Methodology of physical mesomechanics as a basis for model construction in computer-aided design of materials

Conclusions The basic theses concerning the methodology of physical mesomechanics considered in this review show that a deformable solid can be represented as a microlevel system of self-consistent deformation structural elements of different scales. The law of scale invariance allows us to describe the behavior of very different materials under different loading conditions based on the element base for the scale levels of a deformable solid. The motion of volume structural elements of the deformation is described by the equations of mechanics (mesolevel and macrolevel), accommodation processes within the SEDs and on their boundaries — dislocation theory (microlevel). We have formulated an algorithm for construction of models for such multilevel systems which can be used in computer-aided design of materials. Examples of the classification of different structural materials have been presented based on the proposed algorithm.This work was done with the support of the Russian Foundation for Basic Research, Project No. 9301-16498.Institute of Physics of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 6–25, November, 1995.     

Integral method of nondestructive testing of optically transparent dielectric elements of band-pass filters

The narrow and wide band-pass filters with high electrical parameters both in the centimeter and millimeter wave band developed in the Microwave laboratory are built on the basis of H- and E-plane inserts made of a high Q dielectric monocrystal leukosapphire (tg 6*10^–6 in centimeter wave band). The filters based on the E-plane inserts have a rare spectrum of parasitic modes (up to doubled working frequency and higher) and those based on the H-plane inserts have lower insertion loss in the bandwidth. Fig.1 shows the design of a band-pass filter in which the resonators of both the first and second types are used to improve stability of amplitude-frequency characteristic in response to influence of production process and climatic factors. The electrodynamic calculation of such a filter electrical parameters is carried out according to the technique analogous to the one described in [1]. The prooedure of the band-pass filter manufacture envisages the operation of determining whether a specific dielectric element fits for pasting into the filter body. The most expedient testing method for filter elements is the electromagnetic resonance method. However, since the monocrystal leukosapphire is an anisotropic, opticallytransparent material [2], there exists a possibility of using not only the traditional SHF (Super High Frequency) method but also the method of optical testing of the quality of the dielectric element by the shape of conoscopic figures that enables to increase the output of suitable products with reduction of expenditure. A new approach to the nondestructive testing of optically-transparent filter elements using both methods and their mutual dependence in technological process, has been suggested.     

On the possibility of soft matter nanostructure formation based on mesoporous aluminum hydroxide. Prospects for biomedical applications

The effect of the nonequilibrium structure of 2D aluminum hydroxide-based objects on the macroscopic response (adsorption properties) is studied in the physical mesomechanics framework. Molecular dynamics simulation is performed to examine the nature of selective adsorption of the considered low-dimensional structures. The role of defects and structural elements, such as polar functional groups, is analyzed. Model ions and endotoxin are used to illustrate the selective character of adsorption. Prospects for biomedical applications of the obtained results are discussed.     

Antireflection fianite and ZrO<Subscript>2</Subscript> coatings for solar cells

Fianite is a promising multipurpose material for new electronic technologies owing to its unique combination of physical and chemical properties. It can be used in virtually all of the main technological stages of the production of micro-, opto-, and SHF-electronics; in particular, as a bulk dielectric substrate and a material for buffer layers in heteroepitaxy; as a material for insulating, antireflection, and protective layers in device elements; and as a gate dielectric [1–3]. In this work, we consider the possibilities for using fianite and ZrO₂ as an antireflection coating for silicon solar cells (SCs) and SCs based on InGaAsP heterostructures.     

辉光放电质谱法直接分析石墨中痕量杂质

石墨是理想的无机非金属材料,具有高化学稳定性、良好的导电性、较好的耐磨性等优点,被广泛应用于现代化学工业及其他诸多领域。由于石墨是难熔物,其中的微量杂质元素使用普通化学法或常规仪器分析法均难以准确检出。常用的火法-电感耦合等离子质谱(ICP)方法检测石墨存在的问题是：（1）在高温灼烧期间个别元素容易损失;（2）在加酸溶解灰化组分过程中部分杂质氧化物仍无法溶解完全。因此,很多学者开始研究利用固体进样法来测定石墨中的杂质元素含量。辉光放电质谱法（GDMS）是将辉光放电源（GD）与质谱分析方法（MS）联用的一种技术,采用固体进样方式,具有样品前处理简单、基体效应小、检出限低、灵敏度高等优点,在国内外已成为部分高纯金属和半导体材料分析领域的标准方法。灵敏度因子值(RSF)是一个用于校正GDMS分析结果的系数,对于GDMS分析而言,大部分元素在不同基体中仍然存在较明显的基体效应。要将GDMS分析作为一种定量分析方法,需要采用与基体匹配的标准物质来校正RSF,但目前大多数GDMS分析均采用仪器厂家提供的标准相对灵敏度因子（RSF_Std）进行测定,只能获得半定量分析结果。研究了采用GDMS直接测定石墨样品中9种杂质元素含量的方法,通过对放电条件等参数的优化选择,确定了石墨分析的最佳放电条件（电流强度为55 mA,放电气体流量为450 mL·min-1）。在此条件下采用半定量法（RSF_Std）测定了石墨参考样品中Mg,Cr,Ni,Ti,Fe,Cu,Al,Si,Ca共九种杂质元素含量,t检验结果表明,多数元素测量结果与参考值存在显著差异。要获得更为准确的结果,需要获得各元素相应的RSF_x以建立定量分析方法。通过实验,考察了不同的电流强度和放电气体流量对九种元素RSF值的影响,讨论了影响因素产生的原因。实验结果表明,电流强度和放电气体流量对大部分元素的RSF值都有较大的影响,其中放电气体流量对RSF值影响最大,各元素的RSF值变化幅度在15%和405%之间。在选定条件下采用RSF_x值定量分析了石墨材料中Mg,Cr和Ni等九种杂质元素含量,检测结果的t检验sig值均大于0.05,表明测定结果与参考值无显著性差异,方法的准确度有了显著提高;测定结果的精密度（RSD）介于3.2%～9.9%之间,方法可满足4N纯度以上高纯石墨材料的分析。     

Dynamic property analysis of the space-frame structure using the spectral element method

In this paper, the space-frame structure is analyzed using the spectral element method (SEM). It is periodic and composed of many geometrically uniform components. They can be considered as space beam-column elements. The spectral stiffness matrixes of the elements are established by using the variational method and the discrete Fourier transform theory. Then frequency responses of the structure are obtained by solving the spectral equations. In comparison with the results of the finite element method, those in the SEM are more accurate by taking less time, and the vibration bandgaps are observed from the responses of the structure. Moreover, the span, the substructure height, the substructure number, the material combination, the structural damping and the load location have obvious influences on the structural dynamic properties. These findings will provide the engineers with new ideas of the structural and the vibration isolation design.     

AN INVERSE EIGENVALUE FORMULATION FOR OPTIMIZING THE DYNAMIC BEHAVIOUR OF PIN-JOINTED STRUCTURES

An efficient relationship between geometric and material properties of pin-jointed truss structures and their eigenvalues is established. The problem is formulated as an inverse eigenvalue problem. This formulation allows the determination of the required modifications on the structural members to achieve specified eigenfrequencies. In addition to the modification of the existing structural elements, the formulation also allows addition of new structural elements to obtain the desired frequencies. Using the proposed inverse method, two cases of plane as well as space truss structures are studied and the results are compared with those obtained using the conventional optimization techniques adopted by commercial finite element codes.     

Analysis of wave propagation in a thin composite cylinder with periodic axial and ring stiffeners using periodic structure theory

Wave propagation characteristics of a thin composite cylinder stiffened by periodically spaced ring frames and axial stringers are investigated by an analytical method using periodic structure theory. It is used for calculating propagation constants in axial and circumferential directions of the cylindrical shell subject to a given circumferential mode or axial half-wave number. The propagation constants corresponding to several different circumferential modes and/or half-wave numbers are combined to determine the vibrational energy ratios between adjacent basic structural elements of the two-dimensional periodic structure. Vibration analyses to validate the theoretical development have been carried out on sufficiently detailed finite element model of the same dimension and configuration as the stiffened cylinder and very good agreement is obtained between the analytical and the dense finite element results. The effects of shell material properties and the length of each periodic element on the wave propagation characteristics are also examined based on the current analytical approach.     

Efficient parallel resolution of the simplified transport equations in mixed-dual formulation

A reactivity computation consists of computing the highest eigenvalue of a generalized eigenvalue problem, for which an inverse power algorithm is commonly used. Very fine modelizations are difficult to treat for our sequential solver, based on the simplified transport equations, in terms of memory consumption and computational time.A first implementation of a Lagrangian based domain decomposition method brings to a poor parallel efficiency because of an increase in the power iterations [1]. In order to obtain a high parallel efficiency, we improve the parallelization scheme by changing the location of the loop over the subdomains in the overall algorithm and by benefiting from the characteristics of the Raviart–Thomas finite element. The new parallel algorithm still allows us to locally adapt the numerical scheme (mesh, finite element order). However, it can be significantly optimized for the matching grid case. The good behavior of the new parallelization scheme is demonstrated for the matching grid case on several hundreds of nodes for computations based on a pin-by-pin discretization.     

Experimente mit dem neutronenspinecho mit langwelligen neutronen aus einem polarisierenden neutronenleiter

We describe an inexpensive method to obtain a highly polarized neutron beam of slow neutrons (λ = 1 – 15 Å) [1]. The high necessary field to saturate the applied soft magnetic material in the surface acting as a polarizing mirror indicates a behaviour of the magnetization in the surface different from that in the bulk material [2]. We also describe the realization of an apparatus proposed by F. Mezei [3], the behaviour of the polarized neutrons in this apparatus, and its use to get a spin echo with a neutron spectrum containing 3 – 9 Å wavelength neutrons. This spin echo is not destroyed by transmission through a nickel sheet, only the number of precessions is increased which appear in a displacement of the echo. This displacement can be used to measure the saturation magnetization of this sheet.     

Statistical estimate of the deformation of a light pulse in the location of plane stratified clouds

The study of clouds in the lower atmosphere by means of laser location (lidar) started in the second half of the sixties. The first investigations in this direction by Ligda [1] and Collis [2–5] indicated the extensive prospects of optical probe systems in studying the structure and dynamics of clouds. The powerful lasers used in these systems (lasers with pulses as short as 10^–9 sec) help in identifying the upper and lower boundaries and the spatial inhomogeneity of clouds of fairly low density with the resolution necessary for projector probing. As in the case of radar, methods of studying atmospheric objects with lidars are based on an analysis of the information included in the reflected signal. The reflected signal in these cases is formed by the back-scattering of light on diffuse interaction with atmospheric inhomogeneities. The different meteorological nature (shower, fog, haze, etc.) and internal structure of the inhomogeneities reflect differently on the parameters of the signal. In general the intensity, the state of polarization, the shape of the envelope of the pulse, and the energy and frequency spectrum all vary. However, the extraction and analysis of the information contained in these changes in order to solve the inverse problem present an extremely complicated problem, as yet only solved in individual simple cases. In problems relating to the laser probing of clouds and mists, one of the most informative and easily-analyzed characteristics is the degree of deformation of the initial pulse by reason of the repeated scattering of photons. A number of preliminary estimates establishing a relationship between the parameters of the cloud layer and the shape of the reflected light pulse were presented in [6–9]. In [6, 9], in particular, the authors estimated the time characteristics of a diffusely-reflected light signal by the method of statistical tests [10], which is particularly suitable for solving multidimensional problems of atmospheric optics [11]. The algorithm of the Monte Carlo method proposed in [6, 9] and used in the present investigation enables us to allow for the complicated boundary conditions arising in the propagation of a divergent, spatially-limited light beam in a layer-like inhomogeneous scattering medium, and also the transient nature of the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 50–53, February, 1973.     

A non-uniform basis order for the discontinuous Galerkin method of the 3D dissipative wave equation with perfectly matched layer

In this study a discontinuous Galerkin method (DG) for solving the three-dimensional time-dependent dissipative wave equation is investigated. In the case of unbounded problems, the perfectly matching layer (PML) is used to truncate the computational domain. The aim of this work is to investigate a simple selection method for choosing the basis order for elements in the computational mesh in order to obtain a predetermined error level. The selection method studied here relies on the error estimates provided by Ainsworth [M. Ainsworth, Dispersive and dissipative behaviour of high order discontinuous Galerkin finite element methods, Journal of Computational Physics 198(1) (2004) 106–130]. The performance of the non-uniform basis is examined using numerical experiments. In the simulated model problems, a feasible method choosing the basis order for arbitrary sized elements is achieved. In simulations, the effect of dissipation and the choices of the PML parameters on the performance of the DG method are also investigated.     

Dynamic cracking resistance of structural materials predicted from impact fracture of an aircraft alloy

A new approach to studying the dynamic strength properties of structural materials is demonstrated with fracture of 2024-T3 aircraft aluminum alloy. The central idea of this approach is the incubation time to failure. In [1], experimental data for dynamic fracture of this alloy were analyzed in terms of the classical fracture criterion, which is based on the principle of maximum critical stress intensity factor [2]. In [1], the dependence of the stress intensity factor limiting value (the dynamic fracture toughness K_Id, which was assumed to be a functional characteristic of the material) on the loading rate was also measured. The same experimental data were analyzed in terms of an alternative structure-time approach [3]. In this approach, the dynamic fracture toughness K_Id is considered as an estimable characteristic of the problem, so that determination of limiting loads does not require a priori knowledge of the loading-rate dependence of the dynamic fracture toughness. The incubation time to failure of the aircraft aluminum alloy is calculated. The difference in the loading-rate dependences of the dynamic fracture toughness, which is observed for various structural materials, is explained. The dynamic fracture toughness of the alloy under pulsed threshold loads is calculated.     

Evolution of substructures under microlevel and mesolevel plastic deformation

The existence of a hierarchy of structural levels of plastic deformation can be considered to be an experimentally and theoretically proven fact [1–3]. Mescheryakov [1] showed that a noncrytallographic level of deformation arises in elastoplastic waves, manifesting itself as macrofluxes of particles of the medium; the velocity of the particles relative to each other at velocity has dispersion and the particles move in the direction of the wave propagation. Displacement of macrofragments of the crystal, which is also a manifestation of noncrystallographic structural levels of deformation, has been detected in highly excited systems [2]. The relaxation approach used increasingly to describe plastic deformation assumes that defects are created, move, and are restructured during deformation in a way so that the level of stresses inside the material drops. The nonuniformity of the stress field gives rise to nonuniform plastic deformation and local shears and rotations at points of stress concentration. These concepts make it possible to use the principles of synergetics to build specific theoretical models and to consider loaded material as a nonequilibrum dissipative structure [3]. To date, however, the construction of the theory describing multilevel plastic deformation processes has not been completed. In particular, it is not yet known what levels are added, depending on the rate and duration of the loading and on how the levels are linked.St. Petersburg Branch of the A. A. Blagonravov Institute of Mechanical Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 7–12, October, 1992.     

Structural defects and device electrical behaviour in AlGaN/GaN heterostructures grown on 8° off-axis 4H-SiC

This paper reports on the influence of material defects on the electrical behaviour of AlGaN/GaN heterostructures grown onto off-axis 4H-SiC. A structural characterization revealed the presence of near-surface V-shaped defects, mostly oriented along the miscut direction [11-20]. High electron mobility transistors with the channel oriented along this direction showed a preferential conduction, while a significant reduction of the drain current occurred only along the orthogonal direction. An electrical analysis allowed us to demonstrate the anisotropy of the mobility of the two-dimensional electron gas.     

中低分辨率光谱的恒星Mg元素丰度估计方法研究

主要研究了一种新的基于ELM算法的中低分辨光谱的恒星Mg元素丰度估计方法。大科学工程郭守敬望远镜（LAMOST）为我们提供了海量的中低分辨率的光谱,确定这些光谱的Mg元素丰度将有助于我们深入了解银河系的形成历史和演化过程。目前从中低分辨率光谱中确定Mg元素丰度的方法主要是模板匹配法,但该方法算法复杂,优化参数较为困难且对噪声敏感,因此有必要研究新的方法。实验结果显示,ELM算法对MILES光谱的Mg丰度的估计的精度为0.009 9（0.15）dex,而对信噪比大于50的LAMOST光谱的精度为0.002 7（0.11）dex。通过与其他算法进行对比,证实ELM算法是一种能精确估计中低分辨率光谱的Mg元素丰度的算法,能够应用于LAMOST后期的光谱数据中。     

Tuneability amplification factor and loss of high-contrast composites

The problem of tuneability of nonlinear ferroelectric–dielectric composite materials is addressed. Attention is concentrated on the analysis of the tuneability amplification factor, K, of a composite material, which is introduced as the ratio of the effective tuneability of a composite material to the tuneability of its ferroelectric (tuneable) component. Previously, ferroelectric–dielectric composite materials have been designed with an effective tuneability amplification factor slightly greater than 1 (i.e. 1.1–1.4) [A.K. Tagantsev et al., J. Electroceramics 11 (2003) p.5; A.G. Kolpakov et al., J. Electroceramics 18 (2007) p.129]. It is demonstrated that the tuneability amplification factor can take values significantly greater than 1. Numerical prototypes (structural designs integrated with finite element method tools) of microstructures are presented with K in the range 3 to 30. The effective tuneability of nonlinear composite materials strongly depends on the microgeometry and microtopology of the material and, in general, cannot be described in terms of volume fraction of components of composite material. In the designs presented, the increased tuneability is due to concentration of the high electric field in narrow regions with carefully selected geometry. The problem of loss in ferroelectric–dielectric composite materials is discussed. In the general case, the loss tangent stays between that of the components of the composite. For high-contrast ferroelectric–dielectric composite materials, the effective loss tangent is practically equal to the loss tangent of the ferroelectric.     

非均匀材料的应变软化及叠层复合材料破坏过程的数值模拟

用有限元方法模拟了非均匀叠层材料的固体力学行为和破坏过程,各层材料性质的初始非均匀性采用某一给定的统计规则描述.用三维网格对试件进行有限元剖分,每个单元具有各自的均匀各向同性常量以反映总体的非均匀性.加载过程中不同单元破坏次序不同,因而整体等效应力应变关系表现出复杂的非线性性.通过数值计算,在选定的具体条件下,模拟了在逐步加载过程中,叠层材料应力应变场的变化和不同单元依次破坏直至试件整体破坏的过程.算例中叠层材料由14~15层构成,使用的网格数约为几千个.用该方法得到的非线性等效应力应变曲线与文[11,12]中叙述的拉伸作用下应变超过某一值后,材料发生应变软化现象的试验数据符合较好,趋势相当一致,因此可以设想是对应变软化原因的一种解释.     

Design, fabrication, and characterization of lightweight and broadband microwave absorbing structure reinforced by two dimensional composite lattice

Microwave absorbing structures (MASs) reinforced by two dimensional (2D) composite lattice elements have been designed and fabricated. The density of these MASs is lower than 0.5?g/cm³. Experimental measurements show that the sandwich structure with glass fiber reinforced composite (GFRC) lattice core can serve as a broadband MAS with its reflectivity below ?10?dB over the frequency range of 4?C18?GHz. The low permittivity GFRC is indicated to be the proper material for both the structural element of the core and the transparent face sheet. Calculations by the periodic moment method (PMM) demonstrate that the 2D Kagome lattice performs better for microwave absorbing than the square one at relatively low frequencies. The volume fraction and cell size of the structural element are also revealed to be key factors for microwave absorbing performance.     

Acoustical method for the determination of the elastic and piezoelectric constants of crystals of classes 6mm and 4mm

An acoustical method is proposed for the determination of the elastic and piezoelectric constants of crystals of classes 6mm and 4mm. The method is based on the technique developed for orthorhombic crystals of class mm2 and described in the previous paper [9]. Only three samples are required for the determination of all elastic and piezoelectric constants of crystals belonging to the two symmetry classes of interest; for the crystals of class 6mm, only two samples are necessary. The proposed method can be used only when the signs of the piezoelectric constants are known beforehand. Knowing the sign of electrostriction for the crystals under study, the relative signs of the piezoelectric constants can be uniquely determined in accordance with the data reported earlier [10]. This approach allows one to extend the method used in the previous paper [9] to crystals of classes 6mm and 4mm.