Calibration of the Weibull stress scale parameter, σu, using the Master Curve

This work proposes that the Weibull stress scale parameter, σ_u, increases with temperature to reflect the increasing microscale toughness of ferritic steels caused by local events that include plastic shielding of microcracks, microcrack blunting, and microcrack arrest. The Weibull modulus, m, then characterizes the temperature invariant, random distribution of microcrack sizes in the material. Direct calibration of σ_u values at temperatures over the DBT region requires extensive sets of fracture toughness values. A more practical approach developed here utilizes the so-called Master Curve standardized in ASTM Test Method E1921-02 to provide the needed temperature vs. toughness dependence for a material using a minimum number of fracture tests conducted at one temperature. The calibration procedure then selects σ_u values that force the Weibull stress model to predict the Master Curve temperature dependence of K_Jc values for the material. At temperatures in mid-to-upper transition, the process becomes more complex as fracture test specimens undergo gradual constraint loss and the idealized conditions of high-constraint, small-scale yielding assumed in E1921-02 gradually degenerate. The paper develops the σ_u calibration process to incorporate these effects in addition to consideration of threshold toughness effects and the testing of fracture specimens with varying crack-front lengths. Initial illustrations of the calibration process for simpler conditions, i.e. 1T crack-front lengths, use the temperature dependent flow properties and a range of toughness levels for an A533B pressure vessel steel. Then using the extensive fracture toughness data sets for an A508 pressure vessel steel generated recently by Faleskog et al. [Engng. Fract. Mech., in press], the paper concludes with calibrations of both m and σ_u over the DBT region and assessments of the Master Curve calibration approach developed here.     

半导体与智能电网

四十年来,半导体行业一直处于信息技术变革的前沿,提供的技术让通信更加轻松,让商业更具效率,让消费者获得有用的信息,同时让人们的娱乐生活变得丰富多彩。这些例子随处可见。如今的最新手机拥有的功能比20世纪60年代充斥房间的IBM大型主机更加强大。医疗     

Soot concentration and temperature measurements in co-annular, nonpremixed CH4/air laminar flames at pressures up to 4 MPa

Laminar nonpremixed methane-air flames were studied over the pressure range of 0.5 to 4 MPa using a new high-pressure combustion chamber. Flame characterization showed very good flame stability over the range of pressures, with a flame tip rms flicker of less than 1% in flame height. At all pressures, soot was completely oxidized within the visible flame. Spectral soot emission (SSE) and line-of-sight attenuation (LOSA) measurements provided radially resolved measurements of soot volume fraction and soot temperature at pressures from 0.5 to 4.0 MPa. Such measurements provide an improved understanding of the influence of pressure on soot formation and have not been reported previously in laminar nonpremixed flames for pressures above 0.4 MPa. SSE and LOSA soot concentration values typically agree to within 30% and both methods exhibit similar trends in the spatial distribution of soot concentration. Maximum soot concentration depended on pressure according to a power law, where the exponent on pressure is about 2 for the range of pressures between 0.5 and 2.0 MPa, and about 1.2 for 2.0 to 4.0 MPa. Peak carbon conversion to soot also followed a power-law dependence on pressure, where the pressure exponent is unity for pressures between 0.5 and 2.0 MPa and 0.1 for 2.0 to 4.0 MPa. The pressure dependence of sooting propensity diminished at pressures above 2.0 MPa. Soot concentrations measured in this work, when transformed to line-integrated values, are consistent with the measurements of Flower and Bowman for pressures up to 1.0 MPa [Proc. Combust Inst. 21 (1986) 1115-1124] and Lee and Na for pressures up to 0.4 MPa [JSME Int. J. Ser. B 43 (2000) 550-555]. Soot temperature measurements indicate that the overall temperatures decrease with increasing pressure; however, the differences diminish with increasing height in the flame. Low down in the flame, temperatures are about 150 K lower at pressures of 4.0 MPa than those at 0.5 MPa. In the upper half of the flame the differences reduce to 50 K.     

企业如何规避言行不一的陷阱

避开言行不一的陷阱的方法是：听其言，观其行，积极了解多方情况，认真观察实际情况     

Fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse quasicrystals

We report a numerical method to analyze the fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse (2-D TM) structures. The far-field diffraction patterns of the 2-D TM structures can be obtained by the numerical method, and they have a good agreement with the experimental ones. The analysis shows that the fractal characteristics of far-field diffraction patterns for the 2-D TM structures are determined by the inflation rule, which have potential applications in the design of optical diffraction devices.     

迎接当今包处理的挑战

用户对激动人心的全新网络服务的需求,正在推动网络带宽和数据流量的增长.作为回应,网络正在向更有效的以包为基础的模式发展,这种模式使网络能够为用户提供其需要的服务,并开发出额外的收入来源.网络设备制造商必须掌握包处理技术,才能提供新的服务,从而应对不断增加的网络复杂性及适应不同网速的要求.     

驱动白色LED背景照明的微型稳压器

查询号：１９０ 引言 手持信息家电中彩色ＬＣＤ显示的出现引发了对微型、明亮的白色背景照明的需求。幸运的是最近商品化的高亮度白色ＬＥＤ能提供理想的解决方案。这些微型ＬＥＤ能提供充足的白色光而没有脆度问题和通常用在笔记本计算机中的荧光背景照明有关的成本问题、然而,它们却有一个问题白色ＬＥＤ的正向电压可高达４Ｖ,这不能直接用单节锂离子电池为它们供电。 本文描述了升压和调节锂离子电池电压为白色ＬＥＤ供电的几种不同电路。这些电路能为驱动多个白色ＬＥＤ提供足够的功率并且足够小,适合于蜂窝电话和掌上计算机应用。 …     

Subnanometer Analysis and Modeling of MBE Grown InP Based MODFETs

InGaAs/InAlAs double-doped double-strained modulation-doped field-effect transistors OD-SMODFETs)1 were grown by solid source molecular beam epitaxy. The structures were characterized using high resolution x-ray diffraction, Hall effect, and cross-sectional scanning tunneling microscopy. A record two-dimensional electron gas (2DEG) sheet density of 8.5 × 10¹²/cm² and 8.1 × 10¹²/cm² for 300 and 77K, respectively, was achieved. The mobility was 6500 and 12000 cm²/ Vs for 300 and 77K, respectively. To the author’s knowledge,² the previous record 2DEG result was 6.58 × 10¹²/cm². The electron mobility was limited by alloy scattering and interface roughness caused by the presence of “clustering.” Using cross-sectional scanning tunneling microscopy to verify the presence of these clusters, we have the first images of the lattice matched InAlAs (spacer)-InGaAs (quantum well) interface. These images reveal clusters that have approximate spherical or cylindrical shapes with equivalent cubic dimensions ranging from 25 to 45Å.     

可增强压电加速计的电流仪表放大器

典型的压电传感器包含一片PZT-5A陶瓷材料的圆盘,在其表面有金属化电极.把导电环氧树脂涂到电极上,就可把外部导线连到传感器.绝缘粘合剂把组件连到待测结构,并把传感器和接地参考电位隔离开.圆盘面朝预期加速方向.