MOLECULAR DYNAMIC STUDY OF A SINGLE DISLOCATION IN A TWO-DIMENSIONAL LENNARD–JONES SYSTEM

2003 ◽  
Vol 14 (04) ◽  
pp. 407-421 ◽  
Author(s):  
MIGUEL ROBLES ◽  
VILLE MUSTONEN ◽  
KIMMO KASKI
Keyword(s):  
Constant Strain Rate ◽  
Equation Of Motion ◽  
Dislocation Motion ◽  
Strain Rates ◽  
Interactive Simulation ◽  
Two Dimensional ◽  
Single Dislocation ◽  
Lennard Jones ◽  
Quasi Static Process ◽  
Dynamics Method

In this work the motion of a single dislocation in a two-dimensional triangular lattice is studied by using classical Molecular Dynamics method with the Lennard–Jones inter-atomic potential. The dislocation motion is investigated with an interactive simulation program developed to track automatically the movement of lattice defects. Constant strain and constant strain-rate deformations were applied to the system. From constant strain simulations a curve of shear stress versus dislocation velocity is obtained, showing a nonlinear power law relation. An equation of motion for the dislocation is proposed and found to be applicable when the movement of dislocation follows a quasi-static process. Numerical simulations at different strain rates show an elastic-to-plastic transition that modifies the dynamics of the dislocation motion.

DYNAMICS OF A DISLOCATION SET IN MOTION BY AN EXTERNAL STRESS

2002 ◽  
Vol 13 (01) ◽  
pp. 97-105 ◽  
Author(s):  
M. ROBLES ◽  
L. PERONDI ◽  
K. KASKI
Keyword(s):  
Shear Stress ◽  
Dislocation Motion ◽  
External Stress ◽  
Atomic Scale ◽  
Dislocation Velocity ◽  
Two Dimensional ◽  
Tracking Method ◽  
Stress Pulse ◽  
Lennard Jones ◽  
Dynamics Simulations

The relation between dislocation velocity and resolved shear stress is studied computationally at the atomic scale using Molecular Dynamics simulations in a two-dimensional Lennard–Jones system. Mimicking a well known experimental technique, we apply a calibrated stress pulse to a system with a single dislocation and follow with a run-time graphics tool and displacement-field based tracking method, the dislocation motion caused by momentum transfer from an externally generated stress pulse. The empirically suggested power law relation between dislocation velocity and resolved shear stress seems to hold also in the atomic scale.

Comparison of Recovery and Recrystallization in Stainless Steel Following Plane-Wave Shock Loading and Explosive Forming

1970 ◽  
Vol 28 ◽  
pp. 428-429 ◽  
Author(s):  
J. A. Korbonski ◽  
L. E. Murr
Keyword(s):  
Stainless Steel ◽  
Shock Loading ◽  
Pressure Pulse ◽  
Shock Pressure ◽  
304 Stainless Steel ◽  
Strain Rates ◽  
Two Dimensional ◽  
Aisi 304 Stainless Steel ◽  
Aisi 304 ◽  
Explosive Forming

Comparison of recovery rates in materials deformed by a unidimensional and two dimensional strains at strain rates in excess of 104 sec.−1 was performed on AISI 304 Stainless Steel. A number of unidirectionally strained foil samples were deformed by shock waves at graduated pressure levels as described by Murr and Grace. The two dimensionally strained foil samples were obtained from radially expanded cylinders by a constant shock pressure pulse and graduated strain as described by Foitz, et al.

The Effects of Physical Ageing and of Prior Immersion on the Esc Behaviour of Polycarbonate in Ethanol

1993 ◽  
Vol 305 ◽  
Author(s):  
J. C. Arnold ◽  
A. R. Eccott
Keyword(s):  
Strain Rate ◽  
Immersion Time ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Strain Rates ◽  
Physical Ageing ◽  
Diffusion Effects ◽  
Craze Initiation ◽  
Comparison Of Tests

AbstractThe effects of physical ageing and prior immersion time on the ESC behaviour of polycarbonate in ethanol were studied. Constant strain rate tensile tests were performed at a range of strain rates for samples with ageing times varying from 100 hours to 3000 hours and for prior immersion times of between 1 hour and 500 hours. Comparison of tests performed in ethanol and in air gave a good indication of the point of craze initiation. The results showed that there was a reduction in strain to crazing as the strain rate decreased, apart from with the lowest strain rate used. A longer prior immersion time also promoted craze formation. Both of these results are attributable to diffusion effects. Physical ageing had little effect on the ESC behaviour, due to the large amounts of deformation encountered in this system.

Motion of a charged particle in superposed Heliotron and biconical cusp fields

1969 ◽  
Vol 3 (2) ◽  
pp. 255-267 ◽  
Author(s):  
M. P. Srivastava ◽  
P. K. Bhat
Keyword(s):  
Magnetic Field ◽  
Charged Particle ◽  
Magnetic Moment ◽  
Particle Trajectory ◽  
Three Dimensional ◽  
Equation Of Motion ◽  
Neutral Point ◽  
Two Dimensional ◽  
Axially Symmetric ◽  
Hybrid Type

We have studied the behaviour of a charged particle in an axially symmetric magnetic field having a neutral point, so as to find a possibility of confining a charged particle in a thermonuclear device. In order to study the motion we have reduced a three-dimensional motion to a two-dimensional one by introducing a fictitious potential. Following Schmidt we have classified the motion, as an ‘off-axis motion’ and ‘encircling motion’ depending on the behaviour of this potential. We see that the particle performs a hybrid type of motion in the negative z-axis, i.e. at some instant it is in ‘off-axis motion’ while at another instant it is in ‘encircling motion’. We have also solved the equation of motion numerically and the graphs of the particle trajectory verify our analysis. We find that in most of the cases the particle is contained. The magnetic moment is found to be moderately adiabatic.

Elasto-viscoplastic constitutive equations for the description of glassy polymers behavior at constant strain rate

2006 ◽  
Vol 129 (1) ◽  
pp. 29-35 ◽  
Author(s):  
Fahmi Zaïri ◽  
Moussa Naït-Abdelaziz ◽  
Krzysztof Woznica ◽  
Jean-Michel Gloaguen
Keyword(s):  
Constitutive Equations ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Glassy Polymers ◽  
Uniaxial Tensile ◽  
Model Parameters ◽  
Strain Rates ◽  
State Variable ◽  
Rubber Toughened ◽  
Compressive Tests

In this study, a modelization of the viscoplastic behavior of amorphous polymers is proposed, from an approach originally developed for metal behavior at high temperature, in which state variable constitutive equations have been modified. A procedure for the identification of model parameters is developed through the use of experimental data from both uniaxial compressive tests extracted from the literature and uniaxial tensile tests performed in this study across a variety of strain rates. The numerical algorithm shows that the predictions of this model well describe qualitatively and quantitatively the intrinsic softening immediately after yielding and the subsequent progressive orientational hardening corresponding to the response of two polymers, amorphous polyethylene terephthalate and rubber toughened polymethyl methacrylate.

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