爆炸荷载下钢管混凝土墩柱的动力响应研究

设计并制作了3根普通钢管混凝土墩柱和1根复式中空钢管混凝土墩柱,进行了TNT药量分别为3 kg和50 kg的3发4工况静爆试验,获得构件的迎爆面及背爆面的柱面超压分布、残余变形以及最终破坏形态,结合有限元分析,研究了爆炸荷载下钢管混凝土墩柱的动态响应、破坏模态及参数影响。研究表明:50 kg TNT作用下、比例距离为0.14 m/kg1/3时,外径同为273 mm、壁厚为7 mm的普通钢管混凝土墩柱抵抗爆炸荷载的变形能力优于中空钢管内径为50 mm、壁厚为4 mm的复式钢管混凝土墩柱;基于试验结果建立了多物质流固耦合的数值模拟方法,可有效模拟钢管混凝土墩柱在爆炸荷载下的动态响应;钢管混凝土墩柱三种典型破坏形态分别是:低超压峰值-高持时发生弯曲破坏、高超压峰值-低持时发生剪切破坏及介于两种情况之间的弯剪破坏;炸药当量为50 kg,比例距离z>0.3 m/kg1/3时,爆炸荷载下试件柱的残余变形可忽略不计;核心混凝土强度等级的增强以及含钢率的提高,可有效降低柱中点水平残余变形;提高钢管屈服强度,可降低柱中残余变形,当钢材强度等级≥345 MPa时,继续增大屈服强度对提高钢管混凝土墩柱的抗爆性能意义不大。     

爆炸荷载下装配式桥墩损伤因素灰色关联分析

装配式桥墩在桥梁施工领域得到广泛的应用，常受偶然爆炸或恐怖袭击的打击影响。为研究爆炸荷载下装配式桥墩损伤因素的影响规律，采用ANSYS/Workbench建立了近场爆炸荷载作用下的装配式桥墩数值模型，基于桥墩剩余承载力，提出以破坏参数D作为抗爆性指标，以炸药当量、爆心距离、初始预应力大小、节段数和剪力键的设置为损伤因素，分析了5种因素对桥墩损伤程度影响。在此基础上，利用灰色关联分析法衡量爆炸荷载下装配式桥墩损伤因素之间关联度的指标与贡献度。结果表明：增大初始预应力、节段间设置剪力键其破坏参数D的综合降低率为32.1%、29.6%,均能有效降低墩柱的损伤，与装配式桥墩抗爆受损有良好的关联性；而增加剪力键高度和节段数为12%、7.2%,对墩柱损伤影响较小；5种因素对爆炸荷载下装配式桥墩损伤影响的关联度从大到小为：TNT当量、爆心距离、初张拉预应力、剪力键的设置、节段数量。装配式桥墩抗爆设计中，可优先考虑提高初张拉预应力大小、设置剪力键等关联度较大的因素，灰色关联分析法对爆炸荷载下装配式桥墩损伤因素分析具有一定的参考性。     

大跨连续刚构桥双肢薄壁墩抗震性能研究

为获得双肢薄壁墩在地震作用下的破坏形态与力学性能,采用低周反复荷载试验探讨了不同轴压比、主筋率及体积配箍率对该类型桥墩抗震性能的影响,得到了各试验墩的破坏特性、滞回曲线、位移延性与耗能性能。试验结果表明:各试验墩的破坏形态基本相似,大体可分为三个阶段:弹性阶段、弹塑性阶段、弯曲破坏阶段。试验墩在墩底及系梁处破坏严重,其中墩底与墩顶出现显著的弯曲破坏,系梁处出现“X形”裂缝。主筋率较高的双肢薄壁墩滞回曲线较为饱满,耗能性能良好,适当提高轴压比可显著提高该桥墩的延性性能。各试验墩的变形能力较好,位移延性在2.63~3.68,变化幅度较大,主筋率对延性影响显著。     

爆炸荷载下钢管混凝土构件动态响应的数值模拟与试验验证

通过数值模拟和试验两种方法对爆炸荷载下钢管混凝土构件(CFST)的动态响应进行研究.首先基于LS-DYNA非线性有限元分析软件,采用多物质流固耦合方法,建立爆炸荷载下CFST数值模型;其次,设计三根钢管混凝土试件的爆炸罐内近距爆炸试验,并基于试验结果对数值模型的有效性及合理性进行了验证;最后总结爆炸荷载作用下CFST的破坏规律,并通过参数化分析方法,研究核心混凝土强度与钢管厚度对CFST抗爆性能的影响.结果表明:数值模拟方法能够有效合理地反应CFST在爆炸荷载作用下的动态响应,对比爆坑深度和测点加速度的模拟结果与试验结果,误差均在10％以内;近距离爆炸荷载下,CFST结构的破坏形式可分为4个阶段:迎爆面破坏、跨中弯曲变形、端部受拉、振动阶段;提高核心混凝土强度和增大钢管厚度都能改善CFST的抗爆性能,核心混凝土等级为C50、C70、C80的构件背爆面中心位置位移最大值相比于C30等级分别减小了2.3％、4.3％、5.3％,钢管厚度为4 mm、5 mm、6 mm的构件相比于3 mm钢管背爆面中心位置位移最大值分别减小了17.0％、28.6％、37.4％,钢管厚度对结构抗爆性能的改善效果更为明显.     

配筋对超高性能混凝土抗爆性能的影响

爆炸荷载作用下，超高性能混凝土(UHPC)防护结构的内部配筋形式对抗爆性能具有显著影响。该文利用数值方法研究不同配筋形式对超高性能钢筋混凝土抗爆性能的影响。使用试验结果验证数值建模方法和材料参数的可靠性，建立32个不同钢筋直径和间距的炸药-空气-UHPC-钢筋数值模型，通过分析结构的局部破坏和背爆面位移，给出近爆作用下不同配筋形式的超高性能钢筋混凝土结构抗爆特性。研究表明：不同配筋率下，钢筋-UHPC结构的动态损伤规律具有相似性；配筋率相同时，钢筋直径是影响结构抗爆性能的主要因素。局部加载时，采用细钢筋的UHPC结构抗爆性能优于粗钢筋，其中均匀布筋效果最优。而整体加载时，不同配筋方式的UHPC结构损伤差异较小。     

爆炸荷载下桥墩挂板防护性能研究

为研究挂板对桥墩在爆炸荷载作用下的防护性能,利用ANSYS/LS-DYNA建立钢筋混凝土板爆炸数值模型并验证其有效性,对有无挂板防护空心截面桥墩数值模型在爆炸下的响应与破坏进行分析比较,通过观察应力波的传播过程、桥墩的破坏形态以及背爆面位移,进一步讨论挂板面板厚度、芯层密度及芯层厚度等关键参数对挂板爆炸防护效果的影响....     

结构内爆炸荷载作用下钢筋钢纤维混凝土抗爆墙设计探讨

基于内爆炸原理,分析了结构内爆炸荷载的组成,提出了内爆炸荷载作用下抗爆墙的解析计算方法,对钢筋混凝土抗爆墙设计进行优化;提出将钢纤维应用于抗爆墙设计,并结合实例对钢筋混凝土与钢筋钢纤维混凝土抗爆墙进行计算对比。结果表明:准静态气体压力使结构内抗爆隔墙所受荷载比建筑外抗爆墙高出25%以上;在相同距离、相同爆炸当量条件下,钢筋钢纤维混凝土比普通钢筋混凝土抗爆墙厚度减少11%。     

复式空心钢管混凝土柱抗爆性能及损伤研究

通过爆炸试验,对复式空心钢管混凝土柱抗爆性能及损伤程度进行研究,并结合所得试验数据进行数值模拟,分析并建立柱的损伤评估准则。结果表明:在折合距离为0.14m/kg~(1/3)试验条件的爆炸荷载作用下,复式空心钢管混凝土柱迎爆面柱中发生了明显的塑性弯曲变形;柱迎爆面压力峰值柱中最高、柱底次之、柱顶最小,且爆炸冲击波对迎爆面柱中造成的破坏最为强烈、柱底次之、柱顶最小;柱端部节点强度与构件整体强度协调对提升复式空心钢管混凝土柱的抗爆性能尤为重要。最终建立了基于固端约束下复式空心钢管混凝土柱中挠度的超压-冲量(P-I)损伤准则及判定公式。     

考虑面力作用的HFR-LWC梁抗爆试验研究

实际工程中,面力作用会导致梁板构件的承载力提高以及破坏模式改变。为确切把握面力作用在爆炸加载全过程的变化规律及其对结构抗力的影响,该文进行了混杂纤维轻骨料混凝土（HFR-LWC）梁抗爆性能试验研究,得到爆炸荷载超压时程曲线及梁跨中位移、破坏模式等试验数据,结合端部约束刚度计算方法分析了面力作用对HFR-LWC梁抗力及破坏形态的影响规律。结果表明:试验装置可以合理模拟爆炸加载过程中梁构件的面力作用,是一套定量评估面力贡献的有效工具。面力作用能有效阻止纵向钢筋过早进入屈服状态,充分发挥混凝土的抗压性能,抑制裂缝的开展,有效减小梁的跨中位移,从而提高HFR-LWC梁的抗爆能力。     

外置可更换耗能器的预制拼装自复位桥墩抗震性能试验研究

基于抗震韧性设计理念,结合装配式结构技术,发展了具有外置可更换耗能器的自复位预制拼装桥墩结构。开展了两组自复位预制拼装桥墩模型结构的拟静力往复加载试验研究。介绍了往复加载过程中自复位预制拼装桥墩的受力行为及损伤过程,分析了其力-位移滞回曲线、骨架曲线、耗能能力、预应力筋张拉力变化、残余位移、接缝开口、墩底受压区高度等抗震性能。结果表明:外置耗能部件具有良好的可更换性和耗能能力,更换前后桥墩的抗震性能基本一致。自复位桥墩力-位移滞回曲线呈现出明显的"旗帜"型形态,残余位移较小,具有良好的自复位能力。随墩顶水平位移增加,墩柱内轴向预应力筋张拉力基本呈线性增加,更换耗能器后预应力筋的预应力损失减小。墩底外包钢管有效地抑制了局部混凝土压溃,钢管没有出现局部外鼓等损伤破坏。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

The Influence of Nitrogen and Boron Implant into Silicon Substrate on the Phase and Internal Stress of c-BN Films

Cubic boron nitride(c-BN) film was deposited on a Si (100) substrate by the RF-magnetron sputtering.The mainly problems for fabrication of c-BN films are the low purity and high intrinsic compressive stress. In order to solve the two problems, the c-BN film with the buffer interlayer was deposited on the substrate which had been implanted with nitrogen and/or boron ions. The results show: the implantation of nitrogen ions can obviously increase c-BN content and reduce the internal stress slightly; while the implantation of boron shows no obvious improvement to the content of c-BN, which can reduce the internal stress in the film obviously. In addition, it is suggested that the implantation of nitrogen and boron shows the best result, which not only can increase the content of c-BN, but also reduce the internal stress in the c-BN film obviously.