粗粒土最大干密度试验研究

采用自行研制的大型击实仪，对粗粒土进行了击实试验。试验结果表明：粗颗粒含量对粗粒土的最大干密度影响较大，其中粗颗粒含量为70％是粗粒土最大干密度变化的分界点；最大粒径对粗粒土的最大干密度和最佳含水量影响较小。粗粒土的最佳含水量随粗颗粒含量增加而减小，且当粗颗粒含量大于70％时，粗粒土中细粒土的含水量急剧增加。     

橡胶-砂混合隔振材料初始变形模量试验研究

通过对橡胶-砂混合隔振材料开展不排水三轴试验，探究了橡胶含量XC、粒径比d_50,r/d_50,s、相对密实度D_r以及围压σ₃对混合料初始变形模量的影响。结果表明：橡胶-砂混合料初始变形模量随着XC的增加呈指数下降，d_50,r/d_50,s越小，橡胶颗粒对初始变形模量的衰减影响越明显；初始变形模量随D_r和σ₃的增大而增大，D_r越大初始变形模量的增长速度越缓。对初始变形模量按Janbu经验公式进行拟合发现，参数K随橡胶含量的增加而减小；参数n在橡胶含量较小时波动较小，超过30%后离散性增大。最终提出橡胶-砂混合隔振材料初始变形模量归一化预测公式。     

超声波辅助制备癸酸-棕榈酸@改性SiO2调温调湿复合材料超声波辅助制备癸酸-棕榈酸@改性SiO2调温调湿复合材料

以硅烷偶联剂改性SiO₂为壁材,癸酸（DA）-棕榈酸（PA）为芯材,利用超声波辅助溶胶-凝胶法制备DA-PA@改性SiO₂调温调湿复合材料,分析了硅烷偶联剂用量、超声波功率、超声波时间和超声波温度对DA-PA@改性SiO₂调温调湿复合材料粒径的影响,以及相关性能。结果表明,利用超声波辅助溶胶-凝胶法制备DA-PA@改性SiO₂调温调湿复合材料,可以显著降低粒径尺寸和减小粒径分布。当硅烷偶联剂用量为4.0 g、超声波功率为120 W、超声波时间为100 min和超声波温度为60℃时,DA-PA@改性SiO₂调温调湿复合材料的粒径较小且粒径分布较窄,即d₉₀=87.36 nm、d₅₀=63.34 nm、d₁₀=44.02 nm和d₉₀-d₁₀=43.34 nm,在相对湿度40.0%~65.0%范围内的平衡含湿量为0.1864~0.2379 g/g,相变温度为20.23~23.59℃,相变潜热为40.91~46.72 J/g,稳定性能良好。      

二维堤坝管涌的数值模拟研究

根据修正的SPV(Stavropoulou-Papanastasiou-Vardoulakis)管涌控制方程,采用Newton-Raphson求解法和传导矩阵调整法,对二维带自由面的均质土石坝坝体渗流侵蚀问题进行了有限元数值分析。数值分析表明:在具有渗流自由面的均质土石坝坝体中,溢出面和自由面附近区域的水力梯度较大,比其他区域更容易大于管涌临界水力梯度。管涌侵蚀区(孔隙率明显增大)和细颗粒最大浓度区首先出现在溢出面处,然后沿着渗流自由面附近区域向上游扩展,最终达到自由面附近的进水面,形成孔隙率明显增大的侵蚀贯通通道。管涌侵蚀增大堤坝的渗透系数,它对堤坝渗透速度的影响较大,但对孔压分布和自由面位置的影响较小。     

双层黏土中自升式平台桩靴极限承载力数值分析

海底层状地基极限承载力的预测是海上自升式钻井平台插桩作业设计的关键。目前,成层土地基极限承载能力的确定主要依靠经验公式,但其适用范围和限制条件并不明确。为了研究桩靴在硬软双层黏土地基中的极限承载力,将自升式平台的插桩过程视为桩靴在半无限弹塑性地基上逐渐贯入的准静态过程,将土体视为满足摩尔-库伦屈服准则的各向同性弹塑性体,桩土之间的接触定义为符合库伦摩擦定律的主从接触面接触,在ABAQUS平台上利用非线性有限元法对自升式钻井平台桩靴在硬软双层黏土地基中的极限承载力进行数值计算,分析上、下土层强度比和上层土相对厚度比对极限承载力的影响,并与现有经验公式的结果进行对比。结果表明,BrownMeyerhof公式和投影面积法只适用于硬软差别明显的双层土地基。当上层土相对厚度比H/B一定时,上、下层土强度比Sut/Sub越小,双层土地基的极限承载力越大。当H/B=1.0时,只有在Sut/Sub3.0的情况下才可用BrownMeyerhof公式计算其极限承载力,而投影面积法适用于4.0Sut/Sub6.0的情况。当上、下层土强度比一定时,上层土相对厚度比越大,下部软土层对双层地基极限承载力的影响越小。在Sut/Sub=3.0时,只有在H/B1.0的情况下,BrownMeyerhof公式和投影面积法计算的双层土地基的极限承载力才是合理的。上、下层土强度比越大,上层土相对厚度比越小,发生穿刺的可能性就越大。所得结论对于插桩作业的设计和施工具有一定的工程指导意义。     

公路工程路堤临界填土高度一种计算方法研究

路堤临界填土高度是公路工程中一个非常重要的问题,填筑高度小于临界填土高度时,地基的变形和稳定能得到控制。依据极坐标表示的弗拉曼公式和统一强度理论,考虑中间主应力σ₂对地基承载力的影响,推导出土的静止侧压力系数K₀≠1条件下地基的临塑与临界荷载公式,提出路堤临界填土高度一种计算方法。结合算例,对中间主剪应力系数b和土的静止侧压力系数K₀取不同值时,临界荷载与路堤临界填土高度计算结果进行了对比分析,结果表明:基于统一强度理论得到的计算方法能确切地反映地基承载力的实质,使地基土体强度得到充分的发挥。     

快压缩P1波在饱和冻土与弹性基岩分界面上的能量传输特性

基于弹性波在冻结饱和多孔介质与单相弹性介质中的传播理论,选取了饱和冻土中传播速度最大的快压缩P₁波入射在饱和冻土与弹性基岩分界面上的能量传输问题。根据分界面上的边界条件,推导出了快压缩P₁波从饱和冻土介质入射到弹性基岩分界面上透反射振幅比和能量率的解析表达式。研究了快压缩P₁波入射在饱和冻土与弹性基岩分界面上的能量与入射角度,入射频率,温度(含冰量),孔隙率,胶结参数以及接触参数的关系。研究结果表明：当入射角度为0°时仅存在压缩波,达到临界角后透射P波消失;各种波在达到临界角时出现不同程度的脉冲,其中反射P₁波最为显著;随着胶结参数,孔隙率,接触参数的增大,临界角越早出现;入射频率仅对反射P₂,P₃和S₂波的能量反射率影响较大;当温度和含冰量较低或较高时,均不利于反射S₂波的能量产生。     

土工格栅-粗粒土界面考虑尺寸效应直剪试验研究

为研究土工格栅-粗粒土界面动力剪切特性受土粒径与格栅尺寸比(粒孔比d50/La)的影响,开展4种粒孔比d50/La(0.04、0.08、0.12、0.20)的循环剪切室内模型试验.试验结果表明:不同粒孔比d50/La下筋土界面循环剪切滞回曲线呈近似倾斜菱形;筋-土界面剪应力峰值随d50/La的增大呈先增后减的变化趋势,...     

考虑附加抗力影响的单桩水平受力分析方法

单桩基础受水平荷载作用时,桩身截面转动引起的竖向摩阻力形成土对桩的附加抗力矩,同时桩端土对桩也有一定的附加抗力效应。为了研究桩身和桩端附加抗力对单桩水平承载特性的影响,该文基于API规范推荐的砂土摩阻力模型,结合桩身径向土压力引起的极限摩阻力增强效应,推导出砂土中桩身抗力矩的离散数值解和简化公式解;采用API规范推荐的黏性土摩阻力模型,推导出黏性土中桩身抗力矩的离散数值解和简化公式解。基于双曲线桩端竖向应力-位移模型,在考虑桩端桩-土界面脱开效应的基础上,得到了桩端抗力矩的离散数值解和简化公式解,桩端水平剪力的离散数值解;进而提出基于Winkler地基梁模型的有限元计算方法,并编制了程序。通过对比试验数据,初步验证了该文方法的正确性,进行了水平承载力的参数分析,结果表明:随着长径比的增加,附加抗力在总水平承载力中的占比逐渐减小;而随着桩直径的增加,附加抗力在总水平承载力中的占比并未显著变化。     

弹性模量比对界面迁移下夹杂演化的影响

集成电路的导线内不可避免存在夹杂等缺陷。在各种内在机制以及外界环境作用下夹杂会出现形态演化从而影响内连导线的各种性能。该文基于界面迁移机制下微结构演化理论,推导了应力诱发固-固界面迁移的单元控制方程,数值模拟了夹杂-基体弹性模量比对夹杂形态演化的影响。结果表明:不同模量比下夹杂的σ>σ_c、β>β_c或hc时,夹杂长大;反之收缩。随着模量比的增加,临界应力、临界形态比随之增大,而临界线宽会减小。并且,当夹杂与基体的弹性模量比α>0.6时,模量比对于临界应力和临界形态比的影响可忽略。     

Conveying of Solid Particles in Newtonian and Non-Newtonian Carriers

This article deals with the effect of slurry composition and volumetric concentration on the flow behavior of slurries containing fine-grained and coarse-grained particles. Fluidic fly and bottom ash slurries and sand slurries were experimentally investigated. Kaolin slurries with and without a peptizing agent were used as the carrier liquid for the sand slurries to compare the effect of Newtonian and non-Newtonian carriers. The study revealed a time-dependent yield pseudo-plastic behavior of fluidic fly and fly/bottom ash slurries and the possibility of substantial reduction of the flow resistance by mechanical treatment or by the arrangement of particle size distribution. The flow behavior of fluidic ash slurries can be approximated by the Bulkley-Herschel model in the laminar region. In the turbulent region, the Wilson or Slatter models can be used. The effect of the size distribution of the sand slurry on the hydraulic gradient depends on the flow velocity. The coarse sand slurry reaches a higher hydraulic gradient than the fine sand slurry: the difference decreases with growing velocity. The highly concentrated sand-kaolin slurries show non-Newtonian behavior. When the carrier kaolin slurry is peptized, the hydraulic gradient in the laminar region becomes markedly lower, and the favorable effect vanishes in the transitional and turbulent regions. The addition of small amounts of kaolin favorably affects the flow behavior of the sand slurry.     

Unusual grain-size and strain-rate effects on the serrated flow in FeMnC twin-induced plasticity steels

The purpose of the paper is to clarify the serrated flow behavior and to explore the grain-size and strain-rate effects on serrations in coarse- and fine-grained FeMnC twin-induced plasticity (TWIP) steels at room temperature. Tensile tests were performed under extensometer-measured strain control, rather than under conventional cross-head displacement control, at strain rates ranging from 6 × 10^?6 to 6 × 10^?3 s^?1. The results indicate that both the coarse- and fine-grained steels show different types of serrations, which depend on strain rate, and demonstrate a nonmonotonic strain-rate sensitivity of the critical strain for the onset of serrations, i.e., a positive strain-rate sensitivity of the critical strain in the high strain-rate region typified by type A serrations, and a negative strain-rate sensitivity in the low strain-rate region typified by type C ones. As compared to the coarse-grained steel, the fine-grained steel increases the critical strains, showing an inverse grain-size effect. The findings suggest that the fine-grained FeMnC TWIP steel suppresses the serrated flow, possibly due to the enhanced dynamic recovery associated with the decreased planar slip length in the fine-grained low stacking-fault-energy steel.     

Effect of microstructure on the erosion and impact damage of sintered silicon nitride

The erosion rates and impact damage of two sintered silicon nitride materials with identical compositions but different microstructures were determined as a function of impacting particle (SiC) kinetic energy and temperature (25–1000° C) using a slinger-type erosion apparatus. The coarse-grained silicon nitride had significantly better resistance to impact damage than the fine-grained material. Crack-microstructure interactions were characterized using scanning electron microscopy and showed that crack-bridging was an important toughening mechanism in the coarse-grained material. Post-impact strength data were significantly less than those predicted from the indentation-strength data, due to impact flaws linking up prior to fracture. Consistent with its greater fracture resistance, the erosion rate of the coarse-grained material was less than that of the fine-grained material for erosion at 25 deg, and was independent of erosion temperature.     

Discrete element modeling of granular hopper flow of irregular-shaped deformable particles

Many natural and engineered granular materials have relatively deformable particles. Besides particle size and shape, particle deformability is another salient factor that significantly impacts the material’s flow behavior. In this work, the flow of irregular-shaped deformable particles in a wedge-shaped hopper is investigated using discrete element simulations. A bonded-sphere model is developed to simultaneously capture irregular particle shapes and particle-wise deformations (e.g., compression, deflection, and distortion). Quantitative analysis of the effects of irregular shapes and particle deformations shows that the increase in particle stiffness tends to increase initial packing porosity and decrease the flow rate in the hopper. Rigid particles tend to have clogging issues, whereas deformable particles have less chance to, indicating particle deformation reduces the critical bridging width in the hopper flow. Detailed analysis of stress fields is also conducted to provide insights into the mechanism of particle flow and clogging. Stresses and discharge rates calculated from numerical simulations are compared and show good agreement with Walker’s theory and the extended Beverloo formula. Simulations with various particle shape combinations are also performed and show that the initial packing porosity decreases with an increasing percentage of fibers while the discharge rate has a complex dependency on particle shapes.     

Effect of Particle Size on Deformation and Compaction Characteristics of Ascorbic acid and Potassium Chloride: Neat and Granulated Drug

Deformation and compaction characteristics of two soluble drugs, ascorbic acid and potassium chloride, were investigated. Five different particle size fractions of ascorbic acid with mean particle size (d₅₀) ranging from 30-300μm and four different particle size fractions of potassium chloride with d₅₀ ranging from 20-400 μm were selected in the study. The compaction behavior of the drug substances as neat drugs or as granulated drugs were evaluated on both a Carver press and an instrumented single-punch tablet press. The results clearly show that mean particle size of the drug substances plays an important role in their compactibility. Intrinsic compactibility of both drug substances was slightly improved with increased particle size. Granulations of the drugs with polyvinyl pyrrolidone significantly improved their compactibility. However, this effect was more pronounced in the drug substance with finer particle size. The Heckel plots indicate that deformation characteristics of both granulated drugs were related to their original mean particle sizes. The granulations prepared from the coarser particle size (d₅₀ 250 μm to 400 μm) underwent two stages of deformation, so-called “brittle fracture” and “plastic deformation”. While the granulations prepared from the finer particle size predoninantly underwent “plastic deformation”. The results indicated that the plastic deformation of both granulated drugs was progressively enhanced whilst fragmentation of particles was correspondingly reduced as the particle size of the drugs was decreased. Scanning electron photomicrographs indicated that the granulation process changed the surface morphology of the drug particles imparting more “microirregularities” or “defects”, thereby providing greater “interparticulate bonding” as compared with the neat drugs. Optimum particle size range of ascorbic acid and potassium chloride for satisfactory compactibility was found to be 30-40 μm and 20-40 μm, respectively. The present study demonstrates the importance of selecting the appropriate particle size of drug for the development of tablet dosage forms.     

SOIL STRUCTURE CHARACTERIZATION USING ELECTROMAGNETIC WAVES

The interaction effects of particle shape, orientation, porosity, and relative disparity between electrical parameters (conductivity and dielectric constant) of soil particles and pore fluid on electrical response of bulk soil at very low and very high frequencies of excitation by an alternating current are studied and compared with experimental data. The type of pore fluid and soil mineral can have a large influence on the response. The ratio of conductivities (and permittivities) of the solid particle to pore fluid has a significant influence on the electrical response of soils. Higher ratios reduce the effects of particle shape and the anisotropy arising from particle orientation. Results indicate that the electrical response, in general, can be used to characterize soil structure, detect anisotropy and identify pore fluid characteristics.     

不同TiB2颗粒粒径的TiB2/Cu复合材料耐电弧侵蚀行为

采用放电等离子烧结法（SPS）制备了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料,研究了3wt% TiB₂/Cu复合材料致密度、导电率、硬度和耐电弧侵蚀性能随TiB₂颗粒粒径的变化规律,重点分析了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料耐电弧侵蚀行为。结果表明:3wt% TiB₂/Cu复合材料致密度和硬度随TiB₂颗粒粒径的增大而略有降低;TiB₂颗粒粒径越小,TiB₂/Cu复合材料的综合性能越好。随着TiB₂颗粒粒径的增大,3wt% TiB₂/Cu复合材料耐蚀稳定性降低,3wt% TiB₂/Cu阴极材料的损耗量明显增加;当TiB₂颗粒粒径为10 μm时,3wt% TiB₂/Cu复合材料的耐电弧侵蚀性能最佳。电弧蚀形貌观察表明:不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料经电弧侵蚀后,3wt% TiB₂/Cu复合材料均由阴极向阳极发生转移;随着TiB₂颗粒粒径的增大,阴极质量损耗逐渐增加,触头表面电弧侵蚀面积增加;而在Cu基体中引入较小的TiB₂颗粒,有利于减弱电接触实验过程中TiB₂/Cu复合材料的喷溅现象。      

Predicting porosity of binary mixtures made out of irregular nonspherical particles: Application to natural sediments

Predicting porosity or packing density of sediments made of coarse and fine components of arbitrary geometry is critical to many science and engineering applications. Well-established analytical models for packing of spheres express porosity of the binary mixture as a function of fine-to-coarse particle size ratio. Nevertheless, the applicability of such models to natural granular materials is limited given the nonspherical and irregular nature of the particles whose packing depends on both particle size and shape. The objective of this study is to develop a model that predicts the porosity of binary mixtures made up of irregular nonspherical particles. We modified a previously developed linear sphere-packing model so that it takes into account the effect of both the particle size and shape. As an input, the modified model uses the coarse-to-fine particles specific surface area ratio instead of using the particle size ratio required by the sphere-packing model. We tested the modified model by predicting the porosities of a binary mixture composed of coarse and fine calcite aggregates. We further validate the model by using published data on the porosity of binary mixtures made of synthesized, cubical and cylindrical particles. Our model predictions show good agreement with the measured porosity.     

Multi-scale study of particle flow in silos

The flow characteristics of solid particles in a silo were studied experimentally and theoretically. A multi-scale study of the particles flow was performed by means of discrete element method (DEM). The dependence of flow behaviors on the particles diameter distribution and silo geometry was analyzed to establish the spatial and statistical distributions of microdynamic variables related to flow and silo structures such as velocity, porosity, coordination number, and interaction forces between particles. The results show that the distribution of particle diameter has great effects on particles flow, and the mixing of multi-sized particles is propitious to granular flow. The geometry of silos has greater effects on granular flow than particle size distribution, and inserts can improve the flow behaviors of “funnel flow” type to “mass flow”. Linear equations can be used to describe the relationship between discharge rate and orifice size by G^2/5 vs. D_o for the same distribution of particles diameter. The flow structure of particles in the silos is spatially non-uniform, which is illustrated by spatial and statistical distributions of porosity and coordination number. Both porosity and coordination number are affected by the mode of particles packed, which is affected by the geometry of silos and particle size distribution. The distribution of contact forces between particles is spatially non-uniform too. In flat-bottomed silo, there are arched stress chains in the vicinity of the orifice under the “bridging action”, which disappeared in wedge-shaped hopper silo.