A two-scale method for identifying mechanical parameters of composite materials with periodic configuration

In this paper, a two-scale method （TSM） is presented for identifying the mechanics parameters such as stiffness and strength of composite materials with small periodic configuration. Firstly, a formulation is briefly given for two-scale analysis （TSA） of the composite materials. And then a two-scale computation formulation of strains and stresses is developed by displacement solution with orthotropic material coefficients for three kinds of such composites structures, i.e., the tension column with a square cross section, the bending cantilever with a rectangular cross section and the torsion column with a circle cross section. The strength formulas for the three kinds of structures are derived and the TSM procedure is discussed. Finally the numerical results of stiffness and strength are presented and compared with experimental data. It shows that the TSM method in this paper is feasible and valid for predicting both the stiffness and the strength of the composite materials with periodic configuration.

Computational multiscale methods for granular materials

The fine-scale heterogeneity of granular material is characterized by its polydisperse microstructure with randomness and no periodicity. To predict the mechanical response of the material as the microstructure evolves, it is demonstrated to develop computational multiscale methods using discrete particle assembly-Cosserat continuum modeling in micro- and macro- scales,respectively. The computational homogenization method and the bridge scale method along the concurrent scale linking approach are briefly introduced. Based on the weak form of the Hu-Washizu variational principle, the mixed finite element procedure of gradient Cosserat continuum in the frame of the second-order homogenization scheme is developed. The meso-mechanically informed anisotropic damage of effective Cosserat continuum is characterized and identified and the microscopic mechanisms of macroscopic damage phenomenon are revealed. c 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi： 10.1063/2.1301101]

Second-order two-scale computational method for ageing linear viscoelastic problem in composite materials with periodic structure

The correspondence principle is an important mathematical technique to compute the non-ageing linear viscoelastic problem as it allows to take advantage of the computational methods originally developed for the elastic case. However, the correspon- dence principle becomes invalid when the materials exhibit ageing. To deal with this problem, a second-order two-scale （SOTS） computational method in the time domain is presented to predict the ageing linear viscoelastic performance of composite materials with a periodic structure. First, in the time domain, the SOTS formulation for calcu- lating the effective relaxation modulus and displacement approximate solutions of the ageing viscoelastic problem is formally derived. Error estimates of the displacement ap- proximate solutions for SOTS method are then given. Numerical results obtained by the SOTS method are shown and compared with those by the finite element method in a very fine mesh. Both the analytical and numerical results show that the SOTS computational method is feasible and efficient to predict the ageing linear viscoelastic performance of composite materials with a periodic structure.

Second-order two-scale computations for conductive radiative heat transfer problem in periodic porous materials

In this paper, a kind of second-order two-scale （SOTS） computation is developed for conductive-radiative heat trans- fer problem in periodic porous materials. First of all, by the asymptotic expansion of the temperature field, the cell problem, homogenization problem, and second-order correctors are obtained successively. Then, the corresponding finite element al- gorithms are proposed. Finally, some numerical results are presented and compared with theoretical results. The numerical results of the proposed algorithm conform with those of the FE algorithm well, demonstrating the accuracy of the present method and its potential applications in thermal engineering of porous materials.

Statistical second-order two-scale analysis and computation for heat conduction problem with radiation boundary condition in porous materials

This paper discusses a statistical second-order two-scale（SSOTS） analysis and computation for a heat conduction problem with a radiation boundary condition in random porous materials.Firstly,the microscopic configuration for the structure with random distribution is briefly characterized.Secondly,the SSOTS formulae for computing the heat transfer problem are derived successively by means of the construction way for each cell.Then,the statistical prediction algorithm based on the proposed two-scale model is described in detail.Finally,some numerical experiments are proposed,which show that the SSOTS method developed in this paper is effective for predicting the heat transfer performance of porous materials and demonstrating its significant applications in actual engineering computation.

Multi-scale modeling in microstructure evolution of materials

Intelligent design and control of the microstructure to tailor properties of materials is the dream that materials scientists have been worked hard for many years. Formation of research area of computational materials science paves the way to realize the dream. Simulation of microstructure evolution is a chief branch of the computational materials science and has caused great attention from materials researchers. Multi-scale modeling gets popular just within 5-6 years recently due to huge research works to try to shorten the distance between simulation and application. People have to command one or more classical simulation methods in order to do the multi-scale modeling so chief simulation methods will be discussed first and then more reviews in detail are given to the phase field simulation. The main part of the paper is carried out to introduce two key approaches to do the multi-scale modeling job. It is suggested that extension of the multiscale modeling is necessary to study the technologies to link microstructure simulation, processing simulation and property simulation each other as well as to build bridges between different simulation methods and between analytical models and numerical models.

Multiple structure graphite stabilized stearic acid as composite phase change materials for thermal energy storage

This paper used 3 types of graphite with different physical structures as the porous matrix to prepare composite phase change materials(PCMs),and investigated their photo-thermal conversion performance and application in battery thermal management.Multiple structure graphite minerals,including microcrystalline graphite(MG),scale graphite(SG),and expanded graphite(EG)were used as porous matrix,while stearic acid(SA)acts as the phase change material.The vacuum impregnation method was applied to prepare SA/MG,SA/SG,SA/EG,and SA/MG1,and SA/EG1was/were prepared by the ethyl alcohol method.Results show that the thermal conductivities of all composite phase change materials were 10.82 to 22.06 times higher than that of the pure SA.Thermogravimetric(TG)analysis showed that the loadages of SA were 43.61%,18.74%,and 92.66%for SA/MG,SA/SG,and SA/EG respectively.The load rates of SA were 18.98%and 18.88%for SA/MG1 and SA/EG1,respectively.For the 3 types of graphite materials of different dimensions,the BET(Brunauer,Emmett,and Teller)surface area determines the maximum load of SA.The Fourier-transform infrared(FTIR)and X-ray diffraction(XRD)results indicated that there was good compatibility between the SA and the supports.The SA/EG1 has better thermophysical properties in heat energy storage and release process.The thermal infrared images show that SA/EG1 has higher sensitivity to the temperature changes.SA/EG1 has better photo-heat conversion performance than SA/SG and SA/MG1 attributed to the multilayer structure of EG.SA/EG has better thermal management performance in the Li-ion batteries discharge process.

THE ANTI-PLANE SHEAR FIELD IN AN INFINITE SLAB OF ELASTO-DAMAGED MATERIAL WITH A SEMI-INFINITE CRACK

This paper deals with an infinite slab with a semi-infinite crack,which is subjected to the anti-plane shear k_Ⅲ field at infinity.The slab is made of an elasto-damaged material.Analytical solution is obtained by use of conformal mapping.The shape of damaged-zone,the dissipative energy,the shear open- ing displacement on the crack surface and several stress distribution curves are given.The far field condition is checked,The asymptotic behavior near the crack-tip is given.

Sustainable Intensification of Cultivated Land Use and Its Influencing Factors at the Farming Household Scale: A Case Study of Shandong Province, China

Promoting the sustainable intensification of cultivated land use(SICL) has become crucial for ensuring a sufficient supply of grain and important agricultural products, as well as for the sustainable use of resources. Taking widely used areas of Shandong Province in China as examples, an analytical scale and level framework for SICL is constructed in this study. It measures the level of SICL through material flow analysis, constructs Tobit models to analyze the influencing factors of SICL at the farming household scale,and analyzes the transition mechanisms of SICL. The results show that the overall level of SICL in Shandong Province is low, and the spatial distribution is uneven. There are relatively more farmers participating in unsustainable intensification than in medium or low levels of SICL, with farmers working at a high level of SICL making up the smallest proportion. The factors that determine the level of SICL at which farmers work vary significantly. More male farmers operate at a low SICL level than female farmers, while females outnumber males at a high SICL level. This is mainly related to the regional distribution of age and population. Meanwhile, with larger cultivated land areas, there is a lower degree of land fragmentation, with a higher level of SICL corresponding to a smaller distance to the nearest town closer within 1–5 km from the town center. We can see the level of SICL and its processes themselves are closely related to time and space scales. Based on the above analysis, it is necessary to clarify the standard processes of SICL to adapt them to local conditions. This includes instructing managers on how to improve resource utilization, increase the sustainable development of cultivated land and establish a comprehensively efficient and functional SICL mechanism. The sustainable intensification of cultivated land use and its specific application in the new era are conducive to enriching the frontier theories and methodology of sustainable development, and are of great significance to the advancement of green agriculture and the decision-making of rural high-quality development.

Bioinspired fish-scale-like magnesium composites strengthened by contextures of continuous titanium fibers:Lessons from nature

Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers.The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures.In particular,the double-Bouligand architecture can effectively deflect cracking paths,alleviate strain localization,and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite,representing a successful implementation of the property-optimizing mechanisms in fish scales.The strength of the composites,specifically the effect of their bioinspired architectures,was interpreted based on the adaptation of classical laminate theory.This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.

Measurement of length-scale and solution of cantilever beam in couple stress elasto-plasticity

Owing to the absence of proper analytical solution of cantilever beams for couple stress/strain gradient elasto-plastic theory, experimental studies of the cantilever beam in the micro-scale are not suitable for the determination of material length-scale. Based on the couple stress elasto-plasticity, an analytical solution of thin cantilever beams is firstly presented, and the solution can be regarded as an extension of the elastic and rigid-plastic solutions of pure bending beam. A comparison with numerical results shows that the current analytical solution is reliable for the case of σ0 〈〈 H 〈〈 E, where σ0 is the initial yield strength, H is the hardening modulus and E is the elastic modulus. Fortunately, the above mentioned condition can be satisfied for many metal materials, and thus the solution can be used to determine the material length-scale of micro-structures in conjunction with the experiment of cantilever beams in the micro-scale.

The Microwave Synthesis and Photo-catalytic Activity of SnO_2·TiO_2 Nano-composite

A microwave-assisted heating approach was developed to fabricate SnO2·TiO2 nano-composite in an aqueoas sohaion of sulphuric acid in the presence of SnO2 nano-powder and titanium sulfate. Powder X-ray diffraction （ XRD ） pattern indicates that the products were a composite with both of anatase-type TiO2 and tetrahedrul SnO2. The prnducts were also characterized by transmission electron microscolry （ TEM ）, photoluminescence （PL） spectra. The photo-catalytic property of the as-prepared sample has ulso been studied. The result indicates that the as-prepared sample is a good photo-catadyst.

MULTI-SCALE AND MULTI-PHASE NANOCOMPOSITE CERAMIC TOOLS AND CUTTING PERFORMANCE

An advanced ceramic cutting tool material Al2O3/TiC/TiN （LTN） is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC （LZ） ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.

隧道突涌水灾害缩尺物理模型试验研究综述

随着我国经济的快速发展,隧道工程建设越来越多地面临着大埋深、高地应力、高地温、高渗透压力等复杂地质环境,运用物理模型试验开展复杂环境下隧道突涌水灾变机理与安全防控研究已成为岩石力学的热点问题。结合近年来国内外针对隧道突涌水灾变缩尺物理模型试验开展的研究工作,重点对该类物理模型的流固耦合相似理论、相似材料研制、渗透压加载方法等内容进行了系统梳理,并对下一步的可能发展方向进行展望。参考部分文献和突水典型案例后,总结了流固耦合相似准则和高地应力下的相似准则、相似材料选用方案及材料配比、试验中的水压加载方案,认为未来关注的重点包括考虑温度场的物理模型试验相似准则的研究和涌水涌泥与突水突泥间渐变过程的研究2个方面。

空气过滤用静电纺纳米纤维材料研究进展

面对日益严重的空气污染,传统过滤材料的过滤效率低且过滤阻力大,静电纺纳米纤维材料具有高孔隙率、大比表面积等特性,过滤效率高且过滤阻力小,可广泛应用于空气过滤及个人防护等领域。为此,首先从加工方式方面综述了3种静电纺丝法,不同的方法可获得不同尺度的纤维;其次,从不同纳米纤维材料结构和功能化制备角度,系统综述了空气过滤纳米纤维材料的最新研究进展;最后对规模化制备及纺丝原理进行论述,并展望了未来发展趋势。研究认为:需要深入研究静电纺丝机制,进一步研究电场、溶液、纤维成形之间的影响机制与构效关系开发新技术,来实现静电纺纳米纤维材料的规模化宏量制备;在此基础上对其进行功能化改进,研发具备自清洁、抗菌和传感等功能的空气过滤纳米纤维材料,以提高其在空气过滤领域的应用价值。

基于多维标度和聚类分析的“物质结构和性质”模块情境素材分类研究

不同类别情境素材具有不同的教学功能.在“物质结构与性质”模块教学中,合理选用情境素材能促进学生理解与辨析、逻辑与推理等能力的培养.为系统探察“物质结构与性质”模块情境素材的类别,以课程标准和人教版选择性必修2为源,通过文本研究法和问卷调查法筛选出35个情境素材.以中学化学一线教师以及某师范大学本科生、研究生为研究对象,通过系统聚类法确定情境素材的类别.研究发现,“物质结构和性质”模块情境素材分为社会生活、学术探究、科技前沿、模拟联想、科学史实、实验探索6类.研究可为学者和一线教师高效开展情境教学研究与实践提供参考.

两尺度视角下准脆性材料的损伤:从几何不连续度到自由能折减

多尺度损伤演化法则的构建是损伤力学从现象学走向理性坚实基础的核心之一.然而,迄今鲜有人注意到,存在两类损伤变量:几何意义上表征材料不连续程度的损伤与自由能折减(即材料受力性能退化)意义上的损伤.如何实现从几何意义上的损伤向能量耗散意义上的损伤转化,乃是固体破坏问题的枢机.本文从两尺度视角给出了损伤演化法则及几何意义上的损伤向能量耗散(即受力性能的退化)转化过程的定量刻画,进一步夯实了非局部宏-微观损伤模型的理性基础.在本文模型中,连续体被看作物质点的集合.宏观物质点与其作用域中的其他物质点组成一系列物质点偶,由此形成附加于其上的细观结构.在外部载荷作用下,物质点的位移引起物质点偶的变形.当物质点偶的某种几何变形量(如正伸长量)超过临界值时,微细观损伤开始发展.细观层次物质点偶的渐进破坏引起宏观固体不连续程度的变化,最终导致宏观连续体拓扑的改变.因此,将微细观损伤在作用域中的累积定义为该点的拓扑损伤,以刻画宏观固体的不连续程度,这在本质上是几何意义上的损伤.另一方面,损伤发展引起自由能耗散,导致连续体力学性能的退化.由于宏观能量耗散是作用域中细观物质点偶因损伤而导致的耗散能量之和,因此能量(受力)意义上的损伤为作用域中细观物质点偶上的总耗能与总弹性自由能之比.由此,在细观层次上实现了从几何意义上的损伤向能量耗散(受力退化)意义上的损伤的转化.在本文模型中,不需要经典连续介质损伤力学或断裂相场模型中经验假定的能量退化函数,物质点处的几何-能量转绎关系由该点的两尺度变形状态决定,而非固定形式,从而可能对复杂受力状态具有更好的适应性.计算结果表明,模型不仅可以捕捉到裂纹萌生、扩展全过程,而且可以定量反映加载过程中的载荷-位移曲线.与在宏观层次进行几何-能量转绎的宏-微观损伤模型相比,本文模型可以更准确地捕捉到试验结果的细节.

磁电弹性材料含正六边形纳米缺陷的表面效应研究

在磁电弹性材料断裂力学框架下,利用表面弹性理论和解析函数边值理论,解析研究了反平面机械载荷、面内电载荷和磁载荷耦合作用下磁电弹性体中正六边形孔边均布六条等长裂纹的Ⅲ型断裂力学问题,确定了考虑表面效应时纳米尺寸裂纹问题的精确解.基于以上解析解,通过数值算例揭示了表面效应、缺陷几何参数及所施加的损坏载荷分别在两种理想裂纹面电磁条件假设下对断裂参数的影响规律.研究发现:考虑表面效应时影响裂纹扩展的因素与经典弹性理论解答明显不同.各个物理分量呈现出显著的尺寸依赖效应,但随着缺陷尺寸的增加,表面效应的影响呈下降趋势,并趋于经典弹性理论值.研究可为该材料应用于微纳米结构和微机电系统提供理论指导.

铁路钢桁梁桥明桥面复合轨枕宏-细观力学行为研究

复合轨枕是明桥面结构提质改造的重要举施,但复合成型工艺及材料特性对轨枕服役性能有直接影响。针对复合轨枕明桥面结构的特性,基于ABAQUS等仿真平台,分别建立复合轨枕的宏、细观有限元模型,从多尺度仿真角度研究列车轮载下复合材料密度,纤维束直径、取向和分布等因素对轨枕承载能力及变形影响。结果表明:增大纤维束直径、使纤维束充分分散,能够减少10%~30%的轨枕受力;改变纤维取向对提高轨枕承载力的效果较为显著,优化纤维分布取向能够使轨枕表面受力减小20%~30%;在此基础上提出“45°/0°/45°”的纤维束铺层结构,采用这种结构能在相同变形量控制水平下获得更高的承载能力,较全断面纵向铺层方案提升30%~50%。研究表明:利用复合轨枕的材料特性,优化生产制造工艺可提高其承载能力。

船用复合材料螺旋桨稳态流固耦合尺度效应数值研究

为实现实尺度复合材料螺旋桨的流固耦合性能预报,针对船用复合材料螺旋桨在均匀流场中稳态流固耦合的尺度效应问题,本文基于Ansys Workbench建立了双向流固耦合算法,采用ACP模块对3种尺度的4381复合材料螺旋桨进行30°角铺层建模,分析了流固耦合下结构变形与敞水性能变化的尺度效应规律。研究结果表明:粘性力相对占比是刚性桨敞水性能尺度效应的主要因素;流固耦合最大变形比和螺距变形比均与缩尺比呈线性关系,因流体的附加刚度作用,最大变形比需在悬臂板挠度公式基础上作3%的修正;流固耦合后敞水性能的改变量与缩尺比呈线性关系,其尺度效应需在刚性桨敞水性能尺度效应关系上进一步作5%~7%的修正,修正量与复材桨压力中心区和桨叶的厚度均有一定关系。考虑流固耦合的复材桨尺度效应修正为不同尺度复材桨的数值计算和性能预报提供了有效参考。