热轧H型钢柱侧向冲击试验研究

利用DHR9401落锤式冲击试验机完成了两种不同边界约束条件下的12个热轧H型钢柱侧向冲击试验,试验中利用动态应变仪记录了冲击力时程曲线,并获得了试件的破坏形态和残余变形量。试验结果表明:热轧H型钢柱强轴在侧向冲击荷载的作用下,固-简约束边界务件的试件以发生整体弯曲变形为主,翼缘下支垫刚性平台约束边界的试件以撞击部位的局部屈曲变形为主;边界条件对试件的冲击力时程有显著影响;随着冲击能的增大,试件的残余变形增大,两者之间基本呈线性关系;试件在试验过程中表现出良好的延性性能和抗冲击性能。     

格构式钢柱抗侧向撞击性能的试验研究

格构式钢柱常用于重型工业厂房的排架柱或高大的独立支柱,此类构件使用环境复杂性,极易遭遇侧向撞击荷载作用。为探明格构式钢柱的抗侧向撞击性能,利用DHR9401落锤式冲击试验机完成了6根格构式钢柱侧向撞击试验。试验中利用动态应变仪记录了不同冲击能作用下格构式钢柱的冲击力时程曲线,并获得了其残余破坏形态和塑性变形量。结果表明:格构式钢柱在侧向撞击荷载的作用下表现出良好的延性性能和抗冲击性能,其残余变形主要包括整体侧向弯曲变形和撞击部位的局部屈曲变形;其残余变形的变化与冲击能的变化呈线性关系。     

侧向冲击载荷作用下钢管混凝土梁动力响应的实验和理论研究

该文中对套箍系数分别为1、1.15和1.9的两端简支钢管混凝土梁在侧向冲击载荷作用下的动力响应进行了实验和理论研究。动载试验在DHR-9401落锤式冲击实验机上进行,实验中得到了试件破坏模态和冲击力时程曲线等特征量。进而基于实验研究结果,并考虑撞击时局部变形的影响,建立了局部变形和整体变形的关系,推导出钢管混凝土梁在低速冲击下整体变形的计算公式,其结果与实验结果较为吻合,并为临界破坏冲击能的计算提供了方法。     

冲击荷载下钢筋混凝土缺口梁破坏模式的试验研究

钢筋混凝土梁在使用过程中内部的微裂缝和缺陷逐渐衍生扩展导致混凝土发生开裂。冲击荷载下钢筋混凝土缺口梁的承载性能和能量耗散与无缺口梁明显不同。为了合理评估钢筋混凝土缺口梁的抗冲击性能,利用落锤冲击试验机对不同配筋率的钢筋混凝土缺口梁进行了动态三点弯试验。通过对比分析冲击过程中锤头冲击力、支座反力和跨中位移,探讨了冲击速度对钢筋混凝土缺口梁破坏模式、承载力和能量耗散的影响。试验结果表明：钢筋混凝土缺口梁的破坏模式随着冲击速度和配筋率的增大由弯曲破坏逐渐转变为弯剪破坏;弯曲/弯剪破坏模式下支反力最大值和静态抗弯/抗剪承载力的比值与冲击速度呈线性增长关系;将支反力-跨中位移曲线简化为平行四边形后分别建立了静态抗弯/抗剪承载力与冲击速度的经验公式,为合理评估钢筋混凝土缺口梁的抗冲击性能提供参考依据。     

主管受拉的K形圆管节点抗冲击性能试验研究EI北大核心CSCD

管节点是钢管结构的传力构件,在撞击、爆炸等突发事故中,节点可能因受到冲击荷载而被破坏,严重时甚至会引起结构坍塌。为研究不同主管径厚比以及初始受力状态对节点抗冲击性能的影响,本文采用落锤试验机对两组主管径厚比不同的K形圆管节点进行了抗冲击性能试验研究。每组3个试件,其初始受力状态分别为:主管及支管未施加初始轴力、主管施加轴拉力两支管同时施加轴压力、主管施加轴拉力两支管分别施加轴拉力和压力。基于试验结果,比较了国内外相关规范的冲击承载力确定方法。研究结果表明:所有节点的破坏模态均主要表现为主管顶部受冲击区域的凹陷破坏;冲击过程中,初始受力状态相同时,主管径厚比较大的试件的主管局部凹陷变形与横向变形分别增大了19%和3%,冲击力峰值降低8%,冲击持时增加11%;主管径厚比相同的试件中,主管及支管未施加初始轴力的试件的主管局部凹陷变形最小,冲击力最大,冲击持时最短;将冲击力时程曲线平台值作为抗冲击承载力较为合适。     

钢筋混凝土复合防护梁的抗撞性能研究

传统结构构件设计较少考虑碰撞效应,因此有可能因碰撞荷载而引起严重的冲击破坏。鉴于此,在前期提出的刚柔复合防护结构体系的基础上,针对钢筋混凝土复合防护梁的抗撞性能进行了分析研究。在数值模拟的过程中,分别考虑了无防护、刚性防护、柔性防护和刚柔复合防护四种不同的措施以及两端固支、两端铰支和一端固支一端铰支三种不同的梁端约束形式。通过观测钢筋混凝土梁的应变、位移、加速度和冲击力等参数,可评价相应的抗撞效果。数值结果表明,提议的复合防护体系效果最好,可以有效抑制受撞构件的冲击响应;同时,构件约束形式对抗撞性能的影响也是不容忽视的。     

线弹性土壤中埋设悬跨管道的屈曲分析

建立了两端埋设在线弹性土壤中的悬跨管道的屈曲方程。利用细长梁小挠度理论,建立了含有轴向压力的悬跨段和埋设段管道的弯曲控制方程。基于埋设段管道的刚度和变形特性,建立了符合悬跨段管道实际情况的边界条件。导出了悬跨段管道对称屈曲和反对称屈曲的屈曲载荷方程,通过数值求解给出了不同土壤刚度系数条件下悬跨段管道屈曲载荷。研究表明:悬跨段管道的屈曲载荷系数依赖于土壤刚度系数,简支梁模型只在特定的土壤刚度系数下适用于悬跨管道;在土壤刚度系数很大时,两端固支梁模型才能反映悬跨管道的屈曲特性。建议采用该方法进行埋设悬跨管道的屈曲分析。     

压实系数对内填砂卵石薄壁方钢管柱在冲击载荷下力学性能的影响分析

利用落锤冲击装置完成了不同压实系数下内填砂卵石薄壁方钢管柱侧向冲击试验,试验中记录了冲击力时程曲线,并获得了试件的破坏形态以及残余变形量。基于剩余承载力损伤评估准则,定义损伤度来判定冲击荷载下内填砂卵石薄壁方钢管柱损伤破坏程度,分析压实系数与柱损伤度的关系。试验结果表明:试件在侧向冲击荷载作用下,主要以局部破坏为主,并伴有一定量的整体弯曲变形;除了试件塑性变形中产生的塑性铰能消耗部分冲击能量外,内填砂卵石也能耗散一部分冲击能量,且压实越紧密,能量消耗越多,该组合柱表现出了较好的抗冲击性能;在一定压实系数范围内,损伤度随着压实系数增大出现先增大后减小的趋势,且砂卵石离散程度越小,损伤度的变化速率就越大。     

泡沫铝填充薄壁铝合金多胞板与单胞板吸能性能研究

为研究泡沫铝填充薄壁铝合金多胞板(MCP)与单胞板(SCP)的吸能能力,该文设计了6种不同截面的泡沫铝填充薄壁铝合金多胞板与1种单胞板,并基于非线性有限元软件LS-DYNA建立了相应的数值模型。对经典铝合金板耐撞击试验及泡沫铝夹芯板耐撞击试验进行了数值模拟,分析表明该数值模型能较好的模拟泡沫铝夹芯板在冲击过程中的撞击力、挠度和变形形态。基于此模型对比研究了不同因素下多胞板与单胞板的吸能特性,分析了其破坏模式和吸能机理,最后通过正交试验的方法分析了不同因素下的吸能效率以及多胞板最优截面类型的选取。结果表明：在面外冲击作用下,泡沫铝填充薄壁铝合金板的破坏模式为对称圆锥式破坏,冲击力-位移曲线和变形图显示其变形过程分为两个阶段：弹塑性变形阶段和回弹阶段;在发生相同位移时,18种不同参数的多胞板,其吸收的总能量(E)和比吸能(SEA)相对于单胞板都提高了400%以上,是一种更具吸能特性的板,可广泛应用于防护工程。     

曲梁缓冲器的大变形及变形能的椭圆函数解EI北大核心CSCD

金属曲梁结构在发生大变形情况下仍然具有良好的回弹性能,可以用作承受重复冲击系统的冲击能量吸收装置。针对由固支圆形曲梁组成的缓冲器,推导了基于半径和截面角的固支曲梁的大变形平衡方程。给出了端部压力及平板压力作用下曲梁的截面角、位形及变形能的Jacobi椭圆函数解,详细分析了简支圆形曲梁缓冲器的大变形特性及能量吸收特性。结果表明:曲梁缓冲器具有明显的非线性大变形特性和良好的缓冲吸能特性,其缓冲系数曲线有明显的极小值点;缓冲系数的极小值取决于曲梁材料、曲率半径及初始安装角度,与其数量无关。     

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.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

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.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

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.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.