Preparation of Layered Potassium Titanate Whiskers with Large Length-diameter Ratio by KDC Method

Pure K2Ti4O9 whiskers were prepared by KDC（Kneading-Drying-Calcination） method with TiO2 and K2CO3 as raw materials. The influences of TiO2/K2CO3 molar ratio（RT/K）, calcination temperature（TC） and cooling process on phase composition and morphology of the whiskers were investigated by TG-DSC（thermo gravimetric-differential scanning calorimeter）, XRD（X-ray diffraction）, and SEM（scanning electron microscope）. Pure K2Ti4O9 potassium titanate whiskers with large length-diameter ratio（r）（over 250） can be obtained at RT/K = 2.9 and TC = 950 ℃.

On the Elastic Vibration Model for High Length-Diameter Ratio Rocket with Attitude Control System

An elastic vibration model for high length diameter ratio spinning rocket with attitude control system which can be used for trajectory simulation is established. The basic theory of elastic dynamics and vibration dynamics were both used to set up the elastic vibration model of rocket body. In order to study the problem more conveniently, the rocket's body was simplified to be an even beam with two free ends. The model was validated by simulation results and the test data.

The Growth of Latex Particles during the VAc/BA Copolymerization

The semi-continuous seeded emulsion eopolymerization of vinyl acetate and butyl acrylate was carried out with hydroxyethyl cellulose as a colloid stabilizer. The morphology of the latex particle and the relationship between the reaction time and the average particle diameter and/or the conversion ratio during the polymerization were invstiguted. The experimental results shaw that the morphology of the latex particle possesses the stable sterie construction. In the seeded polymerizution, the average particle diameter of latex decreased while the conversion ratio increased. At the second term of the emulsion copolymerization （the growth stage of particle size）, the latex particle average diameter increased with copolymerization continuously, but the instantaneous conversation ratio was not large, so it was very necessaO to properly prolong the time during the holding temperature stage.

Behaviour of Batter Micropiles Subjected to Vertical and Lateral Loading Conditions

Micropiles are drilled and grouted piles having diameter between 100 to 250 mm. Due to its small diameter, it is suitable for low headroom and limited work area conditions. It can be installed without noise nuisance, without vibrations to surrounding soils and structures and without disruption to the production operations in industries which makes micropiles suitable for underpinning and seismic retrofitting of structures. It is necessary to therefore understand the behaviour of micropiles under different loading conditions. This work is on vertical and battered micropiles with different length/diameter ratio (L/D) subjected to vertical and lateral loading conditions. Batter angles had a significant influence on both the vertical and lateral load carrying capacity. The ultimate vertical load was found to increase upto a 30°batter. The ultimate lateral load was found to increase significantly with increasing L/D ratios upto an L/D ratio of 30 for vertical and 48 for battered piles, beyond which the increase was found to be not significant. In general, negative battered micropiles offered more lateral resistance than positive battered micropiles. The results of the study indicated that the ultimate load capacity and mode of failure of the micropiles are a function of the angle of batter, direction of batter and the L/D ratio for vertically and laterally loaded micropiles.

Optimization Analysis of the Mixing Chamber and Diffuser of Ejector Based on Fano Flow Model

An improved model to calculate the length of the mixing chamber of the ejector was proposed on the basis of the Fano flow model,and a method to optimize the structures of the mixing chamber and diffuser of the ejector was put forward.The accuracy of the model was verified by comparing the theoretical results calculated using the model to experimental data reported in literature.Variations in the length of the mixing chamber L_(m) and length of the diffuser L_(d) with respect to variations in the outlet temperature of the ejector T_(c),outlet pressure of the ejector p_(c),and the expansion ratio of the pressure of the primary flow to that of the secondary flow p_(g)/p_(e) were investigated.Moreover,variations in L_(m) and L_(d) with respect to variations in the ratio of the diameter of the throat of the motive nozzle to the diameter of the mixing chamber d_(g0)/d_(c3) and ratio of the outlet diameter of the diffuser to the diameter of themixing chamber d_(c)/d_(c3) were investigated.The distribution of flow fields in the ejector was simulated.Increasing L_(m) and d_(c3) reduced T_(c) and p_(c).Moreover,reducing p_(g)/p_(e) or d_(g0)/d_(c3) reduced T_(c) and p_(c).The length of the mixed section L_(m2),which was determined on the basis of the Fano flow model,increased as pg increased and decreased as d_(c3) increased.The mixing length L_(m1),which was considered the primary flow expansion,showed the opposite trend with that of L_(m2).Moreover,Ld increased as p_(g)/p_(e) and d_(c)/d_(c3) increased.When the value of d_(c) was 1.8 to 2.0 times as high as that of dc3,the semi-cone angle of the diffuser ranged between 6°and 12°.At a constant dc/dc3,decreasing T_(c) and pc increased Ld.

A Parametric Approach to the Evaluation of Flexural Strength of Advanced Ceramic or Glass Like Cylindrical Rods at Ambient Temperature

This critical review presents a parametric approach to the evaluation of flexural strength of advanced ceramic or glass like cylindrical rods at ambient temperature.The parameters governing the measurement and evaluation of flexure strengths of glasses and ceramics are detailed with references.The scope for improvement in the existing ASTM STM C-1684 standard is described with a logical rationale and the parameters that need to be addressed are listed and explained.

Quantifying.Associations among Dimensions of Ears and Their Form Factors in Maize(Zea Mays)Using Dimensional Analysis

Ear morphological traits such as volume and shape are important features of maize and the quantitative associations among them can help understand kernel yield determination. 150 mature ears each of 4 maize cultivars were collected from field experiments, and ear length(L), diameter(D), area(S) and volume(V) were recorded for individual ears, kernel weight per ear also recorded for a portion of the examined ears. Following principles of dimensional analysis, 8 theoretical equations of 3 sets,which relate ear higher dimensions to its length and diameter, were developed and parameterized and validated with the field observations. The 3 optimized equations showed that the shape of ears in maize can be featured with 3 dimensionless form factors, namely diameter-to-length ratio(c=D/L), areal form factor(b=S/L/D), and volumetric form factor(a=V/L/D/D). Statistically,all of them were significantly different among cultivars, and a's values varied from 0.582 to 0.612, and b's 0.839-0.868, and c's 0.242-0.308. Volumetric form factor and areal form factor could estimate precisely ear volume and area respectively, but diameter-to-length ratio was not suitable to estimate ear diameter by its length. Ear volume explained almost all variation of ear kernel weight and product L*D*D did the same substantially. Dimensional analysis proved to be promising in understanding relationship among morphological traits of ears in maize. Its application in crop researches should improve our knowledge of the physical properties of crop plants.

不同冲击气压下煤样动态剪切强度的长径比效应

采用Φ50mm分离式霍普金森压杆(SHPB)试验系统,开展了不同冲击气压下直径75mm,长径比分别为0.20,0.27,0.33,0.40和0.47的5组煤样的动态剪切试验,划分了煤动态剪应力时程曲线的阶段,探讨了冲击气压对煤样动态剪切强度的影响,分析了煤样动态剪切强度和加载率的长径比效应,并建立了长径比效应理论模型。研究结果表明:①煤样动态剪应力时程曲线可分为应力初始上升、应力线性增长、应力缓慢上升和应力下降4个阶段;②煤样动态剪切强度与冲击气压呈正线性相关,但不同长径比下增加幅度存在差异,具体表现为:相同冲击气压增量下,煤样长径比越小,动态剪切强度的增加幅度越大;③煤样动态剪切强度和加载率均与长径比有关,在0.25,0.35 MPa较低冲击气压与0.45,0.55 MPa较高冲击气压下分别呈现出正、负长径比效应,并通过方差分析确定了长径比对其影响最小的冲击气压为0.376MPa;④建立了不同冲击气压下煤样动态剪切强度长径比效应理论模型,通过加载率效应推导出加载率长径比效应理论模型,并验证了模型的合理性和准确性。

深海无人系统大长径比环肋圆柱壳结构设计与试验研究

环肋圆柱壳是深海无人系统广泛采用的一种耐压结构形式,保障其结构安全是系统研制过程中非常重要的一环。针对环肋圆柱壳的结构特征推导了组合结构重量关系式和结构参数简化估算方法,并以一种超长型深海无人系统耐压结构为例,围绕大长径比环肋圆柱壳的结构形式、设计计算、仿真分析、模型验证等开展研究。研究表明提出的大长径比环肋圆柱壳结构设计参数简化估算方法具有较好的适应性。相关计算和分析结果可以为该型深海无人系统结构设计提供技术支撑,也可以为其他类似耐压结构设计提供参考。

重力参数对非阻塞性颗粒阻尼减振特性的影响

针对非阻塞性颗粒阻尼(Non-obstructive Particle Damping,NOPD)在微重力、超重及离心等非常态环境中减振效果较差的问题,采用重力加速度表征这些非常态物理环境,利用离散元法(Discrete Element Method,DEM)研究重力参数对NOPD减振特性的影响,同时还分析NOPD最优填充比及最优粒径比等结构参数在不同重力条件下的变化规律。研究表明,重力加速度在0.7~1.0 g之间时NOPD减振效果最好。在微重力环境下,当重力参数变化时,NOPD最优填充比为0.85,最优粒径比为0.45。而当重力加速度大于1 g时,NOPD最优填充比及最优粒径比均随重力加速度的增加而减小,且其最优范围也均有所扩大。

对辊制粒机压辊的有限元分析及优化

对辊制粒机的压辊在工作过程中由于受交变载荷作用寿命往往较短,为改善压辊受力状况,根据对对辊制粒机制粒成型过程的分析以及对压辊受力状况的研究,建立了压辊的力学模型;在此基础上,以某型对辊制粒机为初始模型,通过有限元软件Abaqus探究了压辊表面应力分布情况,并进一步对其长径比及支撑方式进行了优化,结果表明:压辊长径比为1.034时,最大应力比初始模型减小了8.92%,单侧支撑改为双侧支撑可使最大应力减小65.31%,因此这两种优化方式对提高压辊的使用寿命具有重要参考价值。

抗拔桩承载能力影响因素与群桩变形规律试验研究

利用自主研发的桩基室内抗拔测试装置,结合数值模拟技术对抗拔桩的承载破坏过程及影响因素、群桩的协同工作特征展开了深入研究。结果表明:抗拔桩的承载破坏经历4个阶段,承载初期,桩顶侧摩阻力最先发挥作用,桩顶土体发生塑性破坏;随上拔荷载不断增大,桩体产生相对位移,桩周土体由于桩身侧摩阻力产生塑性破坏;当桩身轴力自桩顶传递至桩底时,桩身底端产生抗拔“吸附力”,并伴随局部土体塑性破坏;随着桩周土体塑性区的拓展、连通,抗拔桩承载能力达到极限;桩身长径比、桩-土界面摩擦因数、桩侧土体压力与其承载极限呈正相关关系,其中桩身长径比对桩端“吸附力”具有重要影响;群桩抗拔过程中,角桩侧摩阻力发挥最充分,桩身位移量最小,极限承载力最大,中心桩桩身位移最大,极限承载力最低;距径比影响抗拔桩的群桩效应,当距径比从2增大至8时,桩身侧摩阻力提高30%,将距径比8作为群桩工程的推荐值,6~10作为群桩距径比的推荐范围。

基于CFD流场模拟的大型卧式反应釜结构研究

近年来,加压浸出湿法冶金工程在向更大规模的发展道路受到了配套装备大型化带来的技术制约。为了适应加压浸出工艺关键核心设备-卧式反应釜的规模大型化发展,更好地保证该设备在使用过程中的可靠性与高效性。本文采用CFD流体模拟软件,针对某项目使用的300立卧式反应釜,研究其在不同长径比下的流场分布情况以及搅拌器功率消耗大小与长径比的关系。研究表明适当增加长径比有利于改善水平方向的流场特性,减小长径比有利于改善垂直方向的流场特性,减小长径比有利于搅拌功率的降低。当长径比取1.08或1.13,能够有效提高卧式反应釜内的反应效率,降低成本和系统能耗。

超临界二氧化碳破口喷放特性数值分析

超临界二氧化碳布雷顿循环系统在发生小破口事故时破口位置处因系统内外压差出现的复杂喷放现象尚未研究清楚。为探究不同上游滞止参数与管道长径比对喷放特性的影响,本文采用数值模拟方法开展三维压力容器小破口喷放现象研究。研究结果表明:上游滞止压力升高或滞止温度降低引起质量流量增加,长径比增加时质量流量减少。上游滞止参数对流量的影响机理主要是参数变化引起密度发生较大改变从而影响喷放质量流量,管道长径比对流量的影响主要因为直径的变化。滞止压力升高时3组工况流量增加值相差5.3%,滞止温度降低时3组工况流量增加值相差90.7%,相比于压力对喷放流量的影响,温度对流量增加速率影响更为显著。

基于两端起爆的近地冲击波超压增益机制研究

两端起爆能够改变装药爆炸能量输出结构,增强装药爆炸近地冲击波超压威力。探明两端起爆对近地冲击波超压的增益机制,对提升装药能量利用效率具有指导作用。研究建立了大场域冲击波威力仿真模型,计算分析装药内部爆轰波叠加前后压力变化,研究两端起爆的近地冲击波威力场特征。在多种长径比工况下,观测冲击波威力场特征演化,解析装药两端起爆对近地超压威力场的增益机制。开展20 kg级不同长径比静爆试验,验证两端起爆对近地超压的增益机制。研究发现:两端起爆装药内两爆轰波相撞,形成了两道轴向反射波和一道径向强冲击波,冲击波威力场在二者影响下形成了双反射波系结构,相较一端起爆,双反射波系对近地冲击波超压有显著增益。仿真计算与试验结果表明,装药长径比3.5时,两端起爆对近地冲击波超压增益达到最优。

涡环输送特性的实验与仿真分析

为探究结构变化对涡环输送的作用,设计一种基于空气驱动活塞运动模式的空气涡环发生器,采用实验方法研究了涡环发生器的长径比、环径比及活塞停顿时间对涡环输送特性的影响,通过数值仿真对涡环输送过程的速度场和压力场进行分析。结果表明:长径比与环径比对涡环输送特性影响较大,活塞停顿时间的影响较小,其中涡环输送的最远距离为277 cm;长径比过大会造成较大沿程损失,环径比过大会造成较大局部损失,阻碍涡环的生成和输送,而涡环具有在较小能量耗散的同时远距离输送的特性。

振动辅助Ti-45Nb钛合金冷镦成形有限元模拟研究

在金属塑性成形加工中,振动辅助成形技术的应用可以有效地降低零件成形载荷,提高产品质量。本文首次基于塑性大变形理论和有限元数值模拟,对Ti-45Nb钛合金振动辅助冷镦成形机理进行了分析与研究。首先以位错密度的变化作为内变量描述材料在变形过程中材料软化、硬化等关系,建立了振动辅助冷镦成形本构模型,并采用MATLAB工具编程拟合出本构方程中的材料参数。然后利用Deform有限元软件对Ti-45Nb钛合金的大长径比薄壁零件进行建模仿真分析,根据反挤压道次中材料成形流动情况的结果,对模具中应力集中的凸模结构进行优化设计。结果表明:本文基于大变形建立的本构模型能够有效描述振动的软化作用,尤其在材料塑性变形阶段拟合较好,预测精度评估相对系数(RC)值>0.994。此外,通过建模仿真分析得出的多级倒角结构可有效促进材料流动,减小模具磨损,提高模具寿命。

不同长径比柱形炸药水下爆炸气泡动力学行为特性

采用实验与数值模拟相结合的方法,研究了不同长径比的柱形装药在固支方板下爆炸气泡动力学行为;对质量2.5g、长径比分别为1∶1和2∶1的TNT炸药进行了水中固支方板下的爆炸实验,利用高速摄影记录爆炸气泡演化图像;使用ABAQUS软件对长径比为5∶1、10∶1、20∶1的柱形装药,在竖直与水平设置条件下的水下爆炸气泡演化过程进行了数值模拟。结果表明,炸药长径比为1∶1和2∶1时,爆炸气泡演化现象无明显差别。当药柱竖直放置时,由于炸药长径比不同导致的爆炸气泡初始形态差异,会在气泡演化过程中迅速消弭;但长径比与起爆位置都对射流速度有不同程度的影响;当药柱水平放置时,起爆点位置会影响气泡的对称性和水射流形态;药柱端部起爆时,气泡膨胀过程的形态略微不对称,水射流向起爆点方向偏移;炸药长径比越大爆炸水射流在气泡内部越宽,并且水射流的载荷越小;药柱中心起爆时,爆炸气泡产生竖直向上的水射流,不发生偏移。

单掺和双掺不同长径比钢纤维对全轻混凝土力学性能的影响

为研究单掺和双掺不同长径比钢纤维对免烧结粉煤灰陶粒全轻混凝土力学性能影响,选用体积掺量为1%的剪切钢纤维作为增强材料,以钢纤维长径比(18.75,25和31.25)和掺入方式(单掺、双掺)为试验参数,对LC30全轻混凝土进行立方体抗压强度、轴心抗压强度、抗折强度、劈裂抗拉强度和弹性模量试验。试验结果表明:钢纤维能明显改善全轻混凝土的力学性能;不同的长径比和掺入方式对全轻混凝土的抗折度和劈裂抗拉强度影响较大,对立方体抗压强度和轴心抗压强度影响较小,对弹性模量几乎没有影响。

爆炸动载下金属柱壳破片速度场分布研究

针对格尼(Gurney)公式无法描述破片速度场沿圆柱壳体轴向变化的问题,该文通过AUTODYN软件建立仿真模型,分析了长径比和壳体壁厚对破片速度场分布的影响。考虑爆炸加载下壳体断裂过程,修正了Gurney公式。基于上述研究,将壳体长径比和相对壁厚引入指数形式的修正因子中,建立了破片速度场轴向分布模型。通过实验验证了该模型的合理性。研究结果表明:对于圆柱形战斗部,相对壁厚为常数,长径比越大,战斗部形成破片速度越接近v 0;长径比为常数,壳体相对壁厚越小,战斗部形成破片速度越接近v 0。将该文理论结果与Gurney理论结果以及实验结果进行对比,该文理论结果误差均在7%以内,大部分误差小于3%,与实验结果更加吻合,验证了该文建立的破片速度场轴向分布模型的合理性。该文理论模型可为杀伤战斗部破片参数精准设计提供参考。