不同尺度分布散粒材料砂堆形成过程的二维离散元模拟

用作者开发的离散元程序,模拟不同尺寸分布的砂堆形成过程。把散体颗粒简化为圆形颗粒,模拟过程分三步:首先利用参考网格生成颗粒的松散堆积结构;为了避免颗粒下落的冲击作用对砂堆安息角的影响,先模拟颗粒在重力作用下在圆柱容器内的自由下落与堆积,直至堆积达到稳定;最后,移除容器,只保留一个底部边界,模拟颗粒体系的散落过程,直至形成一个稳定的砂堆。模拟结果表明,在其他参数保持相同的情况下,随着颗粒尺寸的减小,砂堆的安息角逐步减小并趋向于一常值。对模拟中的两组颗粒体系进行相同条件下的砂堆形成实验,结果表明,模拟与实验所得安息角大体相当。

散粒材料压缩模量修正及群桩基础稳定性研究

天然沉积土在上覆土层重力作用下完成固结,其压缩模量大小和土层所受的前期固结压力大小直接相关。首先,分析岩土材料本构关系的主要影响因素,建立考虑模量随深度和体积应变变化的本构关系式;其次,建立桩基础稳定性问题的有限元求解格式,考虑水平荷载和下游冲刷深度对多种工况进行数值模拟分析;最后,根据计算结果,分析下游冲刷和水平荷载作用形成不对称接触边界对不同平面位置基桩受力特点,分析应力集中产生的原因及折屈失稳和整体稳定性问题。研究结果可为复杂大型工程群桩基础设计考虑桩、土及承台共同协调作用提供定量计算方法。

柔性散粒材料隔爆性能实验研究

为战场人员及精密仪器设备提供有效防护炸弹爆炸冲击波震动危害的优质作战防护装备器材,是当前作战防护装备研究的重点。选择具有高效吸收爆炸能量的柔性散粒材料进行实验研究,分析对比其材料性质及动力学特性,以便为研发有效应对现代常规炸弹爆炸防护的优质防护器材提供有效支持。

柔性散粒材料静力及动力学性能实验研究

战场环境下单兵防常规炸弹爆炸抗震减震技术装备及器材,由于受经费投入、战场环境等因素影响,一直没有成功研制并得到装备。通过室内砂箱振动台震动模拟试验,测试了不同柔性散粒材料在震动条件下的加速度值,对其减震性能作了一些初步的探讨。通过研究,可以看到柔性散粒材料在隔震方面具有其他材料所不具有的优越性能,可以作为制造隔震器材的首选。

散粒体防水材料的防水机理

通过对散粒体防水材料防水机理的讨论，证明了其防水机理在于反毛细管压力，从而在理论方面论证了其可靠性．

煤矸石散粒料的分形特征研究

应用分形几何理论对徐州地区的煤矸石散粒料进行了粒度分析 ,并研究了几个矿区煤矸石散粒料的粒度分布的分维 ,研究表明煤矸石散粒料具有分形结构特征 ,散粒材料的粒度级配特征参数———不均匀系数Cu=61 /( 3-D) 、曲率系数Cc=1 .5 1 /( 3-D) 。

中主应力对散粒体材料强度和变形影响的数值模拟研究

采用PFC3D数值模拟软件,研究散粒体材料在真三轴试验条件下中主应力对强度和变形的影响,并用统计方法从细观角度探讨中主应力的影响机制。数值模拟结果表明,中主应力比b增大,材料的有效内摩擦角、轴向应力峰值以及对应的轴向应变都呈现先增大然后减小的变化规律。b值的增大使中主应力方向应变由拉伸变为压缩,体应变由剪缩变为剪胀。b值对散粒体材料有效内摩擦角的影响规律和Lade-Duncan准则比较一致。从细观层面上,b值影响颗粒间法向接触力的分布。在b值增大过程中,当b值较小时中主应力方向的增强效应占主导使得材料强度增大,b值较大时小主应力方向的减弱效应占主导使得材料强度降低。

道路工程中碎石散粒体材料极限二次松散系数试验研究

研究了碎石散粒体材料极限二次松散系数的测定方法并设计了测试装置。试验分析了不同粒径、颗粒形状、不同含水率、含泥量及级配对散粒体材料极限二次松散系数的影响。试验表明,随着碎石散粒体材料粒径的增大,极限二次松散系数呈现先增大后减小的趋势,且相同粒径的碎石相比卵石具有更好的松散能力。随着含水率的增大,碎石散粒体材料的极限二次松散系数先下降后增加。含泥量对碎石散粒体材料的影响很大,尤其是对于小粒径的碎石散粒体材料。级配碎石散粒体材料的松散性较单一粒径的松散性差。

建筑垃圾资源化利用新技术及产业链构思

本文从建筑垃圾的基本概念入手,阐明了建筑垃圾的资源化利用的重大意义、国内外建筑垃圾的处理利用现状,以及从现有处理利用产品系列到房屋和道路的地基基础工程应用的新技术,并对建筑垃圾处理产业链问题加以深入思考,展现了建筑垃圾的资源化利用的广阔前景。

Discrete numerical modeling of granular materials considering crushability

The aim of this study is to numerically investigate the influence of particle breakage on the mechanical behavior of granular materials using a discrete element method(DEM). To enable particle crushing, non-crushable elementary particles are boned together to represents the granular aggregates which can be crushed when the external force exceeds its strength. The flaw of the aggregate was also modeled by randomly distributed void. Single particle crushing tests were carried out to determine the distribution of particle strength. The results of single particle crushing tests illustrate that the simulated single particle fracture strength and pattern agree well with the Weibull's distribution equation.Conventional oedometer tests, drained monotonic and cyclic triaxial tests were also carried out to investigate the crushing of the aggregates and the associated mechanical behaviors. The effect of confining pressure on the crushing of aggregates and the mechanical behavior was also analyzed. It was found that the peak stress and dilation decrease significantly when particle crushing was considered.The deformation behavior of the specimen is essentially controlled by two factors: particle rearrangement-induced dilation and particle crushing-induced contraction. The increase of permanent strain and the reduction of dilation were observed during cyclic loading and they tend to reach a stable state after a certain number of cycles. The crushing of aggregate is most significant in the first two cycles. The results also indicated that for the same axial strain the volumetric strain and the bound breakage in the cyclic loading tests are significantly larger than that in the monotonic loading tests,especially at high cyclic stress ratio.

Preparation of nano-structured Ag solid materials and application to surface-enhanced Raman scattering

Silver nano-particles with average diameter of about 60 nm were compacted in a high-strength mold under different pressures at 523 K to produce nano-structured Ag solid materials. The structure and characteristic of the nano-structured Ag solid materials (NSS-Ag) were studied using X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectrometer. The NSS-Ag could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. The common probe molecules Rhodamine 6G (R6G, 1×10-10 mol/L) were used to test the SERS activity on these substrates at very low concentrations. It is found that the SERS enhancement ability is dependent on the density of NSS-Ag. When the relative density of NSS-Ag is 83.87%, the materials reveal great SERS signal.

Size Control of Nanoscale Silicon Particles Formed in Thermally Annealed A-Si∶H Films and Its Photoluminescence

A method to control the size of nanoscale silicon grown in thermally annealed hydrogenated amorphous silicon （a-Si：H） films is reported. Using the characterizing techniques of micro-Raman scattering, X-ray diffraction and computer simulation, it is found that the sizes of the formed silicon particles change with the temperature rising rate in thermally annealing the a-Si ： H films. When the a-Si：H films have been annealed with high rising rate（～100℃/s）, the sizes of nanoscale silicon particles are in the range of 1.6～15nm. On the other hand, if the a-Si：H films have been annealed with low temperature rising rate（～1℃/s）, the sizes of nanoscale silicon particles are in the range of 23～46nm. Based on the theory of crystal nucleation and growth, the effect of temperature rising rate on the sizes of the formed silicon particles is discussed. Under high power laser irradiation, in situ nanocrystallization and subsequent nc-Si clusters are small enough for visible light emission, authors have not detected any visible photoluminescence（PL） from these nc-Si clusters before surface passivation. After electrochemical oxidization in hydrofluoric acid, however, intense red PL has been detected. Cyclic hydrofluoric oxidization and air exposure can cause subsequent blue shift in the red emission. The importance of surface passivation and quantum confinement in the visible emissions has been discussed.

True triaxial behavior of sandy soils under both drained and undrained conditions:A discrete element perspective

An advanced discrete element servomechanism that can simultaneously and independently control the evolution equations of six stress and strain components without introducing severe stress concentration is implemented.Such a comprehensive series of discrete element method simulations of both drained and undrained behavior of transversely isotropic sandy soils are successfully conducted in the true triaxial setting.During the simulation process,the evolution patterns of the load-bearing structure of the granular specimen are tracked using a contact-normal-based fabric tensor.The simulation results show that sandy soils exhibit more significant non-coaxiality between the loading direction and the major principal direction of the fabric tensor under extension than under compression.Therefore,the fabric of the sandy soils under extension has a stronger tendency to evolve toward the loading direction than that under compression,causing a more significant disturbance to the load-bearing structure.Consequently,compared with the extension loading condition,the transversely isotropic specimen under compression exhibits a higher shear strength and stronger dilatancy under drained conditions and a stronger liquefaction resistance under undrained conditions.

Preparation of carbon-coated iron oxide nanoparticles dispersed on graphene sheets and applications as advanced anode materials for lithium-ion batteries

We report a novel chemical vapor deposition （CVD） based strategy to synthesize carbon-coated Fe203 nanoparticles dispersed on graphene sheets （Fe2Og@C@G）. Graphene sheets with high surface area and aspect ratio are chosen as space restrictor to prevent the sintering and aggregation of nanoparticles during high temperature treatments （800 ℃）. In the resulting nanocomposite, each individual Fe2O3 nanoparticle （5 to 20 nm in diameter） is uniformly coated with a continuous and thin （two to five layers） graphitic carbon shell. Further, the core-shell nanoparticles are evenly distributed on graphene sheets. When used as anode materials for lithium ion batteries, the conductive-additive-free Fe2OB@C@G electrode shows outstanding Li＋ storage properties with large reversible specific capacity （864 mAh/g after 100 cycles）, excellent cyclic stability （120% retention after 100 cycles at 100 mA/g）, high Coulombic efficiency （-99%）, and good rate capability.

Magneto-enhanced electro-thermal conversion performance

Synergistically regulating carrier and phonon transport on the nanoscale is extremely difficult for all thermoelectric(TE)materials without cage structures.Herein BaFe_(12)O_(19)/Bi_(2)Te_(2.5)Se_(0.5)thermoelectromagnetic nanocomposites are designed and synthesized as a benchmarking example to simultaneously tailor the transport properties on the nanoscale.A magneto-trapped carrier effect induced by BaFe_(12)O_(19)hard-magnetic nanoparticles(NPs)is discovered,which can lower the carrier concentration of n-type Bi_(2)Te_(2.5)Se_(0.5)matrix by 16%,and increase the Seebeck coefficient by 16%.Meanwhile,BaFe_(12)O_(19)NPs provide phonon scattering centers and reduce the thermal conductivity by 12%.As a result,the ZT value of the nanocomposites is enhanced by more than 25%in the range of 300-450 K,and the cooling temperature difference increases by 65%near room temperature.This work greatly broadens the commercial application potential of ntype Bi_(2)Te_(2.5)Se_(0.5),and demonstrates magneto-trapped carrier effect as a universal strategy to enhance the electro-thermal conversion performance of TE materials with high carrier concentration.