碳纤维增强alpha-TCP/TTCP骨水泥的研究

制备了经过氧化处理的碳纤维增强磷酸钙骨水泥(a-tricalcium phosphate cement/tetracalcium phosphate, a-CP/TTCP), 初步探讨了碳纤维长径比、含量对硬化体抗压、抗折强度的影响.实验结果表明长径比为375, 添加量为0.3wt%时, 增强效果最为理想, 抗压强度提高了55%(最大为63.46MPa), 抗折强度提高近100%(最大为11.95MPa), 而掺入量太大及长径比太高, 碳纤维因不能均匀分散将限制其性能的发挥.生物学评价实验结果表明碳纤维增强的骨水泥具有良好的生物相容性.     

短切PAN基碳纤维水泥基复合材料的制备及性能研究

以硅酸盐水泥P.O 42.5为基础材料、短切PAN基碳纤维为增强相制备了分散均匀的碳纤维水泥基复合材料,研究了不同掺杂量(0,0.3%,0.6%和0.9%(质量分数))短切PAN基碳纤维的水泥基复合材料的物相结构、微观形貌、力学性能、耐磨性能和抗碳化性能。结果表明,短切PAN基碳纤维的掺杂加速了水化反应的进行,没有产生新的水化产物,碳纤维在水泥基复合材料中呈三维错落分布,构成网格结构,提高了水化产物之间的结合强度,提高了水泥基复合材料的致密性,从而提高了水泥基复合材料的力学性能、耐磨性能和抗碳化性能。随着短切PAN基碳纤维掺杂量的增加,水泥基复合材料7和28 d的抗压强度和抗折强度均表现出先增大后降低的趋势,而质量损失率和碳化深度则表现出先降低后升高的趋势。当短切PAN基碳纤维的掺杂量为0.6%(质量分数)时,质量损失率达到最小值0.34%,养护7和28 d后,抗压强度达到了最大值69.3和86.4 MPa,抗折强度也达到了最大值11.1和14.1 MPa,而碳化深度达到最低值0.35和2.53 mm。综合分析可知,短切PAN基碳纤维的最佳掺杂量为0.6%(质量分数)。     

聚乙烯醇纤维对盐冻混凝土抗折强度的影响

通过聚乙烯醇纤维增强混凝土(PVA-FRC)试件和素混凝土试件28 d弯曲抗折试验和300次盐冻后弯曲抗折试验,考察盐冻对混凝土试件弯曲抗折强度的损伤和纤维对盐冻前后混凝土试件弯曲抗折强度的增强作用.设置了3种纤维体积掺量的PVA-FRC试件,并在纤维体积掺量为1.5％的基础上,分别以10％硅灰和20％粉煤灰替代等量水泥试图提高PVA-FRC试件盐冻前后抗折强度.结果表明,PVA-FRC试件盐冻前后抗折强度均大于素混凝土试件盐冻前后抗折强度,纤维体积掺量为1.5％的PVA-FRC试件盐冻前后增益比最大;PVA-FRC试件盐冻后抗折强度损伤量远小于素混凝土试件抗折强度损伤量,纤维体积掺量为1.5％的PVA-FRC试件损伤量最低;硅灰和粉煤灰的掺加没有提高PVA-FRC试件盐冻前后的抗折强度,也没能降低PVA-FRC试件盐冻后抗折强度损伤量.     

超高性能磷酸镁水泥混凝土的制备和力学性能研究

磷酸镁水泥(MPC)凝结硬化速度快,早期强度高,采用MPC作为胶凝材料,有利于在无养护条件下制备出具有高早强特征的超高性能磷酸镁水泥混凝土(UHPMPCC)。研究了钢纤维掺量和长径比等参数对UHPMPCC物理力学性能的影响,分析了UHPMPCC中钢纤维的增强机制和影响规律。结果表明25 mm钢纤维有利于提高早期抗压强度,而13 mm钢纤维更有利于提高长期力学性能;13 mm钢纤维的掺量2.5%(体积分数)时,无养护的UHPMPCC6h抗压强度和抗折强度超过60和25 MPa, 28 d抗压强度和抗折强度超过120和38 MPa。MPC浆体早期呈酸性,使钢纤维表面产生刻蚀,鸟粪石嵌入钢纤维中,增强MPC基体和钢纤维的界面粘结,有助于提高UHPMPCC的抗弯强度。     

聚乙烯醇在高性能水泥基材料中的作用机理分析

为了探讨聚乙烯醇(PVA)在高性能水泥基材料中的作用机理,试验研究了在不同水胶比(W/B)和聚胶比(P/B)时,聚乙烯醇对抗压强度和抗折强度的影响,并通过红外光谱和X射线衍射分析了聚乙烯醇(PVA)粉体在高性能水泥基材料中的作用机理.试验结果表明:掺入适量的聚乙烯醇(PVA)可以明显提高高性能水泥基材料的强度,存在一个最佳的聚乙烯醇(PVA)掺量;在本试验条件下,在聚胶比(P/B)为2.5%时,强度最高,其抗压强度和抗折强度分别达到113.6MPa和23.0MPa;红外光谱和X射线衍射分析表明,聚乙烯醇(PVA)参与了水泥的水化,形成的化学键增强.     

碳纤维建筑节能保温砂浆的制备及其性能研究

为了获得优异保温性能和高强度的节能保温砂浆，以普通硅酸盐水泥P.O 42.5作为基质材料，通过在砂浆中添加适量的碳纤维作为增强材料，以此制备了碳纤维建筑节能保温砂浆，研究了碳纤维的掺杂量对保温砂浆的力学性能、收缩率及保温性能的影响，并建立了保温砂浆导热系数和表观密度的关系式。结果表明，随着碳纤维掺杂量的增大，保温砂浆的表观密度先降低后轻微升高，稠度、抗压强度和抗折强度均先升高后降低。在28 d龄期，当碳纤维的掺杂量为0.5%(质量分数)时，保温砂浆中网状结构的致密性最好，抗压强度和抗折强度均达到最大值，分别为46.1和6.8 MPa,其中抗折强度提高了23.64%,改善效果高于抗压强度。随着碳纤维掺杂量的增大，保温砂浆的收缩率持续降低，导热系数先降低后增大，当碳纤维的掺杂量为0.5%(质量分数)时，保温砂浆的导热系数达到最低值为0.0583 W/(m·K),保温性能最佳。通过拟合保温砂浆的导热系数和表观密度发现两者为线性相关，方程的拟合度为98.4%。综合可知，碳纤维的最佳掺杂量为0.5%(质量分数)。     

纳米碳纤维增韧水泥基复合材料的力学性能和耐久性能研究

以普通硅酸盐水泥P.O 42.5为基体材料,不同掺杂量(0,0.4%,0.8%和1.2%(质量分数))的纳米碳纤维为增强相,制备了纳米碳纤维增韧水泥基复合材料,研究了纳米碳纤维的掺杂量对水泥基复合材料晶体结构、力学性能和耐久性能的影响。结果表明,纳米碳纤维的掺杂在水泥基复合材料中未出现新的水化产物,但加速了水化反应的进行;纳米碳纤维的“连接”作用使水泥基复合材料的孔结构变得致密,裂纹和孔隙减少;随着纳米碳纤维掺杂量的增加,水泥基复合材料的抗压强度和抗折强度先增大后减小,当纳米碳纤维的掺杂量为0.8%(质量分数)时,水泥基复合材料28 d的抗压强度和抗折强度均达到了最大值,分别为82.4和13.1MPa;采用单面盐冻法对水泥基复合材料进行抗冻性能测试,发现纳米碳纤维的掺杂改善了水泥基复合材料的抗冻性能,当纳米碳纤维的掺杂量为0.8%(质量分数)时,水泥基复合材料在28次冻融循环后单位面积质量损失量最小为0.114 kg/m²。综合力学性能和耐久性能分析可知,纳米碳纤维的最佳掺量为0.8%(质量分数)。     

钢纤维形状与掺量对UHPC施工及力学特性的影响

选用四种平直及两种端钩钢纤维,研究钢纤维体积掺量、长径比、形状、同形及异形纤维混掺对超高性能混凝土(UHPC)施工及力学性能的影响.通过相关实验得到了UHPC扩展度、抗压强度、抗折强度、能量吸收、断裂能及弯曲应力-挠度曲线;基于弯曲应力-挠度曲线及改进后的规范方法计算了UHPC的弯曲韧性指标;最后,开展了最佳纤维混掺比例的研究.结果表明:纤维掺量每增加0.5％,UHPC扩展度平均降幅为2.72％,抗压强度平均增幅为5.79％.抗折强度、弯曲韧性指数和能量吸收则先增后减(临界掺量为3.5％),断裂能呈上下波动(在3％时达最低值).随着纤维长径比的增大,UHPC扩展度降低,抗压强度、抗折强度、弯曲韧性指数、能量吸收值和断裂能基本呈递增趋势.相同长径比时,端钩形纤维UHPC扩展度、弯曲韧性指数优于平直形纤维,抗压强度、抗折强度、能量吸收、断裂能低于平直形纤维.同形纤维混掺UHPC扩展度、抗压强度稍低于对应的单掺纤维,弯曲韧性、能量吸收、断裂能总体上优于单掺试件;异形纤维混掺UHPC扩展度、抗压强度稍低于单掺试件,抗折强度与单掺试件各有所长,弯曲韧性、能量吸收及断裂能绝大多数优于单掺纤维.UHPC抗折强度变异性高于其抗压强度.单掺和混掺纤维时,UHPC试件的抗压强度、抗折强度综合最优分别为173.53 MPa、44.9 MPa和160.9 MPa、55.72 MPa;纤维混掺最佳组合为18 mm平直形、16 mm端钩形,且两者混掺比例为1:1时,UHPC的综合力学性能较优.     

聚乙烯纤维对超高性能混凝土性能的影响

高强高模量聚乙烯纤维(PE纤维)是一种被广泛研究应用的新型合成纤维增强材料。系统地研究了不同掺量、不同长径比的PE纤维对超高性能混凝土(UHPC)性能的影响。结果表明PE纤维能显著提高混凝土的抗折强度和抗压强度,在纤维体积掺量为2%的情况下,抗折强度为28MPa,抗压强度为157MPa,较素UHPC分别提高了47.3%和28.1%。PE纤维的掺入大大提高了混凝土的韧性,改变了混凝土脆性破坏的形态,表现为多缝开裂,荷载-挠度全曲线表现为位移硬化。     

纳米碳纤维改性混凝土的力学性能及抗冻性能研究

纳米碳纤维凭借着高的抗拉强度和弹性模量，被广泛应用于水泥混凝土的增韧剂。通过在混凝土材料中掺入不同含量(0,0.3%,0.6%和0.9%(质量分数))的纳米碳纤维，研究了纳米碳纤维掺杂量对混凝土力学性能和抗冻性能的影响。结果表明，纳米碳纤维的掺杂未生成新的产物，但加速了水化反应的进行，增加了改性混凝土的结构致密性，减小了孔隙和缺陷的数量。当纳米碳纤维的掺杂量为0.6%(质量分数)时，改性混凝土的形貌结构最佳。随着纳米碳纤维掺杂量的增加，改性混凝土的抗压强度、抗折强度和磨损量降低比率先增大后减小，单位面积的磨损量和80次冻融循环时刻的质量损失率先减小后增大。当纳米碳纤维的掺杂量为0.6%(质量分数)时，改性混凝土28 d的抗压强度和抗折强度达到最大值，分别为47.83和5.92 MPa,单位面积的磨损量最小为1.12%,磨损量降低比率最大为55.56%,80次冻融循环时刻的质量损失率最小为1.23%。综合各分析可知，纳米碳纤维的最佳掺杂量为0.6%(质量分数)。     

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 ...