十字开槽爆破片超高压爆破实验与仿真研究

为了研究爆破片在瞬态超高压作用下的破裂形态和破裂压力等动态特性,设计了一种十字开槽爆破片,并通过实验和数值仿真相结合的方法进行了研究。首先,搭建了CO_2爆破试验平台对爆破片进行瞬态升压加载实验,得到了爆破片的破坏形态及破裂压力值;然后建立了基于Johnson-Cook损伤本构的十字开槽爆破片瞬态升压破裂失效的有限元模型,对破裂失效规律进行了分析。结果表明失效模式主要为十字中心破口,破裂形态、破裂压力和破裂时间与实验结果吻合良好,相对误差在6%以内;同时对十字开槽爆破片的有效厚度、槽深、槽宽等破裂压力的影响因素进行了仿真分析,得到破裂压力随有效厚度的增加而线性增大,随槽深的增加先下降后增大,随槽宽增加而成指数函数关系增大等规律。研究成果可为瞬态超高压力作用下的爆破片设计及工程应用提供参考。     

薄壁罐气压胀形参数优化研究

为提高金属薄壁罐气压胀形的成形质量,减少壁厚减薄严重及皱折破裂等成形缺陷,采用数值模拟的方法,分析了摩擦因数、模具圆角半径、坯料厚度、胀形压力对壁厚减薄率、最大应力值、轴向收缩的影响规律,试验验证与数值模拟结果吻合。研究结果对工艺优化和过程控制具有实用意义。     

侵彻过程中弹体内缓冲材料缓冲特性的数值模拟

为了研究战斗部侵彻过程中弹体内缓冲层对冲击应力的缓冲性能,采用动力学计算软件AUTODYN程序对不同材料的缓冲特性进行了数值模拟。结果表明:缓冲层的厚度影响其缓冲效果。厚度为1cm时,缓冲材料的缓冲能力顺序为:尼龙聚四氟乙烯铝合金1100纯铝有机玻璃聚氨酯。厚度为3cm时,缓冲能力顺序为:铝合金1100聚四氟乙烯尼龙纯铝聚氨酯有机玻璃;缓冲层的缓冲作用主要用于对应力波峰值压力的削弱,最为理想的缓冲材料应对应力波的弥散效应显著。     

聚脲涂层对装甲钢板抗爆性能影响的试验与数值分析EI北大核心CSCD

为研究聚脲涂层喷涂位置及涂层厚度对钢板抗爆性能的影响规律。对4种不同类型喷涂结构及纯钢板结构进行2 kg TNT(trinitrotoluene)炸药爆炸试验,并采用LS-DYNA仿真软件对试验工况进行数值模拟,比对试验结果验证数值计算的可靠性,同时在理论层面对迎、背面喷涂结构中的应力波衰减特性进行计算分析;在此基础上,进一步研究涂层厚度对背面喷涂结构抗爆性能的影响规律。结果表明:相比于无喷涂、迎面、双面喷涂结构,背面喷涂展现出更显著的抗爆潜力,其形成的大阻抗比结构是有效衰减应力波峰值的重要原因;等钢板厚度条件下,增加涂层厚度能有效提升结构抗力,但提升程度随着聚脲/钢板厚度比的增加而不断降低;等面密度条件下,增加涂层厚度结构呈现加剧破坏趋势。     

节理岩体爆破的破裂规律分析

通过实验室节理岩体模拟模型的电测实验,分析了节理岩体内爆炸应变波的传播规律及破裂形式,并与数值计算的模拟结果相比较,研究节理岩体爆破能量的耗损,为提高节理岩体的爆破效果提供理论依据。     

相控阵超声绝对声时法测量底面开口裂纹

针对工件内表面开口裂纹单面单侧定量检测困难的问题,采用相控阵超声绝对声时法(Absolute Arrival Time Technique,AATT)从单面单侧对不同厚度试块中的底面人工开口裂纹自身高度测量进行了数值仿真和实验,并对焊缝中的自然裂纹进行了AATT测量。对比AATT测量结果与常规衍射时差法超声检测(Time of Flight Diffraction,TOFD)测量结果并分析,发现AATT从单面单侧对底面开口裂纹进行定量测量可以达到与常规TOFD同样的测量精度。AATT操作简便,可单面单侧定量测量2 mm以上底面开口裂纹的自身高度。     

铝内胆复合材料储氢瓶爆破压力与疲劳寿命关系研究

针对在铝内胆复合材料储氢瓶（又称为“III型储氢瓶”）设计阶段难以根据设计的气瓶爆破压力和疲劳寿命确定内胆厚度和纤维应力比的问题,研究了III型储氢瓶爆破压力与疲劳寿命的关系。首先,构建了III型储氢瓶的有限元计算模型,提出了基于有限元的气瓶爆破压力和疲劳寿命的预测方法,分析了在内胆厚度和纤维应力比两个因素影响下III型储氢瓶的应力分布状态。其次,研究了内胆厚度和纤维应力比对III型储氢瓶爆破压力和疲劳寿命的影响规律,结果表明：在一定的内胆厚度和纤维应力比范围内,增大内胆厚度,气瓶爆破压力提升较小;增大纤维应力比,则气瓶爆破压力提升较大;III型储氢瓶对数疲劳寿命与内胆厚度和纤维应力比均基本呈线性关系。最后,基于纤维缠绕压力容器爆破压力计算公式和III型储氢瓶对数疲劳寿命拟合关系式,得到了不同条件下III型储氢瓶爆破压力与疲劳寿命的关系式。研究结果可为III型储氢瓶结构的优化设计提供参考。     

钢管混凝土柱-双面组合作用梁框架节点抗震性能试验研究

为了研究钢-混凝土双面组合作用梁框架节点的抗震性能,设计了3个钢-混凝土双面组合作用梁十字形框架节点和1个普通钢-混凝土单面组合作用梁十字形框架节点,并对其进行低周往复加载试验,对比分析其破坏模式、极限承载力、初始刚度、耗能能力、延性、刚度退化等抗震性能指标;通过改变下部混凝土板厚度和传力方式,研究下部混凝土板不同厚度和不同传力方式对双面组合作用梁力学性能的影响。结果表明:与普通钢-混凝土单面组合作用梁框架节点相比,钢-混凝土双面组合作用梁十字形框架节点具有更高的承载力和刚度,适用于荷载较大的结构,但在延性、刚度退化和耗能能力等方面无明显优势;下部混凝土板采用集中传力和均匀传力的方式对双面组合作用梁抗震性能的影响无明显区别;下部混凝土板采用预制法制作和螺栓连接更加方便、可靠。     

高能气体冲击载荷作用下高压容器仓排放孔膜片损伤模式及机理研究

针对高压容器仓内高能爆炸气体对排放口膜片结构毁伤模式无法准确有效预估,常出现提前破膜和不破模危险情况,进而对含预制损伤孔洞Q235钢结构膜片在爆炸冲击载荷作用下的宏细观损伤特性进行研究。基于高压爆炸装置,对含预制损伤孔洞Q235钢结构膜片抗爆毁伤效应进行一系列试验研究,结合试验研究结果,探索七孔枪药爆炸冲击载荷能量释放行为与相关参量之间的量化关系,进而为膜片毁伤机理研究提供理论依据,并建立膜片损伤孔洞尺寸与爆炸冲击载荷峰值压力之间的联系规律,最后,基于J-C模型的动态本构关系及失效准则对膜片破坏模式进行数值模拟研究。结果表明,随着爆炸冲击载荷压力地不断增大,含预制孔洞损伤膜片主要呈现均匀性损伤孔洞、边缘性应力集中撕裂、以及剪切冲塞等宏观损伤模式;建立的能量释放关系、以及含预制损伤膜片损伤孔洞尺寸与爆炸峰值压力之间地内在关联为多尺度损伤机理研究提供了量化依据;数值模拟中的膜片破坏形态及损伤孔洞尺寸与试验结果基本吻合,该数值模拟研究可为多尺度试验研究提供借鉴。     

电磁胀形磁场力的有限元分析

研究电磁胀形过程中工件受到的磁压力沿长度方向和厚度方向的分布是工件变形分析的基础。采用有限元方法对电磁胀形过程中作用工件上的磁场力进行了数值模拟。在磁场特性理论分析的基础上确立了模型的边界条件，得到了磁场力沿工件长度和厚度方向的分布规律。模拟结果与测量值基本吻和。     

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.     

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...     

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.     

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.     

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 ...