共查询到20条相似文献,搜索用时 15 毫秒
1.
The effect of the crystallographic orientation of a single crystal hollow cylinder on features of creation and evolution of plastic deformation in it under conditions of high-speed axisymmetric load is studied. An advantage of the proposed loading scheme is the simultaneous implementation of all loading variants within the chosen crystallographic base plane of the cylinder and reaching different degrees of deformation over the cross section of the sample. Using the molecular-dynamic modeling, the difference in deformation properties of the loaded sample has been shown depending on the chosen crystallographic orientation of the base plane. Results of the investigation can be used to understand the main mechanisms of the plastic deformation of crystalline bodies. 相似文献
2.
The paper reports on research in the deformation and fragmentation mechanisms of coarse- and fine-grained materials under high-rate loading. The study was performed by an experimental procedure based on collapse of thick-walled hollow cylinders and by molecular dynamics simulation. The key issue was to study the formation of plastic strain localization bands. It is found that the pattern of plastic deformation is governed by loading conditions and characteristic grain sizes. For a coarse-grained material, the governing mechanism is dislocation deformation resulting in localization bands. For a fine-grained material, the governing mechanism is grain boundary sliding with attendant fragmentation of the material. A dependence of the strain rate and degree on the critical grain size was disclosed. The computer simulation revealed mechanisms of grain boundary sliding on the scales studied. 相似文献
3.
V. I. Betekhtin V. Sklenicka A. G. Kadomtsev Yu. R. Kolobov M. V. Narykova 《Physics of the Solid State》2017,59(5):960-966
Mechanical stability under prolonged loading and thermostability under annealing have been studied for nano- and microcrystalline titanium obtained by different methods of intense plastic deformation. The effect of nanoporosity and the fraction of high angle boundaries formed due to intense plastic deformation has been revealed and analyzed. It has been established that, depending on the loading or the annealing temperature, thermomechanical stability of titanium can be affected, apart from the above structural characteristics, by either twin grain boundaries or titanium-carbide disperse particles. 相似文献
4.
The paper studies the effect of the amount and distribution pattern of nanoinclusions in a high-strength mesocomposite matrix on its plastic deformation under dynamic loading. The study is performed on mesocomposite specimens shaped as hollow thick-walled cylinders subjected to combined shear/compression loading with an explosive. It is found that homogeneous strain decreases with the growing volume fraction of nanoinclusions. The mechanical texture formed by the distribution of nanoinclusions in mesocomposite bars is shown to influence the deformation and cracking mechanisms. Additionally, the influence of structure is studied by computer simulation. The simulation has revealed that plastic deformation is rotational in the mesocomposite with chaotic structural distribution. 相似文献
5.
The effect of interface types (namely, sharp interface and graded interface) and its thickness on the deformation behavior of crystalline/amorphous/crystalline sandwich structures (CACSSs) under tensile loading are studied using molecular dynamics simulation. Compared with the CACSSs with sharp interface, the CACSSs with gradient interface consistently exhibit good plasticity when the interface thickness is larger than 6 nm, due to the coupling effects among crystalline layer, amorphous layer and crystalline–amorphous interface. With the increase of interface thickness, the plastic deformation mechanism of CACSSs with gradient interface changes from the local plastic deformation in amorphous layer to the homogeneous plastic deformation. 相似文献
6.
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
7.
Yu. V. Petrov S. A. Atroshenko N. A. Kazarinov A. D. Evstifeev V. Yu. Solov’ev 《Physics of the Solid State》2017,59(4):661-666
The kinetics of fracture and deformation of the standard aluminum alloy AD1 and a similar alloy subjected to severe plastic deformation by high-pressure torsion under conditions of high-speed erosion has been investigated. It has been shown that, with an increase in the loading rate, the fraction of the brittle component on the fracture surface of the standard material, as well as the thickness of the damaged layer, increases more significantly than that for the material after the severe plastic deformation by high-pressure torsion. A relationship of the surface roughness of the material after the erosion with the loading rate and the thickness of the erosion-damaged layer has been established. 相似文献
8.
Methods of dynamic nanoindentation were used to study unstable modes of plastic flow in micro-and submicrovolumes of the Al-3% Mg alloy. It was established that, depending on the rate of loading and dimensions of the deformed region, various regimes of unstable plastic deformation are realized. In the course of deformation, the irregular deformation curve (corresponding to a random process) reveals a quasi-periodic behavior with a characteristic amplitude of hardness oscillations. 相似文献
9.
Yong Yang Ying Li Guowei Zhang Zailin Yang Jin Liu Hairui Li Jianwei Zhao 《Journal of nanoparticle research》2018,20(8):205
Influences of different factors on the elastic-plastic properties of nanocrystalline copper containing a void are studied by the molecular dynamics method. The radius of the circular plate is 30a, while the radius of the void is 5a (a is 0.3615 nm for the lattice constant of bulk copper). The effects of crystal orientation, the void ellipticity, loading rate, and temperature of nanocrystalline copper are discussed. The elastic-plastic deformation of nanocrystalline under inner pressure is investigated in this research. The plastic zone is determined according to the dislocation nucleation from the edge of the void. The simulation results show that there are different deformation mechanisms under different crystal orientations, and the nanocrystalline copper can be strengthened by changing the void shape, decreasing the loading rate, and lowering the temperature. And the plastic zone initiation and growth are further explained. The change of different conditions has a great influence on plastic zone. 相似文献
10.
I. V. Khomskaya V. I. Zel’dovich A. E. Kheifets B. V. Litvinov 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(11):1221-1225
Effects of shock wave interaction and the related phenomena of the localization of plastic deformation, destruction, and mass transfer in metal ball samples subjected to explosive loading at pressures of 36 to 150 GPa are studied. A correlation between the macro- and microstructural changes and the geometrical conditions of loading according to various schemes is found. It is shown that the mass transfer effects are of hydrodynamic origin. The depth penetration of the material was 3.2 mm in narrow channels and 0.3 mm in solid material. 相似文献
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Elastic–plastic deformation of Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 single crystals during nanoindentation
Meng Fei Wong 《哲学杂志》2013,93(13):1685-1700
The elastic–plastic deformation behavior of (001)- and (011)-oriented single crystal solid solutions of Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 (PZN–PT) have been studied using a nanoindentation technique. A procedure is presented here to isolate the elastic, elastic–plastic and plastic contributions to the deformation using the unloading data, and a parameter, referred to as relaxation, is defined to characterize the elastic–plastic deformation during nanoindentations. This relaxation parameter increases with the maximum indentation load due to the higher indentation stress induced, and it also causes less recovery of the material upon indentation unloading compared to predicted pure elastic recovery. For a (001) surface, the relaxation value remains virtually unchanged within the range of the maximum indentation load of 10–50 mN, possibly due to a complete localized depoling of the non-180° domain switching. It is also found that the unpoled surface is more prone to stress-induced depolarization compared to the poled surfaces. Furthermore, by applying the continuous stiffness measurement (CSM) technique, the effects of multiple loading/unloading are studied for both (001)- and (011)-oriented PZN–PTs using the maximum indentation loads of 20 and 50 mN. With more loading/unloading cycles at higher CSM frequencies, stress-induced depolarization becomes prevalent and the contribution of the domain reorientation towards elastic recovery is significantly reduced. As a consequence, the relaxation value is increased, indicating more elastic–plastic deformation. This CSM effect is especially pronounced for poled (011) surfaces. 相似文献
14.
I. A. Gindin I. M. Neklyudov I. I. Soloshenko S. A. Khizhkovaya 《Russian Physics Journal》1973,16(2):208-211
The effect of slow loading (350 g/mm2 per h) on the deformation resistance of n- and p-type germanium single crystals is studied. In the presence of a smoothly-increasing load, germanium single crystals undergo up to 22% deformation at 400°C without rupture. Germanium crystals subjected to preliminary slow loading yield in a plastic manner on subsequent subjection to ordinary tensile tests, even in the temperature range corresponding to the brittle fracture of the original samples.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 86–90, February, 1973. 相似文献
15.
Sergey G. Psakhie K. P. Zolnikov A. I. Dmitriev D. S. Kryzhevich A. Yu. Nikonov 《Physical Mesomechanics》2012,15(3-4):147-154
The work is a molecular dynamics study of the peculiarities of local structural transformations in a copper crystallite at the atomic level in contact interaction of various types: shear loading of perfectly conjugate surfaces, local shear loading and nanoindentation. Interatomic interaction is described in the framework of the embedded atom method. It is shown that initial accommodation of the loaded crystallite proceeds through local structural transformations giving rise to higher-rank defects such as dislocations, stacking faults, interfaces, etc. In further plastic deformation, the structural defects propagate from the contact zone to the crystallite bulk. The egress of structural defects to a free surface causes deformation of the model crystallite. The deformation pattern can evolve, depending on the loading conditions, with a change in crystallographic orientation of the crystallite near the contact zone, generation of misoriented nano-sized regions, and eventually formation of a stable nanostructural state. The obtained results allow conceptually new understanding of the nature of defect generation in a crystalline structure during the nucleation and development of plastic deformation in loaded materials. 相似文献
16.
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
17.
I. V. Khomskaya V. I. Zel’dovich N. Yu. Frolova E. V. Shorokhov I. N. Zhgilev A. E. Kheifets 《Russian Journal of Physical Chemistry B, Focus on Physics》2007,1(6):630-634
Structural changes in copper samples subjected to severe plastic deformation with the use of the dynamic loading technique were studied. The deformation was caused by pressing blanks through two or three channels situated at an angle with respect to one another. The velocity of a blank before it got into the first channel was 280–450 m/s. Pressure in samples did not exceed 3–7 GPa. The microstructure of copper changed under the simultaneous action of high-velocity deformation and temperature increase. The formation of cellular dislocation structures, systems of microtwins, dynamic polygonization subgranular structures, and new recrystallized grains was observed. After two passes, the major part of a sample had a structure that consisted of thin fibers containing submicrodisperse (50–100 nm) grains. 相似文献
18.
Wun-Kai Wang Hua-Chiang Wen Chun-Hu Cheng Wu-Ching Chou Wei-Hung Yau Ching-Hua Hung Chang-Pin Chou 《Journal of Physics and Chemistry of Solids》2014
We used atomic layer deposition to form ZnO thin-film coatings on Si substrates and then evaluate the effect of pile-up using the nanoscratch technique under a ramped mode. The wear volume decreased with increasing annealing temperature from room temperature to 400 °C for a given load. Elastic-to-plastic deformation occurred during sliding scratch processing between the groove and film for loading penetration of 30 nm. The onset of non-elastic behavior and greater contact pressure were evident for loading penetration of 150 nm; thus, full plastic deformation occurred as a result of a substrate effect. We suspect that elastic–plastic failure events were related to edge bulging between the groove and film, with elastic–plastic deformation attributable to adhesion discontinuities and/or cohesion failure of the ZnO films. 相似文献
19.
Experimental and numerical studies of nonlinear ultrasonic responses on plastic deformation in weld joints 下载免费PDF全文
The experimental measurements and numerical simulations are performed to study ultrasonic nonlinear responses from the plastic deformation in weld joints. The ultrasonic nonlinear signals are measured in the plastic deformed30Cr2Ni4 Mo V specimens, and the results show that the nonlinear parameter monotonically increases with the plastic strain, and that the variation of nonlinear parameter in the weld region is maximal compared with those in the heat-affected zone and base regions. Microscopic images relating to the microstructure evolution of the weld region are studied to reveal that the change of nonlinear parameter is mainly attributed to dislocation evolutions in the process of plastic deformation loading. Meanwhile, the finite element model is developed to investigate nonlinear behaviors of ultrasonic waves propagating in a plastic deformed material based on the nonlinear stress–strain constitutive relationship in a medium. Moreover, a pinned string model is adopted to simulate dislocation evolution during plastic damages. The simulation and experimental results show that they are in good consistency with each other, and reveal a rising acoustic nonlinearity due to the variations of dislocation length and density and the resulting stress concentration. 相似文献
20.
A. V. Makarov R. A. Savrai E. S. Gorkunov A. S. Yurovskikh I. Yu. Malygina N. A. Davydova 《Physical Mesomechanics》2015,18(1):43-57
In the work, we studied the special features of deformation and fracture of quenched steel 50 (0.51%) under static and cyclic tension after combined strain-heat nanostructuring treatment, which includes fictional treatment with subsequent tempering at 350°C. It is shown that the combined nanostructuring treatment of quenched steel 50 changes the character of plastic flow, making it more uniform, in the loaded material. Under static tension, this shows up as disappearance of the yield plateau early in the process, and under cyclic loading, as suppression of the deformation relief formed by shear and rotational deformation modes. Despite incipient cracks, the hardened surface layer thus escapes complete fracture throughout the fatigue loading and preserves its resistance to mechanical contact action. 相似文献