熔融挤出插层制备聚丙烯/蒙脱土纳米复合材料的探讨(Ⅰ)

通过双螺杆挤出机熔融挤出法制备出插层型聚丙烯/蒙脱土纳米复合材料。利用有机蒙脱土的预凝胶测试,复合材料的透射电子显微镜(TEM)观察,熔体流动指数测试(M I),力学性能测试,耐热性测试等方法进行了表征。结果表明,通过本方法制备的聚丙烯/蒙脱土复合材料是典型的插层型纳米复合材料。该复合材料在有机蒙脱土质量分数仅为4.0%时缺口冲击强度提高了103%,耐热性有所提高,而屈服强度、刚性基本不变,为研制PPR管等同时具有高韧性和高耐热性的聚丙烯产品开辟了一条崭新的途径。     

Beam wander and M2-factor of partially coherent electromagnetic hollow Gaussian beam propagating through non-Kolmogorov turbulence

Propagation formulae for M²-factor and beam wander of partially coherent electromagnetic hollow Gaussian (PCEHG) beam in non-Kolmogorov turbulence are derived based on the extended Huygens–Fresnel principle and the second-order moments of the Wigner distribution function. Our results indicate that the normalized M²-factors of PCEHG beam with larger beam order, waist width, inner scale of turbulence, the generalized exponent parameter, and smaller transverse coherent widths, outer scale of turbulence, the generalized structure parameter are less affected by the turbulence. The root mean square beam wander and relative beam wander are more obvious for PCEHG beam with smaller beam order, larger inner and outer scales of turbulence, exponent parameter, transverse coherent widths, and the generalized structure parameter. What is more, the beam wander properties of PCEHG beam in non-Kolmogorov turbulence are very different from M²-factor and spreading properties of beam in turbulence.     

Free vibration and stability of functionally graded circular cylindrical shells according to a 2D higher-order deformation theory

A two-dimensional (2D) higher-order deformation theory is presented for vibration and buckling problems of circular cylindrical shells made of functionally graded materials (FGMs). The modulus of elasticity of functionally graded (FG) shells is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. By using the method of power series expansion of continuous displacement components, a set of fundamental governing equations which can take into account the effects of both transverse shear and normal deformations, and rotatory inertia is derived through Hamilton’s principle. Several sets of truncated Mth order approximate theories are applied to solve the eigenvalue problems of simply supported FG circular cylindrical shells. In order to assure the accuracy of the present theory, convergence properties of the fundamental natural frequency for the fundamental mode r=s=1 are examined in detail. A comparison of the present natural frequencies of isotropic and FG shells is also made with previously published results. Critical buckling stresses of simply supported FG circular cylindrical shells subjected to axial stress are also obtained and a relation between the buckling stress and natural frequency is presented. The internal and external works are calculated and compared to prove the numerical accuracy of solutions. Modal transverse shear and normal stresses are calculated by integrating the three-dimensional (3D) equations of motion in the thickness direction satisfying the stress boundary conditions at the outer and inner surfaces. The 2D higher-order deformation theory has an advantage in the analysis of vibration and buckling problems of FG circular cylindrical shells.     

碳/蒙脱石复合材料的制备和表征

以蔗糖、蒙脱石为原料,在超声分散条件下,采用溶液插层、碳化方法制备插层型碳/蒙脱石纳米复合材料,通过X射线衍射(XRD)和红外光谱(FTIR)等分析表征方法对插层型蔗糖/蒙脱石纳米复合材料、碳/蒙脱石纳米复合材料进行表征,XRD结果表明,在400W的超声及70℃下,按蒙脱石:蔗糖:蒸馏水=1:2:20的比例超声反应2h,静置2h后能够得到d001=1.80nm的蔗糖/蒙脱石复合材料;将其在400℃氮气氛中碳化3h能够得到d001=1.34nm的复合材料。FTIR谱图表明,蔗糖/蒙脱石复合材料碳化完全,最终获得了具有三明治结构的碳/蒙脱石纳米复合材料。     

Controlled release formulation of ranitidine-containing montmorillonite and Eudragit® E-100

Aim: The objective of this work was to illustrate the suitability of montmorillonite (MMT) as a drug delivery carrier, by developing a new clay–drug composite of ranitidine hydrochloride (RT) intercalated in MMT. Methods: The MMT–RT composite was prepared by ion-exchange process. X-ray diffraction and Fourier transform infrared spectra were employed to confirm the intercalation of RT in the MMT interlayers. The prepared MMT–RT hybrid was coated with cationic polymer Eudragit® E-100 by oil-in-water solvent evaporation method. The release processes of RT from MMT–RT and MMT–RT/Eudragit® E-100 were monitored under in vitro condition in the gastric fluid. Results: X-ray diffraction and Fourier transform infrared spectra analysis indicated the intercalation of RT molecules within the clay lattice. The in vitro release studies showed that MMT–RT released RT in a controlled manner. In the case of MMT–RT/Eudragit® E-100, both the release rate and the release percentages noticeably increased in the presence of Eudragit® E-100, because of its effective exchange with intercalated RT molecules. The release kinetics followed parabolic diffusion mechanism. Conclusion: MMT has great potential as a drug delivery carrier with various scenarios. The dosage of the MMT–RT/Eudragit® E-100 can be in the tablet form. The hybrid material and polymer-coated hybrids are microparticles.     

Analysis of boundary-value problems describing the non-isothermal processes of elastoplastic deformation taking into account the loading history

We discuss the theory and approximate methods for solving boundary-value problems of thermoplasticity in a quasi-static formulation when the process of non-isothermal elastoplastic deformation of a body is a sequence of equilibrium states. In this case, the stress-strain state depends on the loading history, and the process of inelastic deformation is to be observed over the whole time interval being studied. The boundary-value problem is stated as a non-linear operator equation in the Hilbertian space. The conditions that provide the existence, uniqueness and continuous dependence of the generalized solution on the applied loads and initial strains are defined. A convergence of the methods of elastic solutions and variable elastic parameters is studied to solve the boundary-value problems describing the non-isothermal processes of active loading taking into account the initial strains dependent on the deformation history and heating. __________ Translated from Problemy Prochnosti, No. 1, pp. 69–99, January–February, 2006.     

A third-order triangular multilayered plate finite element with continuous interlaminar stresses

Based on a refined third-order shear deformation plate theory recently proposed by the author, a three-node, fully conforming, multilayered anisotropic plate element of arbitrary triangular shape is developed in this paper. The element incorporates 10 nodal d.o.f., namely the two in-plane displacements, the two shear rotations, the transverse displacement and its first and second derivatives, thus giving a total of 30 d.o.f. The formulation includes extension, bending and transverse shear deformation states; moreover, it fulfils a priori the geometric and stress continuity conditions at the interfaces, and it requires only five generalized displacements to describe the kinematics of the plate deformation. The formulated plate element is assessed for its performance comparing its predictions either with exact solutions from the plate model or with other approximate two-dimensional solutions.     

Tensile properties of melt intercalated polyamide 6 – Montmorillonite nanocomposites

The effects of montmorillonite (MMT) addition level on the tensile properties of PA6-MMT polymer-layered silicate nanocomposites (PLSN) were quantified using factorial experimental design (FED) to fit experimental data to a series of polynomial response-equations. Tensile behaviour, determined via FED, was related to the morphologies of the PLSN and compared to additional experimental data, determined for both a PLSN produced as a confirmation experiment and a PA6-MMT microcomposite of equivalent MMT content. In general, the PLSN displayed mechanical behaviour in keeping with their mixed exfoliated lamellae/intercalated lamellae-stack composite morphology and with the formation of a continuous phase of constrained polymer at an MMT loading of approximately 4 wt%. The data generated by the FED response-equation for tensile modulus were compared to the predictions of the Halpin–Tsai composite theory model. A modification to the Halpin–Tsai model was made in order to take account of changes in the distribution of the number (n) of lamellae in the stack particles. Using experimental data for n, the composite moduli of the PLSN were successfully modelled as summations of the contributions of each particle fraction of varying n.     

Studying nanostructure gradients in injection-molded polypropylene/montmorillonite composites by microbeam small-angle x-ray scattering

The core–shell structure in oriented cylindrical rods of polypropylene (PP) and nanoclay composites (NCs) from PP and montmorillonite (MMT) is studied by microbeam small-angle x-ray scattering (SAXS). The structure of neat PP is almost homogeneous across the rod showing regular semicrystalline stacks. In the NCs the discrete SAXS of arranged crystalline PP domains is limited to a skin zone of 300 μm thickness. Even there only frozen-in primary lamellae are detected. The core of the NCs is dominated by diffuse scattering from crystalline domains placed at random. The SAXS of the MMT flakes exhibits a complex skin–core gradient. Both the direction of the symmetry axis and the apparent perfection of flake-orientation are varying. Thus there is no local fiber symmetry, and the structure gradient cannot be reconstructed from a scan across the full rod. To overcome the problem the rods are machined. Scans across the residual webs are performed. For the first time webs have been carved out in two principal directions. Comparison of the corresponding two sets of SAXS patterns demonstrates the complexity of the MMT orientation. Close to the surface (< 1 mm) the flakes cling to the wall. The variation of the orientation distribution widths indicates the presence of both MMT flakes and grains. The grains have not been oriented in the flowing melt. An empirical equation is presented which describes the variation from skin to core of one component of the inclination angle of flake-shaped phyllosilicate filler particles.     

Analysis of Boundary-Value Problems of the Theory of Small Elastoplastic Strains,which Allows for Hydrostatic Stress and Stress Deviator Type

The author considers some versions of the deformation theory of plasticity, which takes into account the influence of hydrostatic stress and stress deviator type on the mechanical properties of a medium for the case of proportional loading. The emphasis is on the generalized statement of a nonlinear boundary-value problem and investigation of its solvability. Conditions have been determined that ensure the existence, uniqueness, and continuous dependence of the generalized solution on the loads applied.__________Translated from Problemy Prochnosti, No. 2, pp. 107 – 135, March – April, 2005     

薄壁箱梁剪力滞效应分析的初参数法

选取剪力滞效应引起的附加挠度作为广义位移,在定义新的剪力滞广义力矩及广义翘曲位移函数基础上,将薄壁箱梁的剪力滞变形状态从初等梁挠曲变形状态中分离出来作为一种独立的基本变形状态进行分析。对广义翘曲位移函数引入两个修正系数以充分考虑剪力滞翘曲应力的自平衡条件。提出了剪力滞翘曲应力的简便计算公式,它与初等梁弯曲应力公式具有相同的形式。用能量变分法建立了剪力滞控制微分方程,以广义力矩、广义剪力、附加挠度及其变化率作为四个初参数,给出了微分方程的初参数解。对两跨连续箱梁模型的应力计算表明:本文计算值与实测值及其它文献给出的计算值均吻合良好,从而验证了该文分析方法的正确性。挠度计算表明:剪力滞效应使该箱梁在集中荷载和均布荷载作用下的跨中挠度分别增大17%和16%。     

Multiscale modeling of polycrystalline silicon

Polycrystalline solid is composed of randomly distributed grains and grain boundaries. The size of grains is usually in the nano/micro-scale. In this paper, the general micromorphic theory, as well as a specialized micromorphic theory for covalent and ionic crystals, is introduced. A statistical model for polycrystalline material is adopted. Each grain is modeled as crystallized solid by micromorphic theory, while the grain boundaries are modeled as in its amorphous phase by classical continuum theory. Size-dependent material properties of silicon are investigated. Finite element analysis of thermomechanical coupling phenomenon in polycrystalline silicon is performed and numerical results are presented and discussed.     

A stable Galerkin reduced order model for coupled fluid–structure interaction problems

A stable reduced order model (ROM) of a linear fluid–structure interaction (FSI) problem involving linearized compressible inviscid flow over a flat linear von Kármán plate is developed. Separate stable ROMs for each of the fluid and the structure equations are derived. Both ROMs are built using the ‘continuous’ Galerkin projection approach, in which the continuous governing equations are projected onto the reduced basis modes in a continuous inner product. The mode shapes for the structure ROM are the eigenmodes of the governing (linear) plate equation. The fluid ROM basis is constructed via the proper orthogonal decomposition. For the linearized compressible Euler fluid equations, a symmetry transformation is required to obtain a stable formulation of the Galerkin projection step in the model reduction procedure. Stability of the Galerkin projection of the structure model in the standard L² inner product is shown. The fluid and structure ROMs are coupled through solid wall boundary conditions at the interface (plate) boundary. An a priori energy linear stability analysis of the coupled fluid/structure system is performed. It is shown that, under some physical assumptions about the flow field, the FSI ROM is linearly stable a priori if a stabilization term is added to the fluid pressure loading on the plate. The stability of the coupled ROM is studied in the context of a test problem of inviscid, supersonic flow past a thin, square, elastic rectangular panel that will undergo flutter once the non‐dimensional pressure parameter exceeds a certain threshold. This a posteriori stability analysis reveals that the FSI ROM can be numerically stable even without the addition of the aforementioned stabilization term. Moreover, the ROM constructed for this problem properly predicts the maintenance of stability below the flutter boundary and gives a reasonable prediction for the instability growth rate above the flutter boundary. Copyright © 2013 John Wiley & Sons, Ltd.     

Monotonous structure measures for social groups

The structure measure byKretschmer ¹ estimates the cooperation of a scientist. It is generalized in such a way that it increases with respect to the cooperation strengh with one of the collaborators. An alternative to the hierarchical structure measure is proposed which is continuous in all cooperation strengths.     

Three-dimensional finite element analysis of finite deformation micromorphic linear isotropic elasticity

A finite deformation micromorphic materially linear isotropic elastic model is formulated and implemented for three dimensional finite element analysis. The model is based on the kinematics, balance equations and thermodynamic equations proposed by Eringen and Suhubi (1964). The constitutive equations are calculated in the reference configuration, and the resulting stresses are mapped to the current configuration. The balance of linear momentum and the balance of first moment of momentum are linearized to construct the consistent tangent for three dimensional finite element implementation for solution by the Newton–Raphson method. Three dimensional numerical examples are analyzed to demonstrate preliminarily the implementation.     

多体非连续变形系统的计算力学模型及其应用

针对由不同特性物体所组成的多体系统,探讨了能够涵盖各种变形状态和运动形式的广义有限单元模式及其插值函数形式。对于多体接触问题,发展了能够合理描述界面特性的接触力元模型,即采用某种应力插值函数将界面上的相互作用力由接触对上的接触应力来表达,并将接触对上的接触应力当作需满足界面上屈服准则与流动法则等状态控制条件的参变量,将其作为约束条件加入系统控制方程。根据非连续变形系统的分区参变量最小势能变分原理,联立变分驻值条件与参变量的状态控制条件建立了多体系统非连续变形计算力学分析的基本控制方程,将问题最终归结为一个含有自由变量和等式约束条件的线性互补问题,对此发展了数值解法,并进行了多个算例的数值分析。计算结果表明该模型不仅能够对多体系统进行静、动力耦合分析,而且还能够模拟多体系统的变形与应力及接触界面上的接触应力和相对运动等复杂的非线性过程。     

Controlled synthesis of train-structured montmorillonite/layered double hydroxide nanocomposites by regulating the hydrolysis of polylactic acid

Two-dimensional nanosheets obtained by exfoliation can assemble into new functional nanomaterial. One of the critical challenges is developing an efficient method to make the layered composite complete exfoliation, and another is regulating and controlling nanosheets assembly to obtain the nanocomposite with specific structure. In this article, the platelets of layered double hydroxides (LDH) and montmorillonite (MMT) are exfoliated completely and efficiently in polylactic acid (PLA) by melting blend for 10 min, and the monolayers of MMT or LDH can store stably in PLA for a long time. A new well-organized layered nanocomposite containing the nanosheets of LDH and MMT was gained by being exfoliated and assembling. The structure of MMT/LDH nanocomposite not only holds a periodically alternating structure, but also possesses a train structure, and the formation mechanism of train structure is proposed at the first time; furthermore, the structure of MMT/LDH could be regulated and controlled. Fortunately, even being exfoliated and assembled, MMT nanosheet or LDH nanosheet was not destroyed. The MMT/LDH nanocomposite with expectant structure can be obtained by this efficient and environmentally friendly method, and this method may easily be extended to other layered materials.     

A microscopic theory of layered highT c superconductors

A generalized Gorkov formalism of superconductivity in a layered system with non-primitive lattice structure is given. This is used to justify theoretically a model of highT _c oxide superconductors proposed recently by one of us (SSJ). A numerical estimation of the critical temperature as a function of the number of superconducting layers is mentioned.     

聚乙烯醇/蒙脱土/山梨酸钾活性包装膜制备及释放

目的 通过制备聚乙烯醇（PVA）/蒙脱土（MMT）/山梨酸钾活性包装膜,考察其包装性能及山梨酸钾在膜材内的释放效果。方法 通过流延法制备含有不同浓度MMT的聚乙烯醇/山梨酸钾活性包装膜,分析活性包装膜的色度、透明度、拉伸性能和含水量,同时研究山酸钾在活性膜内向脂肪性食品模拟物中的释放行为。结果 通过添加MMT改善膜材的包装性能,MMT的添加在显著提高PVA膜拉伸强度的同时还降低了PVA膜的断裂伸长率,加深了膜材的色度,降低了膜的透明度;PVA膜的含水率随着MMT浓度的提高而降低。MMT的添加可明显改变山梨酸钾向脂肪类模拟物的释放行为,当MMT的质量分数为2%时明显地降低了山梨酸钾的释放量。结论 通过调整膜内MMT的浓度可以改变活性膜的色度、拉伸强度、含水量及膜内山梨酸钾的释放行为;使用Fickian第二定律模拟山梨酸钾释放是可靠的,可为山梨酸钾抗菌包装材料的进一步开发利用提供参考。