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1.
为定量测试喷射沉积合金GP区周围的晶格应变的分布,利用喷射成形技术制备了Al12Zn2.4Mg1.1Cu合金。随后对合金进行热挤压、758K固溶2小时和393K时效20小时处理。利用高分辨透射电子显微镜(High Resolution Transmission Electron Microscopy,HRTEM)和几何相位分析(Geometric Phase Analysis,GPA)软件对GP区的结构和应变场进行了测量和分析。结果表明,GP区附近的应变值在各方向差别较大,沿GP区惯习面法线方向的应变最大(εxx=-0.092),与惯习面平行方向上的应变最小(εyy=-0.004)。该项结果可解释GP区附近位错运动的差异:由于应变场在各方向上存在较大差别,产生的应变强化效果不同,导致阻碍位错运动的能力也有所不同。 相似文献
2.
Alexander Y. Klimenko Andreas G. Class Sean O'Gorman 《Flow, Turbulence and Combustion》2002,69(2):95-122
Most of the asymptotic considerations of the interaction of premixed flames with a general flow, i.e. curved and stretched
flames subjected to time dependent flow, are dedicated to high activation energy asymptotes. Therefore, in these considerations
the reaction zone is thin and the temperature within the reaction zone is constant to the leading order of approximation.
Here we consider an order unity activation energy for near-equidiffusion flames and show that the flame speed relations obtained
are distinct from those obtained by high activation energy asymptotes. The flame is assumed to be thin in comparison with
the flow scales but the reaction zone is no longer thin in comparison with the flame width. Although obtaining analytical
solutions is problematic even for undisturbed flames with wide reaction zones, we found that the propagation speed of disturbed
premixed flames with wide reaction zones is determined by analytical integrals involving the temperature profile of the undisturbed
flame. We also found independent effects of curvature and stretch for the flames with wider reaction zones.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
We study homoclinic behaviour in resonance zones of nonconservative,forced oscillators represented as one-parameter families of periodicperturbations of planar Hamiltonian systems. We use a Melnikov-typetechnique and obtain a simple condition under which separatrixsplittings with exponentially small upper bounds may occur. Todemonstrate our theory, we give two examples for Duffing-typeoscillators and compare the theoretical results with numericalsimulations. In these examples, homoclinic behaviour that was notreported in early work is detected. 相似文献
4.
The results of numerical integration of the Euler equations governing two-dimensional and axisymmetric flows of an ideal (inviscid and non-heat-conducting) gas with local supersonic zones are presented. The subject of the study is the formation of shocks closing local supersonic zones. The flow in the vicinity of the initial point of the closing shock is calculated on embedded, successively refined grids with an accuracy much greater than that previously achieved. The calculations performed, together with the analysis of certain controversial issues, leave no doubt that it is the intersection of C ?-characteristics proceeding from the sonic line inside the supersonic zone that is responsible for the closing shock formation. 相似文献
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Method of Negative Saturations for Modeling Two-phase Compositional Flow with Oversaturated Zones 总被引:2,自引:1,他引:1
We examine the two-phase flow through porous media of multicomponent partially miscible fluids. The composition of both the
phases is variable in space and time and is assumed to be in local thermodynamic equilibrium. One of the basic problems in
modeling such systems is related to the appearance of single-phase zones occupied by the fluid which is over- (or under-)
saturated, i.e., it is significantly remote from the equilibrium two-phase region. In an oversaturated zone, the two-phase
flow equations degenerate and can no longer be used, which provokes serious numerical problems. We propose to describe the
two-phase and oversaturated single-phase zone by a uniform system of classic two-phase equations while extending the concept
of the phase saturation so that it may be negative and higher than one. Physically this means that we consider the oversaturated
single-phase states as the pseudo two-phase states which are characterized by a negative saturation of the imaginary phase.
Such an extension of the concept of the phase saturation requires the development of some consistence conditions that ensure
the equivalence between the pseudo two-phase equations and the true single-phase flow model in the oversaturated zones. This
method allows using the existing numerical simulators of two-phase flow for modeling single-phase zones by adding a simple
plug-in with no modification of the structure of the simulators. The method is illustrated by several examples of hydrogene-water
flow in a waste radioactive storage and of CO2 injection in an oil reservoir. 相似文献
7.
Starting with a plane anisotropic homogeneous elasticity problem in a domain with an interior crack, we develop a mathematical
frame where nonlinear effects in the tip zones like crack kinking or plastic zones can be modeled in an enlarged state space
with the help of additional conditions at the crack tips. Using generalized Green’s formulae, we show that the solutions to
these problems turn out to minimize energy functionals which contain terms additional to the classical elastic energy and
work of external forces. They can be interpreted as performed work and energy stored in the crack tips. Within the theory
of matched asymptotic expansions, the general type of these energy functionals can be characterized in a form applicable to
mechanical problems. 相似文献
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The results of a numerical analysis of the M. A. Lavrentyev potential-vortex model for the stationary vortex zones developing behind bluff bodies in incompressible fluid flows at moderate Reynolds numbers are presented. Different methods of closing the model are estimated. 相似文献
10.
V. A. Kalinichenko 《Fluid Dynamics》2005,40(6):956-964
The results of experimentally investigating the initial stage of development of shear instability of the interface between two immiscible fluids relatively oscillating during the parametric excitation of standing internal waves are presented. Three stages of distortion of the sinusoidal wave profile are distinguished: the formation of short secondary waves, their breaking, and transition to large-scale vortex formations. It is shown that in the nodal zones of a standing wave quasi-stationary wave perturbations start to develop at wave steepnesses Γ ~ 0.08–0.13 and critical Reynolds numbers of the laminar boundary layer R ~ 90–300. The experimental data are compared with the classical Kelvin-Helmholtz theory. 相似文献
11.
The evolution and interaction of supersonic zones and the shock waves closing them are considered on the basis of the Lin-Reissner-Tsien equation for flow in plane channels with a local bottleneck.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 168–179.Original Russian Text Copyright © 2005 by Bibik, Duesperov, and Popov. 相似文献
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The model of prefracture zones is generalized to a crack between two anisotropic materials. An exact analytical solution is found on the assumptions that the prefracture zone is localized on the crack continuation and that only the normal displacements undergo discontinuity in the zone. From this solution, equations for determining the prefracture length and crack tip opening are derived 相似文献
15.
The semianalytic finite-element method is used to develop a method for solving problems of creep and continuous fracture of
complex spatial bodies. The method allows modeling the variation of the stress-strain state during creep, accompanying accumulation
of dispersed microdamages, and development of macroscopic effects—continuous fracture process zones. The growth of a continuous
fracture process zone is modeled. A criterion is formulated for determination of the applicability limits of continuum damage
mechanics. The method is exemplified by the problem of deformation and continuous fracture of a gas turbine blade
__________
Translated from Prikladnaya Mekhanika, Vol. 41, No. 9, pp. 70–86, September 2005. 相似文献
16.
The paper presents quasi-static FE-simulations of the crack formation in a reinforced concrete bar without stirrups subject to tension. The material was modeled with a continuum smeared crack model using an elasto-plastic constitutive law. A linear Rankine criterion with isotropic softening and associated flow rule was adopted in a tensile regime. To ensure the mesh-independency, the softening parameter was enhanced by a characteristic length of micro-structure by means of a non-local theory. Attention was laid to the effect of a different characteristic length of micro-structure and initial bond-slip stiffness on the spacing of localized zones. 相似文献
17.
任意圈层径向非均质土中桩的纵向振动特性 总被引:4,自引:0,他引:4
研究三维轴对称条件下径向非均质土中桩的纵向振动. 首先将桩周土体沿径向分为任意圈层来考虑土体的径向非均质性,每个圈层土体均质; 然后结合边界条件和相邻圈层土体之间接触面上位移和应力连续条件,对任意圈层土体动力平衡方程由外而内逐层求解,进而利用桩-土完全耦合条件求解桩动力平衡方程,得到桩顶的频域响应解析解和时域响应半解析解; 最后通过对土体主要控制参数的研究,得出了土体径向非均匀性对桩-土动力响应的影响. 相似文献
18.
V. Sh. Shagapov Z. A. Bulatova 《Journal of Applied Mechanics and Technical Physics》2002,43(6):902-909
A theory of local probing of borehole zones in porous and permeable rocks by means of acoustic waves is developed. Acoustic signals are assumed to propagate in an annular gap between the probe body and porous permeable wall of the borehole. Quantitative characteristics and special features of wave dynamics depending on the character of inhomogeneity of the porous medium are considered, in particular, in the case with radial fractures or a poorly permeable crust around the channel. The results obtained show that permeability and porosity of rocks in some cases exert a significant effect on evolution of acoustic signals in the borehole. 相似文献
19.
The effect zones of layer face for RCC (rolled control concrete) dam have gradual change characteristics. Based on the analysis thought of complex material, a model was built to analyze above principle of RCC dam by use of series-wound and shunt-wound connection. Some methods were proposed to determine the instantaneous Young's modulus, delayed Young's modulus and viscosity coefficient of effect zones of layer face. Above models and methods were used to mine the principle of gradual change of key calculation parameters which can response the characteristics of effect zones. The principle of gradual change was described. A model was established to analyze the three-dimensional viscoelastic problem of RCC dam. Above programs were developed. The examples show that the proposed models and methods to determine the key calculation parameters of effect zones can reflect the status of RCC dam accurately. 相似文献
20.
M.A. Bees 《Applied Scientific Research》1997,59(2-3):141-158
A deterministic mechanism for the production of plankton patches within a typical medium scale oceanic structure is proposed and investigated. By direct numerical simulation of a simple model of Langmuir circulation we quantify the effects of unsteady flows on planktonic communities and demonstrate their importance. Two qualitatively different zones within the flow are identified: chaotic regions that help to spread plankton and locally coherent regions, that do not mix with the chaotic regions and which persist for long periods of time. The relative importance of these regions to both phytoplankton and zooplankton is investigated, taking into account variations in plankton buoyancy. In particular, species-specific retention zone structure is discussed in relation to variations in environmental forcing. 相似文献