Parametric study on buckling behaviour of dented short carbon steel cylindrical shell subjected to uniform axial compression

Generally, thin cylindrical shells are susceptible for geometrical imperfections like non-circularity, non-cylindricity, dents, swellings, etc. All these geometrical imperfections decrease the static buckling strength of thin cylindrical shells, but in this paper only effect of a dent on strength of a short (Lc/Rc∼1, Rc/t=117, 175, 280) cylindrical shell is considered for analysis. The dent is modeled on the FE surface of perfect cylindrical shell for different angles of inclination and sizes at half the height of cylindrical shell. The cylindrical shells with a dent are analyzed using non-linear static buckling analysis. From the results it is found that in case of shorter dents, size and angle of inclination of dents do not have much effect on static buckling strength of thin cylindrical shells, whereas in the case of long dents, size and angle of inclination of dents have significant effect. But both short and long dents reduce the static buckling strength drastically. It is also found that the reduction in buckling strength of thin cylindrical shell with a dent of same size and orientation increases with increase in shell thickness.     

Thermo-mechanical coupling in cylindrical bending of sandwich plates

This paper presents an exact solution of linear elasticity theory for bending of sandwich plate-like beams due to temperature difference at the plate faces. It is assumed that the heat flow is stationary. The exact solution yields the temperature profile, stress and displacement distribution across the plate thickness. The analytical results are complemented by an example of a simply-supported sandwich beam.     

物理学与计量学—21世纪的计量学

回顾物理学与计量滨发展历史，指出建立在经典物理学基础上的计量单位制存在的问题。分析２１世纪物理学的研究重点及其与计量学密不可分的关系，并讨论了高新技术的发展对量子计量学的需求，以及计量学对地社会安全与安定所起的重要作用。     

具有缺陷和应力限值的预应力钢支撑柱屈曲性能

通过预应力支撑加固的钢柱,一般增加了轴向抗压强度。过去,十分强调获得更高的临界屈曲荷载,然而,后屈曲性能是结构安全性和功能的重要保证。对具有几何缺陷和与可能的材料失效相关的应力极限的支撑柱的屈曲性能进行检验。考虑有几何缺陷支撑柱的屈曲性能,采用Rayleigh-Ritz方法对几何非线性模型公式化,并通过有限元方法进行验证。研究显示：对于承受最高临界荷载的预应力状态,系统对有几何缺陷的柱更为敏感。对某一给定形状结构,实际的最大荷载似乎随着预应力的增加而增加。研究建议：最佳的预应力取值应该大于基于传统方法的线性分析的结果。     

Optical measuring systems and technologies for some urgent tasks in industry and science

Modern industry and science take novel optical measuring systems and laser technologies with high resolution and productivity for solving actual tasks,including safety problems for mining,oil,atomic and railway in-dustries.The TDI SIE's results in these trends are presented.     

测量误差理论与术语定义的发展与变化

阐述了测量误差理论的发展历程与发展方向,回顾了与误差理论和数据处理相关的国家计量技术规范跟随国际计量技术规范发展的过程,分析了国家计量技术规范中主要误差术语定义的变化情况和变化趋势。术语定义的变化表明：术语变化的趋势更具有严密的科学性、逻辑性和可操作性。     

Sphere mass center determination by velocity modulation

This paper presents a new technique, called velocity modulation, for measuring the mass center location of a sphere, improving upon the accuracy of previous methods by at least a factor of 4. The sphere is rolled down a set of parallel rails. The offset of the sphere’s mass center with respect to its geometric center modulates the sphere’s velocity at the rolling frequency, which is detected by a series of differential optical shadow sensors. The measured times that the sphere crosses the sensors is compared with a simplified mechanics model in order to recover the sphere’s mass center location. The precision of the technique is demonstrated by the repeatability of independent measurements in one plane of a 50.8 mm (2 in.) stainless steel gage sphere. The best standard deviation achieved is 145 nm (95% confidence interval = 227 nm).     

液体闪烁核活度计量仪

本文描述用液体闪烁计数法直接测定α、β发射体溶液放射性活度的计量仪器。该仪器包括三个光电倍增管的符合探测器和三个输出计数道;以三重对两重符合计数率之比(TDCR)为猝灭参数,通过外推效率曲线至TDCR=1直接得到核素的活度。该仪器用于放射性活度绝对测量至少有两个突出的优点:1.精确度较高,对~3H、~(63)Ni和~(14)C等多种β、α核素其总测量不确定度(3σ)在0.5—1.5％;2.操作简便,测量迅速。     

Distortions induced in turbine blades by hot forging and cooling

Geometrical distortions of hot forged thin components are one of the main causes that force process designers to work with significant allowances. Their identification in the early stages of process design would permit changing the process parameters in order to compensate them during cooling after the hot forging process.This paper presents a novel approach to evaluate geometrical distortions of hot forged components characterized by complex and thin geometrical features, such as turbine blades. A thermo-mechanical–metallurgical model of both the forging and cooling phases is developed, in order to investigate the effects of different cooling rates after forging on the component final geometry and then to choose those cooling parameters that assure minimal distortions. The developed models are calibrated through extensive experimental campaigns, involving both laboratory experiments and on-field measurements during industrial productions. Thermal boundary conditions are identified through on-field measurements of blade surface temperatures, while material behaviour regarding flow stress determination and phase transformation-related parameters is obtained through compression and tensile tests with a dilatometer aid, all carried out in the range of temperatures of interest for the forging and the cooling phases.     

Quantification of tool wear using white light interferometry and three-dimensional computational metrology

Although several wear modes can result from machining, the most common tend to be what are referred to as flank wear and crater wear. Flank wear can be easily measured directly from images of a worn cutting tool, and this is the typical method used to quantify the condition of a tool. On the other hand, crater wear is difficult to quantify, and thus has typically been treated in a qualitative manner. The inability to characterize and compare the two wear modes in a quantitative way is an increasingly important problem as the precision of machining operations improves and cutting moves almost exclusively to the nose radius of cutting tools. This paper introduces a new approach to this problem by proposing a technique to quantify both wear modes for direct comparison. The technique measures the volumetric wear loss in the two regions by comparing three-dimensional wear data obtained by white light interferometry with ideal representations of unworn cutting tools. The resulting wear measurements are compared and related to changes in the cutting process, specifically increases in cutting forces and changes in the topography of machined surfaces.