocations

2017 ◽  
Vol 473 (2199) ◽  
pp. 20160734 ◽  
Author(s):  
Samuel Amstutz ◽  
Nicolas Van Goethem
Keyword(s):  
Dislocation Motion ◽  
Topological Derivative ◽  
Equilibrium Equations ◽  
Perfect Plasticity ◽  
Thermodynamic Variable ◽  
Plastic Behaviour ◽  
Elasto Plasticity ◽  
Novel Model ◽  
The Continuum

In this paper, a novel model for elasto-plastic continua is presented and developed from the ground up. It is based on the interdependence between plasticity, dislocation motion and strain incompatibility. A generalized form of the equilibrium equations is provided, with as additional variables, the strain incompatibility and an internal thermodynamic variable called incompatibility modulus, which drives the plastic behaviour of the continuum. The traditional equations of elasticity are recovered as this modulus tends to infinity, while perfect plasticity corresponds to the vanishing limit. The overall nonlinear scheme is determined by the solution of these equations together with the computation of the topological derivative of the dissipation, in order to comply with the second principle of thermodynamics.

An Efficient Static Analysis of Continuum Robots

2014 ◽  
Vol 6 (3) ◽  
Author(s):  
Shahir Hasanzadeh ◽  
Farrokh Janabi-Sharifi
Keyword(s):  
Real Time ◽  
Recursive Algorithm ◽  
A Priori ◽  
Real Time Control ◽  
Equilibrium Equations ◽  
Backbone Curve ◽  
Time Control ◽  
Continuum Robot ◽  
Main Component ◽  
The Continuum

An efficient yet accurate model of the continuum robot is the main component for its real-time control, simulation as well as localization. Previous models of the continuum robot, based on rod theory, suffer from high computational burden. The models also require a priori knowledge of the robot environment. This paper presents an efficient static model for the planar continuum robot that experiences external forces at the tip as a result of contact with its surroundings (measured by the built-in force sensors), thus no a priori information about the environment is required. The typical example of such robots is steerable catheters used in medical operations. The proposed approach involves discretizing the robot backbone curve to elastic arc elements. After deriving the equilibrium equations for the infinitesimal elements, a recursive algorithm with the time complexity of O(n) is proposed for realizing the shape of the robot as a result of the external force. Accuracy of the proposed method is evaluated both theoretically and experimentally for a case study, i.e., an intracardiac ablation catheter. Results validate the accuracy and time-efficiency of the proposed approach for real-time applications.

scholarly journals Prediction of fatigue crack initiation life of aluminium alloy joints using cyclic elasto-plasticity FEM analysis

2018 ◽  
Vol 165 ◽  
pp. 14012
Author(s):  
Tsutsumi Seiichiro ◽  
Sano Moe ◽  
Fincato Riccardo
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Fem Analysis ◽  
Finite Element Analyses ◽  
Butt Weld ◽  
Plastic Behaviour ◽  
Elasto Plasticity ◽  
Crack Initiation Criterion

Finite element analyses (FEA) are particularly useful for investigating fatigue problems since it is possible to carry out elasto-plastic simulations for any configuration and to predict the material behaviour for a large number of loading cycles. This study aims to investigate the fatigue life for Al-Mg alloy A5083-O joints by means of numerical simulations. The Proposed method needs to give a precise description of the elasto-plastic behaviour of the alloy together with an appropriate definition of the criteria for the fatigue crack initiation. In this paper, the elasto-plastic behaviour of the A5083-O alloy was investigated by FE analyses. On the other hand, the fatigue crack initiation criterion is provided based on strain ranges observations. In detail, the finite element analyses focused the attention on the study of the service life of a butt-weld join.

Layer Moleculecular Dynamic Diffusion Model of Nano-Meter Lubricant Film on Hard Disk Surfaces at High Rotating Speed

2008 ◽  
Author(s):  
Bo Zhang ◽  
Hiroshi Chiba ◽  
Akira Nakajima
Keyword(s):  
Film Thickness ◽  
Theoretical Prediction ◽  
Molecular Dynamic ◽  
Rheological Behavior ◽  
Rotating Speed ◽  
Wide Range ◽  
Novel Model ◽  
Dynamic Diffusion ◽  
Good Agreement ◽  
The Continuum

Spin-off experiments for PFPE Z25 were conducted by using a 3.5 inch disk at a constant speed of 10,000 rpm. The initial film thickness was set to about 2.4 nm for all the experiments while temperature was changed in a wide range. It is found that the rheological behavior of the film is quite different from that expected from the continuum. A novel model based on Fick’s law of diffusion was proposed, which is called the layer molecular dynamic diffusion (LMDD) model. The theoretical prediction was compared with the experimental results and a good agreement was obtained, verifying the effectiveness of the model.

Bifurcation Analyses of Steel and Concrete with Rate-Dependent Properties Part Two: Bifurcation Analyses and Demonstration

2002 ◽  
Vol 4 (4) ◽  
pp. 225-232
Author(s):  
Luming Shen ◽  
Yuxing Liu ◽  
Zhen Chen
Keyword(s):  
Strain Rate ◽  
Bifurcation Analysis ◽  
Critical State ◽  
Damage Model ◽  
Tangent Stiffness ◽  
Rate Dependent ◽  
Elasto Plasticity ◽  
Failure Angle ◽  
Mohr’S Circle ◽  
The Continuum

Based on the continuum tangent stiffness tensors derived in part one for steel and concrete, bifurcation analyses of rate-dependent elasto-plasticity and elasto-damage are performed in (-(and (-(spaces of Mohr, respectively. Localization ellipse osculating Mohr's circle enables us to determine the critical state and failure angle. It is shown that strain rate has no effect on the failure angle, and that the parameters in rate-dependent damage model are restricted by the results of bifurcation analysis.

Modal projections for synchronous rotor whirl

2008 ◽  
Vol 464 (2095) ◽  
pp. 1739-1760 ◽  
Author(s):  
Pradeep Mahadevan ◽  
C.S Jog ◽  
Anindya Chatterjee
Keyword(s):  
Finite Element ◽  
Dynamic Equilibrium ◽  
Mode Shapes ◽  
Simple Problem ◽  
Equilibrium Equations ◽  
Continuum Formulation ◽  
Finite Element Package ◽  
Whirl Speed ◽  
Gyroscopic Effects ◽  
The Continuum

We consider the synchronous whirl of arbitrary axisymmetric rotors supported on rigid bearings. Prior computational treatments of this problem were based on adding element-level gyroscopic terms to the governing equations. Here, we begin with a direct continuum formulation wherein gyroscopic terms need not be added on separately and explicitly: all gyroscopic effects are captured implicitly within the continuum elastodynamics. We present two new methods for obtaining the whirl speed, where we project the dynamic equilibrium equations of the rotor on to a few of its non-spinning vibration mode shapes. The first modal projection method is direct and more accurate, but requires numerical evaluation of more demanding integrals. The second method is iterative and involves a small approximation, but is simpler. Both the methods are based on one new insight: the gyroscopic terms used in other treatments are essentially the result of a prestress in the rotor caused by the non-zero spin rate, and may be incorporated as such in the continuum formulation. The accuracy of the results obtained, for several examples, is verified against detailed calculations with a commercial finite-element package, against our own nonlinear finite-element code or against analytical estimates. For further verification and illustration, a closed-form analytical solution for a simple problem, obtained using our method, matches the results obtained with explicit gyroscopic terms.

C. The Continuous Spectrum of Pulsating Variable Stars

1967 ◽  
Vol 28 ◽  
pp. 177-206
Author(s):  
J. B. Oke ◽  
C. A. Whitney
Keyword(s):  
Continuous Spectrum ◽  
Variable Stars ◽  
Velocity Fields ◽  
The Other ◽  
Line Spectrum ◽  
Direct Information ◽  
Thermodynamic Structure ◽  
Diagnostic Interpretation ◽  
Pulsating Variable Stars ◽  
The Continuum

Pecker:The topic to be considered today is the continuous spectrum of certain stars, whose variability we attribute to a pulsation of some part of their structure. Obviously, this continuous spectrum provides a test of the pulsation theory to the extent that the continuum is completely and accurately observed and that we can analyse it to infer the structure of the star producing it. The continuum is one of the two possible spectral observations; the other is the line spectrum. It is obvious that from studies of the continuum alone, we obtain no direct information on the velocity fields in the star. We obtain information only on the thermodynamic structure of the photospheric layers of these stars–the photospheric layers being defined as those from which the observed continuum directly arises. So the problems arising in a study of the continuum are of two general kinds: completeness of observation, and adequacy of diagnostic interpretation. I will make a few comments on these, then turn the meeting over to Oke and Whitney.

Photo-electric Hβ and uvby photometry

1966 ◽  
Vol 24 ◽  
pp. 170-180
Author(s):  
D. L. Crawford
Keyword(s):  
Narrow Band ◽  
Line Strength ◽  
Interference Filter ◽  
B Stars ◽  
Relative Line ◽  
The Mean ◽  
F Stars ◽  
Two Parameters ◽  
Filter Photometry ◽  
The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

Observations of the continuum near the galactic centre

1967 ◽  
Vol 31 ◽  
pp. 405
Author(s):  
F. J. Kerr
Keyword(s):  
Galactic Centre ◽  
The Past ◽  
Centre Region ◽  
The Continuum

A continuum survey of the galactic-centre region has been carried out at Parkes at 20 cm wavelength over the areal11= 355° to 5°,b11= -3° to +3° (Kerr and Sinclair 1966, 1967). This is a larger region than has been covered in such surveys in the past. The observations were done as declination scans.

Effect of Improved ThO2 Particle Dispersion in Nickel on High-Temperature Strength

1970 ◽  
Vol 28 ◽  
pp. 444-445
Author(s):  
E. R. Kimmel ◽  
H. L. Anthony ◽  
W. Scheithauer
Keyword(s):  
High Temperature ◽  
Metal Matrix ◽  
Oxide Particle ◽  
Oxide Phase ◽  
Dislocation Motion ◽  
Particle Dispersion ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Oxide Particles ◽  
The Stability

The strengthening effect at high temperature produced by a dispersed oxide phase in a metal matrix is seemingly dependent on at least two major contributors: oxide particle size and spatial distribution, and stability of the worked microstructure. These two are strongly interrelated. The stability of the microstructure is produced by polygonization of the worked structure forming low angle cell boundaries which become anchored by the dispersed oxide particles. The effect of the particles on strength is therefore twofold, in that they stabilize the worked microstructure and also hinder dislocation motion during loading.

Removing Substrate Background in TEM Microanalysis

1974 ◽  
Vol 32 ◽  
pp. 568-569
Author(s):  
John C. Russ ◽  
Nicholas C. Barbi
Keyword(s):  
Electrical Conductivity ◽  
Rapid Growth ◽  
Organic Film ◽  
Absolute Concentration ◽  
Background Signal ◽  
X Ray ◽  
Elemental Concentrations ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
The Continuum

The rapid growth of interest in attaching energy-dispersive x-ray analysis systems to transmission electron microscopes has centered largely on microanalysis of biological specimens. These are frequently either embedded in plastic or supported by an organic film, which is of great importance as regards stability under the beam since it provides thermal and electrical conductivity from the specimen to the grid.Unfortunately, the supporting medium also produces continuum x-radiation or Bremsstrahlung, which is added to the x-ray spectrum from the sample. It is not difficult to separate the characteristic peaks from the elements in the specimen from the total continuum background, but sometimes it is also necessary to separate the continuum due to the sample from that due to the support. For instance, it is possible to compute relative elemental concentrations in the sample, without standards, based on the relative net characteristic elemental intensities without regard to background; but to calculate absolute concentration, it is necessary to use the background signal itself as a measure of the total excited specimen mass.

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