共查询到20条相似文献,搜索用时 15 毫秒
1.
The effect of interstitial hydrogen atoms on the evolution of plastic deformation in a crystal at the tip of a tensile crack is estimated taking into account gas exchange at the crack banks. It is found that, for an initial concentration of not less than 10?4, the plasticizing effect of dissolved hydrogen causing a dislocation expulsion is significant and can be responsible (at least, partially) for plasticization. As regards the evolution of the distribution of hydrogen atoms, a monotonic drain of dissolved hydrogen atoms into the hollow of the crack is observed for concentrations below 5×10?4, while at higher concentrations the impurity concentration at the banks of the crack varies periodically: complete drain is replaced by the accumulation of hydrogen corresponding to a “blocking” of the drain by the gas pressure. Numerical calculations are made for an α-Fe crystal. 相似文献
2.
3.
The paper proposes a discrete-continual method of excitable cellular automata for simulating the stress-strain state at crack tips and in notches with account of lattice curvature and plastic distortion through ion motion from lattice sites to interstices. The proposed nonlinear method allows one to determine the crack type and the character of fracture, to predict the possibility of dynamic rotations and structural turbulence, and to describe the processes of nonlinear wave structural transformations in strain localization bands involved in microporosity and tearing mode cracking. 相似文献
4.
The effect of a constant electric current on the migration of interstitial atoms dissolved in a crystal in the region of a tensile crack tip is estimated. The calculation takes into account plastic deformation that is produced in the vicinity of the crack tip in the loaded sample by dislocation motion in active slip planes of the crystal under the action of mechanically and electrically induced shear stresses, Joule heat release, the Thomson effect, and ponderomotive forces and allows for the effect of gas exchange near the crack edges on the evolution of the distribution of interstitial impurity atoms. The time dependence of the stress intensity factor is found for both the cases of the presence and absence of a constant electric current near the crack tip. Numerical calculations are performed for an α-Fe crystal. 相似文献
5.
P. A. Zhilyaev A. Yu. Kuksin V. V. Stega?lov A. V. Yanilkin 《Physics of the Solid State》2010,52(8):1619-1624
The plastic deformation and the onset of fracture of single-crystal metals under shock-wave loading have been studied using aluminum as an example by the molecular dynamics method. The mechanisms of plastic deformation under compression in a shock wave and under tension in rarefaction waves have been investigated. The influence of the defect structure formed in the compression wave on the spall strength and the fracture mechanism has been analyzed. The dependence of the spall strength on the strain rate has been obtained. 相似文献
6.
Elastic–plastic stress analysis has been carried out for the plastic zone size and crack tip opening displacement of a sub-interface crack with small scale yielding. In our study, the shape of plastic zone is assumed as a long, slim strip at both crack tips. In the plastic zone, both normal stress and shear stress exist and are considered due to the bi-material interface. The values of the plastic zone size, normal stress and shear stress are determined by satisfying the conditions where both Modes I and II stress intensity factors vanish and Von Mises yield criterion is met. In the present paper, the sub-interface crack is simulated by continuously distributed dislocations which will result in singular integral equations. Those singular integral equations can be solved by reducing them to a set of linear equations. The values of the plastic zone size and crack tip opening displacement are obtained through an iterative procedure. Finally, the effect of normalized loading, normalized crack depth (distance to the interface) and Dundurs’ parameters on the normalized plastic zone size and the normalized crack tip opening displacement is discussed. 相似文献
7.
The theory of structural transformations in the planar sybsystem (surface layers and internal interfaces) of solids under plastic deformation is developed. The theory is based on a consideration for local curvature of the crystal lattice, with new structural states arising in its interstices, responsible for plastic distortion. To satisfy the superplastic condition, such high-rate mechanisms should develop in both planar and 3D crystal subsystems. In a translation-invariant crystal, this condition is met by concentration fluctuations. The multiscale criterion of superplasticity is formulated based on the scale invariance of plastic deformation of the planar and crystal subsystems in a deformable solid. Beyond the criterion, superplasticity passes to the creep mode with restricted plasticity of the material. 相似文献
8.
The evolution of the distribution of interstitial impurity atoms in the plastic zone around the tip of a tension crack is
analyzed. The transport of point defects is determined by: 1) the hydrostatic component of the elastic stress at the crack
tip, created by the superposition of the elastic fields of the crack and dislocations; 2) the elastic field of moving dislocations
(“sweeping out” of interstitial impurity atoms); 3) the dislocation-driven transport of point defects present in the dislocation
cores. The contributions of each mechanism of transport of point defects to the crack tip are calculated over the entire time
from the start of loading of a sample containing a crack until an equilibrium distribution of plastic deformation is established
after the cessation of loading. Numerical calculations are carried out for interstitial hydrogen atoms dissolved in an α-Fe crystal.
Fiz. Tverd. Tela (St. Petersburg) 39, 1580–1585 (September 1997) 相似文献
9.
Here we consider high-rate deformation in solids in the context of a nonlocal transport theory, present a dynamic stress-strain diagram with elastic and plastic portions defined from a single standpoint, determine the conditions for pulse stress accumulation, and propose a mathematical model of momentum and energy exchange between scales and an instability criterion for transient plastic flow under shock loading. Phe instability criterion for high-rate deformation is verified by the example of shock loading of high-strength 30CrNi4Mo steel. 相似文献
10.
11.
V. I. Sugakov 《Physics of the Solid State》1997,39(3):434-438
It is shown that a double-well potential can appear under mechanical loads for atoms in rows parallel to the axis of a screw
dislocation and located near the nucleus of a dislocation and under dislocation slip conditions atoms can be accelerated up
to energies much higher than the binding energy of atoms in a crystal.
Fiz. Tverd. Tela (St. Petersburg) 39, 499–504 (March 1997) 相似文献
12.
Acoustic relaxation in undeformed and plastically deformed CsI single crystal has been studied using the composite oscillator
technique at frequencies (1–7) × 105 Hz in the temperature range 2–15 K. Plastic deformation leads to appearance of an internal friction peak localized in the
temperature interval 4–5 K. It is shown that the peak shifts towards higher temperatures when increasing the vibration frequency
and corresponds to a thermally activated relaxation process with very low values of the activation energyU ≈ 1.9×10−3 eV and the attack frequencyν
0≈6.7 × 103 s−1. Interaction of sound with dislocation kinks migrating in the second order Peierls relief is considered as a possible mechanism
of the peak.
Research was made possible in part by Grants U9T000 and U9T200 from the International Science Foundation and supported in
part by the Fundamental Research Foundation of Ukraine (Project 2.4/156 “Bion”). 相似文献
13.
Plastic deformation induces an enhancement in the concentration of paramagnetic trapped-hole defects in MgO crystals which contain hydroxyl ions, but not in crystals which are hydrogen-free. EPR, ENDOR and Infrared absorption measurements of hydrogen-containing crystals indicate that deformation stimulates the conversion of existing vacancies to their trapped-hole counterparts, the VA1, VOH and VF centers. There is no evidence that new impurity-compensated or intrinsic cation vacancies are produced in any crystal by deformation. 相似文献
14.
Variation of the velocity of ultrasound propagation in polycrystalline aluminum under plastic deformation is studied. The dependences of the velocity of ultrasound on the strain and the actual stress are found to consist of three distinct stages. The study of the complex shapes of these dependences allows one to reveal additional stages in the parabolic stress-strain curve of the plastic flow, these features being impossible to observe by conventional methods. The behavior of the ultrasonic velocity observed in the experiment is explained by the changes in the defect structure of the material under deformation. 相似文献
15.
L.W. Li 《Applied Surface Science》2009,255(18):7841-7845
The effect of humidity on subcritical crack growth of indentation crack in lead zirconate titanate (PZT) ferroelectric ceramics under various sustained electric field has been investigated. The results showed that subcritical crack growth of indentation crack could occur in humid air of 60%RH without electric field but did not in air with RH ≤ 30%. The subcritical crack growth could occur in vacuum under a sustained electric field of E/EC = 0.14. The incubation time decreased and the amount of the subcritical crack growth increased with increasing the humidity under the sustained field. The threshold electric field for subcritical crack growth decreased with increasing the humidity. 相似文献
16.
N. A. Tyapunina V. V. Blagoveshchenskii G. M. Zinenkova Yu. A. Ivashkin 《Russian Physics Journal》1982,25(6):569-578
Conclusions The process of plastic deformation under the action of ultrasound differs in a number of ways from deformation under static loading; a computer simulation has shown that these differences are attributable to the specific characteristics of the operation of a source of dislocations for a periodic law of variation of the stresses. Among the most significant features of the ultimate dislocation structure are the saturation of the density of defects (attainment of limiting states) and the formation of stable dislocation clusters, which do not produce stress fields.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 118–128, June, 1982. 相似文献
17.
Zu Wei Yan Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):531-538
A variational theory is proposed to study the surface states of electrons in a semi-infinite ternary mixed crystal, by taking
the effect of electron-surface optical (SO) phonon interaction into account. The energy and the wave function of the electronic
surface-states are calculated. The numerical results of the energies of the surface states of the polarons and the self-trapping
energies are obtained as functions of the composition x and surface potential V0 for several ternary mixed crystal materials. The results show that the electron-phonon interaction lowers the surface-state
levels with the energies from several to scores of meV. It is also found that the self-trapping energy of the surface polaron
has a minimum at some middle value of the composition x. It is indicated that the electron-phonon coupling effect can not be neglected.
Received 4 January 1999 and Received in final form 7 January 2000 相似文献
18.
Mechanisms of plastic deformation of bismuth single crystals that are operative upon the deformation of the (111) plane using
a Berkovich indenter at a loading rate of 1–10 mN/s were studied. The plastic deformation in the range of the loading rates
studied was established to occur mainly by pyramidal slip. 相似文献
19.
20.
R.W. Tustison 《Solid State Communications》1976,19(11):1075-1078
The low alternating field susceptibility at the temperature of the cusp of severely deformed Cu75Mn25 is an order of magnitude lower than that of the aged alloy. Steady field magnetization measurements indicate that the large changes in the magnetic properties associated with the different metallurgical conditions may be described in terms of changes in the short- range magnetic order. 相似文献