130 research outputs found
Equation of motion for dislocations with inertial effects
An approximate equation of motion is proposed for screw and edge
dislocations, which accounts for retardation and for relativistic effects in
the subsonic range. Good quantitative agreement is found, in accelerated or in
decelerated regimes, with numerical results of a more fundamental nature.Comment: 6 pages, 4 figures, LaTe
Magnetostimulated Chandges of Microhardness in Potassium Acid Phthalate Crystals
A decrease in microhardness along the (010) cleavage in potassium acid
phthalate single crystals by 15--18% after the application of a permanent
magnetic field was revealed for the first time. It is shown that the effect
revealed is of the volume character. The role of interlayer water in the
processes stimulated by a magnetic field is studied., Interlayer water plays
does not cause the observed changes it only plays the part of an indicator of
these changes in potassium acid phthalate crystals in a magnetic field. It is
established that microhardness in the (100) plane of the crystal in an applied
a magnetic field first increases by 12--15% and then remains constant in time
within the accuracy of the experiment. The possibility of varying the crystal
structure of potassium acid phthalate crystals by applying magnetic fields
inducing rearrangement in the system of hydrogen bonds or in the defect
structure is discussed.Comment: 6 pages, 7 figure
Lattice Resistance to Dislocation Motion at the Nanoscale
In this letter we propose a model that demonstrates the effect of free
surface on the lattice resistance experienced by a moving dislocation in
nanodimensional systems. This effect manifests in an enhanced velocity of
dislocation due to the proximity of the dislocation line to the surface. To
verify this finding, molecular dynamics simulations for an edge dislocation in
bcc molybdenum are performed and the results are found to be in agreement with
the numerical implementations of this model. The reduction in this effect at
higher stresses and temperatures, as revealed by the simulations, confirms the
role of lattice resistance behind the observed change in the dislocation
velocity.Comment: 4 Figure
Magnetic structural effect in nonequilibrium defective solids
Scientific study of the effect of structural memory of nonequilibrium
defective solids about the processing in magnetic field (the magnetic
structural effect (MSE) was continued in this paper. The study was aimed to
reveal the universal nature of the MSE, which was investigated in several new
nonequilibrium defective solids. The results of investigation of the processing
in the vortical magnetic field (PVMF) and its effect on the structure of the
natural magnetite Fe3O4 and the SnO2 films were presented. The methods of
Mössbauer and X-ray spectroscopy were used. The PVMF reduction of a
defectiveness of Fe3O4 structure in the magnetite was detected. The MSE was
also observed in the Mössbauer spectra of diamagnetic tin oxide SnO2 films
after the PVMF. One of the possible explanations of the MSE was given in the
paper.Comment: 6 pages, 6 figures, 3 table
Atomistic simulations of dislocation mobility in Al, Ni and Al/Mg alloys
Dislocation velocities and mobilities are studied by Molecular Dynamics
simulations for edge and screw dislocations in pure aluminum and nickel, and
edge dislocations in Al-2.5%Mg and Al-5.0%Mg random substitutional alloys using
EAM potentials. In the pure materials, the velocities of all dislocations are
close to linear with the ratio of (applied stress)/(temperature) at low
velocities, consistent with phonon drag models and quantitative agreement with
experiment is obtained for the mobility in Al. At higher velocities, different
behavior is observed. The edge dislocation velocity remains dependent solely on
(applied stress)/(temperature) up to approximately 1.0 MPa/K, and approaches a
plateau velocity that is lower than the smallest "forbidden" speed predicted by
continuum models. In contrast, above a velocity around half of the smallest
continuum wave speed, the screw dislocation damping has a contribution
dependent solely on stress with a functional form close to that predicted by a
radiation damping model of Eshelby. At the highest applied stresses, there are
several regimes of nearly constant (transonic or supersonic) velocity separated
by velocity gaps in the vicinity of forbidden velocities; various modes of
dislocation disintegration and destabilization were also encountered in this
regime. In the alloy systems, there is a temperature- and
concentration-dependent pinning regime where the velocity drops sharply below
the pure metal velocity. Above the pinning regime but at moderate stresses, the
velocity is again linear in (applied stress)/(temperature) but with a lower
mobility than in the pure metal.Comment: PDF, 30 pages including figures, submitted to Modelling Simul. Mater.
Sci. En
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