Quasi-steady-state modeling of dendritic growth

A new method of the moving-boundary problem analysis is developed. After proposed coordinate transformation, the quasi-steady-state differential equation was reduced to equivalent Laplace equation. Transformed boundary conditions of a rescaled field distribution reflect the presence of rate-dependent sources on interface. Taking into account the local rate-dependence of the Neumann's boundary conditions, non-equilibrium pattern formation was considered. The problem of dendrite fractal growth was reduced to one of interaction of conformal to tips charged particles. Conditions of the quasi-steady growth and the recurrence formula for k-order dendrite spacing were derived. Theoretically obtained scaling laws for interface shape, dendrite spacing, critical sidebranch distance are confirmed by available experimental data.     

Improved Riemann solvers for complex transport in two-dimensional unsteady shallow flow

The numerical solution of advection–reaction–diffusion transport problems in two-dimensional shallow water flow is split in three subproblems in order to analyze them separately.     

A model of grain refinement and strengthening of Al alloys due to cold severe plastic deformation

This paper presents a model which quantitatively predicts grain refinement and strength/hardness of Al alloys after very high levels of cold deformation through processes including cold rolling, equal channel angular pressing (ECAP), multiple forging (MF), accumulative roll bonding (ARB) and embossing. The model deals with materials in which plastic deformation is exclusively due to dislocation movement within grains, which is in good approximation the case for many metallic alloys at low temperature, for instance aluminium alloys. In the early stages of deformation, the generated dislocations are stored in grains and contribute to overall strength. With increase in strain, excess dislocations form and/or move to new cell walls/grain boundaries and grains are refined. We examine this model using both our own data as well as the data in the literature. It is shown that grain size and strength/hardness are predicted to a good accuracy.     

Internally oxidized silver contact materials – a case for the elastoplasticity of an inhomogeneous body

The mechanical properties of oxide dispersion strengthened silver after various extrusions, which is a material optimized for electrical contacts and typical of a mechanically inhomogeneous polycrystalline state, are analysed and correlated with the arising microstructure. It is shown that the positive (in view of engineering applications) changes in yield stress and ductility can be attributed essentially to the oxide particle distribution that becomes induced increasingly homogeneous within the extruded rods by the extrusions. These changes can well be understood by a simulation of a composite on the basis of Voigt‐type averaging of elastic properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

ESPI技术对外贴纤维混凝土加固承载的实验研究

采用电子散斑干涉技术,对外贴碳纤维加固混凝土梁的外贴材料位移的分布特征,进行了全场实时测量,通过实验获得的散斑干涉条纹图可以得到外贴材料与混凝土梁的粘结传力长度随粘结长度及初始载荷之间的关系;了解用于加固的碳纤维材料的应变分布特点和产生梁侧剥离破坏时的碳纤维表面位移(应变)的演化过程。实验还说明了电子散斑干涉技术不仅可用于位移的测量,而且也可用于结构安全监测和破坏预报。文中给出了对C20D、C25A和C60C侧贴碳纤维板加固在不同载荷作用直到构件破坏前的位移测试及对试件C60C轴线上的剪应力分析结果。     

PS溶液渗透对非饱和土的增强效应研究

特定模数硅酸钾溶液(PS)已广泛的用于我国西北干旱地区土遗址加固保护工程中,并且取得了显著的效果。但是PS对潮湿地区遗址土加固效果,目前尚缺乏成熟的理论和实验验证。本文从室内试验的资料出发,研究PS对潮湿地区土遗址非饱和土的增强效应。本次研究土样取自位于潮湿环境中的浙江杭州良渚土遗址(3000 B C.),在实验室内对高含水量(13％ ~25％)的重塑土样进行了PS渗透加固。通过研究对比加固前后重塑土样的固结特性和抗剪强度,发现 PS对潮湿地区遗址土也有一定的加固效果。加固效果随初始饱和度的不同而不同,但初始含水量达25%的土在PS作用下仍可能得到增强。经PS渗透的土样不仅提高了初始固结性能和抗剪强度,而且加固土样而且呈现出一定的弹脆性特征,呈现出塑脆性转化,表明PS渗透可能产生对土初始结构的稳固作用。这一探索研究将为扩大PS在土遗址加固保护工程的应用提供一定的理论支持。     

Passive solute separation in AC electroosmosis including surface charge-coupled hydrodynamic slip effects

Separation of electrically neutral, mutually noninteracting passive solutes via AC electroosmotic slit channel flows is investigated for general asymmetric wall surface zeta potentials and apparent hydrodynamic slip lengths. We consider the nontrivial coupling between the surface potentials (or charge densities) and the apparent slip lengths, and focus our attention on the occurrence of a so called “crossover phenomenon” for separating out the slow diffusers when both slow and fast diffusers are present. Results show that regardless of the potential-slip coupling, wider bandwidths become available for crossover phenomenon to occur when the electroosmotic velocity gradient (magnitude) is greater. Contrarily, plug-like velocity profiles inhibit crossover phenomenon, and the potential-slip parametric combinations leading to such profiles can be easily identified by the conditions for minimal transport enhancement reported in recent literature. When separating out the slow diffuser or crossover phenomenon is desired, we recommend incorporating significant asymmetry in the surface potential and apparent slip boundary conditions such that the operating frequency and flow oscillation amplitude may be lowered to more practical values. Our results also agree with and strengthen the physical picture for explaining crossover phenomenon in macroscopic pressure-driven oscillatory flows.     

固体相变过程中的宏细观力学问题及其研究进展

固体相变过程中的力学问题是近年来国际上固体力学与材料科学交叉领域中的一个研究热点,本文就作者在从事与相变有关的力学研究中所涉及到的问题以及国内外进展作一简述和展望,以引起国内学者的关注。