共查询到20条相似文献,搜索用时 0 毫秒
1.
The process of dislocation multiplication has been described hv chaos theory, trying to reveal the connection between the microstructures on the mesoscopic scale and the mechanical properties of material on the macroscopic scale. The relationship between the dislocation velocity exponent and the maximum of strain rate is given. The results obtained from logistic equation with exponent and the dislocation multiplication dynamic equation are compared. A scale law in one-dimension-map model with exponent is shown when the exponents of equations are changed. 相似文献
2.
This article reports the effect of hardness of erodent particles on velocity exponent of some weld deposited alloys. Three steels and two alloy cast irons were selected for the present investigation. The bulk hardness of the alloys was in the range of 300 to 800 HV, whereas erodnet particles were having hardness in the range of 400 to 1875 HV. Erosion tests were conducted with 125-150 µm cement clinker, 125-150 µm blast furnace sinter, 100-150 µm silica sand, and 125-150 µm alumina particles and at impingement angles of 30° and 90° and with impingement velocities in the range of 25 to 120 m sec-1. The erosion rate showed power-law dependence on impingement velocity, E = kVn, where kis a constant and nis the velocity exponent. The velocity exponents obtained in the present work were in the range of 1.91 to 2.52. The velocity exponent showed an increasing trend with increasing hardness of the alloys irrespective of the hardness of the erodent particles and the impingement angle. The velocity exponent increased with increasing hardness of erodent particles, irrespective of the impingement angle and hardness of the alloys. The velocity exponents obtained in the present work were rationalized with respect to erodent particle properties, material properties and erosion mechanisms. 相似文献
3.
An investigation has been made of the disloca-tion distribution and dislocation free zone near thecrack tip in bulk Fe-3% Si single crystal duringdeformation in SEM.It has been found that anumber of dislocations were emitted from the cracktip during deformation.After that,the dislocationsmoved rapidly away from the crack tip,which indi-cated that they were strongly repelled by the stressfield at the crack tip.Between the crack tip and theplastic zone there is a region of dislocation-free,which is referred to as dislocation-free zone (DFZ).The length of DFZs is roughly estimated 100μm which is much longer than that found in thinfoil specimen.The variation of dislocation densityas a function of the distance from the crack tip wasmeasured,which showed that the dislocations areinversely piled up in the plastic zone.The length ofDFZs increased with both the length of pre-crackand the amplitude of applied stress. 相似文献
4.
A special constant deflection device for TEM has been designed and then the dislocation configuration change ahead of a loaded crack tip after corrosion or anodic dissolution for some time but before the initiation of SCC can be observed in TEM. The results showed that anodic dissolution during SCC of a type 310 stainless steel in deionized water could promote dislocation emission,multiplication and motion before the initiation of SCC. 相似文献
5.
6.
By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that only the location of tension or compression stress fields of the dislocations are favorable for martensite nucleation in NiAl alloy and the dislocations can move to accommodate partly the transformation strain during the nucleation and growth of martensite. Combined with the molecular dynamics simulation, a two dimensional simulation for martensite morphology based on a dislocation model has been performed. Many factors related to martensitic transformation were considered, such as supercooling, interface energy, shear strain, normal strain and hydrostatic pressure. Different morphologies of martensites, similar to lath, lenticular, thin plate, couple-plate and lenticular couple-plate martensites observed in Fe-C and Fe-Ni-C alloys, were obtained. 相似文献
7.
Behaviour of layered steel fibre reinforced cementitious composite (SFRCC) panels is studied under high velocity impact of short projectiles. The panels consist of slurry infiltrated fibre concrete (SIFCON) layers in external faces and an intermediate (core) layer of latex modified concrete (LMC) and steel wire mesh embedded in cement sand slurry. In order to minimize acoustic impedance mismatch at the interfaces, judiciously selected materials are provided in the layers with appropriate lay-up sequences. For relative evaluation of high velocity impact performances of these panels', impact experiments are conducted in controlled environment. Two most commonly used types of short projectiles having calibre diameter of 5.56 mm and 7.62 mm are used in this study. Various important response parameters like depth of penetration (DOP), crater size, spalling, and cracking in the panels are considered for the performance evaluation. This paper presents the results of experimental study conducted on SFRCC panels. Considering the results obtained from experimental study, relative assessment of impact performances of SFRCC panels is carried out with respect to the materials of core layer. Influence of steel fibre volume on impact performance of the panels is also investigated and expressions are proposed based on regression analysis. In order to determine the residual impact resistance of the SFRCC panel after first hit, the same panel was impacted consecutively two to three times, generally within the damage zone of the first hit. Promising potential to resist high velocity impact is exhibited by the SFRCC panels. The structural integrity of the SFRCC panels is found intact even under multiple hits. 相似文献
8.
为提高对爆破振动速度预测的准确性,提出一种基于相关向量机(RVM)的爆破振动速度预测模型.利用该模型建立爆破振动速度与其影响因素之间的非线性映射关系,通过选取影响爆破振动速度的3个主要因素(炸药用量、距离、高程差),并对这3个主要影响因素产生的36组数据进行拟合训练,根据这36组训练样本来对剩余5组样本进行精准预测.将... 相似文献
9.
O. Abah O. A. Ogbuu C. M. I. Okoye 《Journal of Superconductivity and Novel Magnetism》2013,26(4):1195-1198
Analytical calculations of isotope effect exponent of both s-wave and π-phase-shifted s-wave two-band superconductors are presented within the framework of Bogoliubov–Valatin formalism using three-square-well model approach. The effective pairing interaction consists of contributions from the attractive acoustic electron–phonon, optical electron–phonon contributions in addition to repulsive electron–electron or antiferromagnetic fluctuation mediated pairing contributions for the diboride or pnictide superconductors, respectively. These are used to obtain analytical results that are applied in studying the isotope effect exponent in the diboride and pnictide superconductors, and the results are compared with experimental data. 相似文献
10.
11.
12.
13.
An etchant to reveal the non-basal dislocations on the (0001) faces of MoS2 single crystals has been established. Evidence concerning the ability of this etchant to reveal the sites of non-basal screw dislocations is also given. 相似文献
14.
In this study the macroscopic analysis proposed by Schapery has been applied to model the non-linear viscoelastic and viscoplastic
behaviour of polyester fibres. First, a special non-contact extensometry method has been developed in order to measure the
fibre response without affecting the behaviour of these extremely anisotropic fibres. An accelerated identification method
has then been developed. This enables a unique and independent set of parameters to be determined, which separate the reversible
and non-reversible mechanisms responsible for measured strains. The model prediction for an arbitrary loading sequence corresponds
closely to the measured strains. The model has been applied here at the yarn level but can equally well be used to predict
rope behaviour, either by including the identified parameters in a rope structure analysis or by identifying parameters at
the rope level. 相似文献
15.
16.
17.
Gas multiplication factors were measured in a proportional counter filled with high-purity ethylene in the pressure range 10-40 Torr. The multiplication factors were measured as a function of the reduced electric field S(a). The results show that, within the range of the high values of reduced electric field applied in this work (2648 < or = S(a) < or = 6455 V cm(-1) Torr(-1)), the reduced first Townsend coefficient alpha/P for ethylene may still be considered a function of S(a) alone. Good agreement was found with a model proposed by Akande. 相似文献
18.
《Journal of Computer-Aided Materials Design》1999,6(2-3):157-164
A simulation of dislocation dynamics has been used to calculate the critical stress for a threading dislocation moving in
a confined geometry. The optimum conditions for conducting simulations in systems of various sizes, down to the nanometer
range, are defined. The results are critically compared with the available theoretical and numerical estimates for the problem
of dislocation motion in capped layers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
20.