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1.
The atomic structure and dynamic behavior of interstitial clusters, i.e., a bundle of <110> crowdions, have been investigated
in a model Ni lattice. An extended dislocation loop was obtained after full relaxation of a loop of hexagonal shape, consisting
of four dislocation segments lying on {111} slip planes and two dislocation segments on {100} slip planes. The dislocation
segments on {111} slip planes are extended, but the segments on {100} slip planes are not extended. By observing the motion
of a dislocation loop under axially symmetrical shear stress, the Peierls stress for the dislocation loop was obtained. Also,
a diamond-shaped dislocation loop was constructed in the model lattice, consisting of four dislocation segments on {111} slip
planes and no segments on {100} slip planes. The Peierls stress for this diamond-shaped dislocation loop was found to be less
than that for the hexagonal-shaped dislocation loop.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
In this paper, we use a simplified model to simulate the amorphization phenomenon in metals under irradiation. The model has few parameters but can reflect the essential characteristics of the processes. Our simulation results show that the relaxation of collision cascades forms small crystal grains and the amorphization phenomenon is a result of total overlap of different grains, which depends on the irradiation temperature. 相似文献
3.
The densification process during pressure sintering has been analyzed using finite element analysis. This analysis uses an
iterative solution algorithm. With this the densification process in complex geometries with complex boundary conditions can
be analyzed and this technique is particularly suited for tackling material nonlinearity. Evolution of dense structures with
gradual closure of pores is described for two typical geometries. 相似文献
4.
5.
An atomistic computer model based on a rigid boundary method has been developed to estimate the interaction energy between
a single edge dislocation and an impurity carbon interstitial in nickel. The simulation was carried out using the static relaxation
technique on a total of 600 atoms, using an appropriate host-host pair potential. The impurity-host potential has been chosen
to be a cubic function in this calculation. In the absence of the dislocation the dipole tensor for the octahedral site is
seen to be spherical. Two impurity positions, one above and one below the slip plane were investigated. The carbon-dislocation
interaction energies obtained were 1·4 eV and 0·7 eV respectively for the two impurity positions. The dipole tensor for the
impurity in the presence of the dislocation was found to be non-diagonal. 相似文献
6.
The paper presents a brief overview of different types of modelling and simulation along with the distinguishing features
between the two. Spatial as well as temporal size scales with a special reference to multiscale modelling are explained with
illustrations. The paper includes a discussion on numerical experiments and their validation based on the authors’ work on
FEM simulation of crack-tip blunting during ductile fracture. Attention is drawn to the use of a 3P technique involving integrated
simulation of deformation (property) at microstructural level, the process at macroscopic level and the performance at the
product level. 相似文献
7.
8.
In this paper, we describe the computer simulation technique and its application to the study of radiation damage. Details
of two important methods: the static and the dynamic methods have been discussed. Applications to the study of point defect
formation and stability, their clusters, diffusion, dislocations and dislocation-point defect interaction are discussed drawing
from our own work wherever possible. A short mention is made of the importance of the interatomic potential. Examples for
the case of magnesium and other hcp metals, bcc iron and fcc Ni are cited and numbers for various quantities like formation
energy, dipole tensor, interaction energy etc are quoted. 相似文献
9.
10.
基于量子力学隧穿原理,对由Au纳米粒子自组装体系构建的典型串联双隧道结模型的I-V特性进行了计算机模拟,模拟结果与实验曲线吻合。该方法对于构建纳米电子器件模型及工艺优化将具有指导意义。 相似文献
11.
The molecular ordering of 4-(6-hydroxyhexyloxy)-4′-cyanobiphenyl (H6CBP), a bipolar nematogen, has been carried out at nematic-isotropic transition temperature with respect to translatory and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment at each atomic centre. The modified Rayleigh–Schrodinger perturbation theory with multicentred-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a 6-exp potential function has been assumed for short-range interactions. The interaction energy values obtained through these computations were used to calculate the probability of each configuration at nematic-isotropic transition temperature using the Maxwell–Boltzmann formula. On the basis of stacking, in-plane, and terminal interactions energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are correlated with molecular parameters introduced in this article, and an attempt has been made to explain the nematic behaviour of the compound in terms of their relative order. 相似文献
12.
Masao Doyama 《Bulletin of Materials Science》1995,18(4):311-323
Body-centred cubic iron whiskers having [100] and [110] axes were pulled in a molecular dynamics simulation using a supercomputer.
The upper yield stress close to the theoretical strength was found. Above the upper yield stress, phase transformation was
observed; at the same time the stress was greatly reduced. A new possible mechanism of twinning is proposed. The whiskers
were pulled until they had broken into two pieces. Copper small crystals with and without a notch were sheared. It was observed
that the edge dislocations were created at the surface and moved through and escaped from the crystals. Copper small single
crystals with a notch were pulled. A half-dislocation was created near the tip of the notch. Sharp yield stress was observed.
In medium deformation dislocations on different slip planes were created. Due to the cutting of dislocations the tensile stress
increased. 相似文献
13.
Molecular dynamics (MD) has been used extensively to simulate displacement cascades in metals; and this paper contains a summary
of the progress made to date. It includes results dealing with the effect of primary knock-on atom energy and irradiation
temperature on defect formation in a variety of metals. It is shown that in addition to data on the number of defects produced,
quantitative information is available on the distribution of defects created in clusters. Thus, the nature of the primary
damage state is now clear. The successful development of multiscale models to describe the evolution of radiation damage microstructure
and its impact on material performance requires detailed atomic-level information about the stability, motion and interaction
of defects. This is starting to be obtained by MD and some recent results are discussed. The place of atomic-scale modelling
in the multiscale problem of radiation damage is shown.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
针对DHP-06型氩色谱分析仪在分析使用过程中存在高纯氩载气使用量大和分析工操作时间长等矛盾,介绍了采用氩储槽内的氩净化后做载气的改造方案. 相似文献
15.
Vijay Kumar 《Bulletin of Materials Science》1997,20(6):745-754
We present results of ourab initio molecular dynamics simulations on the atomic and electronic structure of clusters of divalent metals, aluminum and antimony,
which exhibit a range of bonding characteristics e.g. non-metal-metal transition, metallic and covalent respectively. Results
of these studies have been used to develop icosahedral AI12X (X = C, Si and Ge) superatoms with 40 valence electrons which correspond to a filled electronic shell. It is found that
the doping leads to a large gain in the binding energy as compared to Al13, suggesting this to be a novel way of developing species for cluster assembled materials. Further studies of adsorption of
Li, Si and Cl atoms on Al7 and Al13 clusters show marked variation in the adsorption behaviour of clusters as a function of size and the adsorbate. Silicon reconstructs
both the clusters and induces covalency in Al-Al bonds. We discuss the adsorption behaviour in terms of the superatom-atom
interactions. 相似文献
16.
从工艺角度看,Ar馏份中分析Ar和分析O2是一样的,但从分析仪器的角度看,分析Ar比分析O2更合理。这主要考虑到了大气压力变化对气体分析仪器讯号输出有影响。 相似文献
17.
18.
S L Chaplot 《Bulletin of Materials Science》1999,22(3):279-285
Molecular dynamics simulations, in combination with lattice dynamics studies, based on semiempirical interatomic potentials,
have been very useful in the study of properties of complex novel materials at high temperature and pressure. Various properties
such as the equation of state, elastic and thermodynamic properties, phase transitions and melting have been studied. These
studies help in understanding the synthesis of important new and novel materials, especially the amorphous materials, compounds
with unusually coordinated atoms, (e.g. with five-coordinated silicon atoms), materials with controlled thermal expansion,
etc. A few examples will be discussed from our recent studies. 相似文献
19.
AbstractThe electronic properties of silver clusters formed on the surface of reduction- sensitized octahedral and cubic AgBr emulsions were studied. Prior to sensitization with dimethylamineborane, SnCl2 or high pH, these emulsions had the same efficiency. The results suggest that the octahedral emulsion has more potential to achieve a higher maximum speed increase. This difference may be due to fewer available sites for silver cluster formation on cubic surfaces. Gelatin concentration studies showed that the gelatin and/or impurities do play a role in silver cluster formation by high pH treatment. The precise role of OH? is uncertain. 相似文献
20.
Computer simulation has been used widely in many industries for many applications. A simulation model mimics a real world system, enabling an investigation of its operation. More recently simulation models have incorporated a visual display and interactive features to aid understanding and enhance the investigation. Computer simulation has many potential uses in quality and reliability engineering, for instance, modelling equipment failures, quality control strategies, maintenance requirements and operational logistics. A case study shows how simulation has been used to study the throughput, flexibility and robustness of a manufacturing plant design. Alternative simulation software packages are briefly discussed. 相似文献