晶须及颗粒增韧氧化铝基陶瓷复合材料的抗热震性能

对Ａl2O3-SiCw和Ａl2O3-TiCp陶瓷基材料的抗热震笥能进行测试和分析,结果表明：Ａl2O3-SiCw和Ａl2O3-TiCp陶瓷在复合材料基体相比抗热震性能均有较大幅度的提高,其中,Al2O3-SiCw复合材料显示出更为优越的抗裂纹扩展能力与抗循环热震性能,材料增韧效果的差异是产生这一现象的主要原因。     

压痕-急冷技术表征Co 包覆Al2O3/TiC 复合材料的抗热震性能

采用压痕-急冷技术测试了Al2O3／TiC（AT）和Co包覆Al2O3／TiC（ATC）两种复合材料的抗热震性能．实验结果表明，ATC复合材料的抗裂纹扩展能力与抗循环热震性能都优于AT，ATC的临界温差△正比AT高25℃．诸抗热震参数R、R^I、R^IV和Rst的计算结果也表明，ATC的抗热震断裂能力和抗热震损伤能力均高于AT．少量Co的添加，虽然对ATC复合材料的热物理参数改变很小，甚至可以忽略，但却大幅度提高了复合材料的抗弯强度和断裂韧性，因而ATC具有较高的抗热震参数．ATC复合材料较好的抗热震性主要是其较高的抗弯强度及断裂韧性的贡献．     

Fe3Al(p)/Al2O3陶瓷基复合材料的抗热震性能

采用热压烧结制备了Fe3Al(p)／Al2O3复合材料，通过分析R曲线与热应力强度因子K曲线的相关性，对Fe3Al(p)／Al2O3复合材料抗热震性能进行分析预测．结果表明，理论预测与采用淬冷强度法得到的实验结果吻合较好，Fe3Al的加入使复合材料的抗热震性能明显改善，△Tc由单相的200℃提高至复合材料的→400℃，复合材料较单相Al2O3高的断裂韧性、导热率、及低的弹性模量和，(p)是导致其抗热震性能提高的主要原因。     

压痕-急冷法测定增韧氧化铝基陶瓷复合材料的抗热震性能

采用压痕-急冷法测试了Al2O3-SiCw，Al2O3-ZrO2和Al2O3-TiCp三种陶瓷基复合材料的抗热震性能，并与急冷强度法测试结果进行了对比分析。实验结果表明，两种方法之间存在一致性。三种陶瓷基复合材料与基体Al2O3相比抗热震性均有较大幅度的提高，其中Al2O3-SiCw复合材料显示出最为优越的抗裂纹扩展能力与抗循环热震性能。材料的增韧效果是产生这一现象的主要原因。压痕-急冷法与急冷强度法相比免去了热震后的强度测试，具有使用试样数目少，数据具有统计效应，可直接观测裂纹扩展等优点。     

反应烧结Si_3N_4的热震断裂行为

研究了四种 Si_3N_4材料的热震断裂行为。分析了材料的断裂参数(K_(1c)、γ(?) 和 σ(?))与抗热震参数之间的关系。无掺杂的 Si_3N_4-B_0的临界抗热震温差ΔT_c 为400℃左右,其热震裂纹以准静态的方式扩展。含 BN 的 Si_3N_4-B_1,Si_3N_4-B_2和 Si_3N_4-B_2材料的临界抗热震温差较高(ΔT_c=500℃),并在该温度点发生动态的裂纹扩展。当热震温差进一步提高,BN 含量较高的 Si_3N_4-B_2以及含有 BN 和 C 的 Si_3N_4-B_3在一定的温差增量范围内(ΔT_c′-ΔT_c=200℃)保持了裂纹的稳定;然后随着温差的继续扩大,其裂纹又逐步扩展。BN 含量较低的Si_3N_4-B_1则不同,其热震裂纹在作了动态扩展之后紧接着再逐步扩展。在实验的基础上阐明了 Si_3N_4材料的热震断裂行为是由抗热震参数控制的,而抗热震参数是断裂参数的函数。指出 Si_3N_4-B_2是适用于力学和热学环境下的结构材料,因其具有较高的抗热震参数和较小的热震强度衰减率。     

等离子弧喷涂Al2O3陶瓷涂层低温抗热震性能的研究

为研究等离子弧喷涂Al2O3陶瓷涂层的低温抗热震性能,对不同结构的涂层进行了600 ℃低温热震试验,并分析、探讨了涂层的热震失效机制.结果表明,Al2O3陶瓷涂层低温下热震失效是由层间裂纹或层内裂纹引起的.对于单一Al2O3涂层,涂层与基体的界面是最薄弱处,层间裂纹的萌生及扩展导致涂层自界面处脱落;对于有FeCrAl金属过渡层的涂层,层内粒子间的结合是最薄弱处,层内片层间裂纹的萌生、扩展导致涂层局部脱落.在陶瓷工作层与基体间增加金属过渡层可有效地缓和涂层界面处的热应力,阻碍裂纹的形成及扩展,从而提高涂层的抗热震性能.     

纳米Si3N4和喂料等离子处理对等离子喷涂Al2O3-YSZ涂层抗热震性能的影响

Si3N4可以提高Al2O3-ZrO2涂层的力学性能和抗氧化性能,但其对Al2O3-YSZ(Y2O3部分稳定的ZrO2)抗热震性能的影响未见报道.采用等离子喷涂的方法在304不锈钢表面制备了Al2O3-YSZ涂层.在喂料制备过程中加入纳米Si3N4,然后对添加和未添加纳米Si3N4的喂料进行等离子处理,研究纳米Si3N4和喂料等离子处理对涂层在800℃和1 000℃下抗热震性能的影响.采用扫描电子显微镜和X射线衍射仪分析了涂层热震试验前后的形貌及物相的变化.结果表明:喂料添加纳米Si3N4和等离子处理的综合作用显著地提高了涂层的抗热震性能;与喂料未添加纳米Si3N4且未经等离子处理的涂层相比,喂料添加纳米Si3N4且经等离子处理的涂层在800℃和1 000℃条件下的抗热震寿命分别提高了0.7倍和1.1倍;热震过程中涂层发生了α-Al2O3到γ-Al2O3的相变;在1 000℃下热震,涂层中形成了较宽的裂纹,涂层抗热震性能明显下降.     

碳纤维增强TiC复合材料的抗热震性能

通过测量力学性能和热物理性能,研究了热压烧结碳纤维增强TiC复合材料（Cf/TiC,20vo%碳纤维）的抗热震性能。结果表明,碳纤维加入到TiC基体中,提高了复合材料的抗弯强度和断裂韧性,降低了复合材料的弹性模量和热膨胀系数,进而使得复合材料的抗热震断裂参数R,抗热震损伤参数R^TV和裂纹稳定性参数RST都得以提高,复合材料热震残留强度在热震温差超过900℃后迅速下降。复合材料热扩散率的提高有利于抗热稳定性能的提高,复合材料增强机理是纤维承载。韧化机理是纤维桥联和纤维拔出。     

SiC/BN层状陶瓷的抗热震性能研究

采用水中急冷法研究了SiC/BN层状陶瓷的抗热震性能,并同SiC块体陶瓷作比较.实验结果表明SiC/BN层状陶瓷的热震断裂临界温差ΔTc为300℃,略低于SiC块体陶瓷的抗热震断裂临界温差.当热震温差ΔT >ΔTc 时,SiC/BN层状陶瓷的热震剩余强度的下降趋势明显比块体陶瓷的下降趋势缓慢.这同热震断裂和热震损伤理论计算的热震参数R和R的结果相一致.这表明:与SiC块体陶瓷相比,SiC/BN层状陶瓷的热震裂纹形核阻力略有降低,但热震裂纹扩展阻力却大大提高.分析认为BN弱界面对裂纹的吸收和偏转是材料断裂能提高的主要原因,断裂能的提高有利于材料热震阻力的提高.     

基于第一抗热震因子的BN纳米管/Si_3N_4复合材料抗热震性能评价

利用Kingery抗热震断裂理论构建了BN纳米管(BNNTs)强韧化陶瓷复合材料的第一抗热震因子模型,通过真空热压烧结法制备了四组BNNTs含量分别为0.5wt%、1.0wt%、1.5wt%和2.0wt%的BNNTs/Si_3N_4复合材料,并采用水浴淬冷法和三点弯曲法测试了复合材料的抗热震性能(震后弯曲强度和临界热震断裂温差)。测试结果验证了在急剧加热和急剧冷却条件下第一抗热震因子模型的正确性。结果表明:添加BNNTs使BNNTs/Si_3N_4复合材料第一抗热震因子增大,抗热震性能提升。分布在晶界上的BNNTs起到裂纹钉扎、桥联和裂纹偏转作用,增加了裂纹扩展的阻力;纳米管孔隙的存在改变了裂纹扩展路径,提高了BNNTs/Si_3N_4的断裂韧度,从而有效提高了其抗热震断裂能力。     

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.     

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 ...