SENB 方法中 K_(1c)的修正与尺寸效应

单边切口梁(SENB)法是测试脆性材料断裂韧性 K_(?)的最通用而简便的一种方法,但它在理论上还不够完善。本文分析了试样尺寸对 K_(lc)测试值的影响,导出了不同尺寸比例试件的 K_(lc)之间的关系式。并发现对应于临界尺寸下 K_(lc)测试值是最大值,约为真实值的1.2倍。对氧化铝和氮化硅两种工程陶瓷进行了尺寸效应的试验,得到的结果与理论分析完全一致。     

BaTiO_3,VO_2和 BiSrCaCu_2O_y 陶瓷相变与 K_(1c)的关系

用切口梁三点弯曲法测定了高于和低于相变温度的 BaTiO_3,VO_2和 BiSrCaCu_2O_y 多晶试样的平面应变断裂韧性 K_(lc)。结果表明,对于这几种材料,如果由于不纯净或掺杂而在低于相变温度下仍有部分高温相残留,则其韧性将得到改善。本文讨论了这种改善的原因。     

碳纤维增强可切削金云母微晶玻璃复合材料的制备及其特性

金云母微晶玻璃 KMg_3[AlSi_3O_(10)]F_2是一种脆性、可切削的陶瓷材料,经碳纤维增强制成复合材料(CPMC)后,其脆性和力学性能得到显著改善,而可切削性能保持不变。实验结果证明:金云母基体的缺口弯曲强度 S_b=11.26MPa,断裂韧性 K_(lc)=0.24MPa·m~(1/2),断裂功 W_F=145.9(?),而含碳纤维5.56%的 CPMC,其 S_b=47.10MPa,K_(lc)=1.1MPa·m~(1/2),W_F=2133.2(J/(m~2)),二者相比提高4至14倍。     

Y_2O_3-ZrO_2胸瓷在循环应力作用下的疲劳特性

测定了三种 Y_2O_3-ZrO_2陶瓷的 S-N 曲线,并由此计算了其裂纹扩展参量。结果表明,应力腐蚀指数 n 与 K_(lc) 没有明显的对应关系。     

含表面裂纹焊接结构断裂影响因素的PFM分析与失效概率计算

以PFM理论为基础,对含表面裂纹焊接结构断裂影响因素进行了概率统计分析,并采用H-L法对结构失效概率进行了计算.结果表明,在以应力强度因子作为评定标准时,K(lc)、σ和α三个基本随机变量中,K_(lc)的变异对结构的失效概率影响最大.H-L方法简单实用,计算精度较高,在工程焊接结构的安全评定方面有较大的实用价值.     

摆锤刀刃半径对夏比V型冲击吸收能量的影响

为研究不同尺寸摆锤刀刃锤头对冲击试验结果的影响,采用刀刃圆角半径分别为2mm和8mm的锤头对多种材料进行夏比V型冲击试验,并从吸收能量、断口形貌等方面分析V型缺口试样在2mm摆锤刀刃下的冲击吸收能量K_(V2)与8mm摆锤刀刃下的冲击吸收能量K_(V8)的变化规律,研究摆锤刀刃尺寸对夏比V型冲击吸收能量的影响。结果表明:在韧脆转变温度曲线上平台区和转变区(塑性断口)范围内,K_(V8)大于K_(V2);在转变区(脆性断口)范围内,K_(V2)大于K_(V8);在下平台区,KV8与K_(V2)几乎相等。     

船舶螺旋桨叶片的疲劳强度研究(报告Ⅱ:螺旋桨叶片的容许缺陷尺寸和探伤范围)

为了检测船舶螺旋桨的内部缺陷,成功地发展了一种超声波检测缺陷的技术,当将这种技术应用于实际螺旋桨时,必須确定允許的缺陷尺寸,以及叶片需要加以检测的区域。本文已为达到此目的而提出了如下的分析和计算。 (1)用线弹性断裂力学和螺旋桨材料的⊿K_Φ值分析疲劳裂纹是否从桨叶的缺陷处进一步扩展。 (2)在干若种应力、桨叶厚度和纵横比条件下计算缺陷的最大容許尺寸。 (3)用不稳定升力面理论计算了螺旋桨上在尾件流区缺陷中的应力分布,根据每个螺旋桨的临界缺陷尺寸分布,确定出所要检测的区域。     

乙二醇溶剂热法制备K_(0.5)Na_(0.5)NbO_3陶瓷粉体

采用乙二醇溶剂热法制备K_(0.5)Na_(0.5)NbO_3陶瓷粉体,系统研究了V(EG)/V(H_2O)、反应温度、前驱液浓度对粉体物相、形貌及颗粒尺寸的影响。结果表明,反应温度230℃,反应时间7h,V(EG)/V(H2O)≤3∶2可获得纯相的K_(0.5)Na_(0.5)NbO_3粉体;温度升高粉体的结晶性变差;当溶液浓度为6mol/L时,粉体出现球形和正方体两种形貌,反应物浓度增大粉体均出现正方体形貌且颗粒尺寸减小,当浓度为10mol/L、V(EG)/V(H2O)=1∶4时,粉体颗粒尺寸最小。     

用紧凑试验评价结构钢脆性裂纹终止韧性

对于SA533BC1,1,HT80和KD32钢进行了如紧凑试验、ESSO试验和DCB试验之类的裂纹终止试验,以评价其裂纹终止韧性值。得到的主要结论如下: 1) 裂纹终止韧性是用对紧凑试验进行静态分析得到的K_(1a)予以评价的。 2) 用紧凑试验进行动态分析所确定的K_(1D)值大于K_(1a),但当K_(1a)/K_Q为1时K_(1D)接近于K_(1ao)K_Q是裂纹起始时的应力强度因子。 3) 由ESSO试验和DCB试验得到的K_(1a)和K_(ca)两者没有显著的差别,但在低温下由DCB试验得到的K_(ca)小于K_(1a)。 4) 在转变温度区,K_(1a)小于K_(1c)而大于K_(1do)在这个温度区,由J_(1c)确定的K_(1c)随温度的升高而降低并且小于K_(1a)。 5) 由2毫米夏比V型缺口冲击试验得到的断口形貌转变温度和吸收能是表示裂纹终止韧性的合理参量,而NDT温度却不是。     

用R-曲线法和伸张区宽度法评定HT80、SM50A及2017-T_4的断裂韧性J_IC值

用ASTM和JSMER-曲线法以及JSME伸张区宽度(SZW)法对两种钢和一种铝合金进行了J_(lc)试验。SZW法在延性撕裂起始时具有过高的评定J_(lc)的倾向。ASTM方法也具有过高地评定J_(lc)值的倾向,而且似乎是最简便和稳定的方法。JSMER-曲线方法给出最小的J_(lc)值,在物理上最接近开裂点。     

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.