共查询到20条相似文献,搜索用时 78 毫秒
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由于焊接热过程的作用,焊接接头较容易产生组织性能劣化、残余应力、应力集中以及各种焊接缺陷。焊接缺陷的存在严重影响了焊接结构件的质量和安全使用,因此对含缺陷焊接接头进行安全性评估具有重要的工程应用价值。基于综合考虑含缺陷焊接接头的缺陷检测手段和BS 7910缺陷规则化表征处理的方法,对BS 7910中失效评估图的级别以及相应级别下针对含缺陷焊接接头评估点坐标确定过程中所涉及的应力种类和修正因子进行探讨,为工程实际利用BS 7910对焊接接头进行评估时的缺陷检测手段选择、缺陷规则化表征处理以及失效评估图级别的选择、评估点坐标的确定提供参考。 相似文献
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R60702焊接过程中容易出现气孔和氧化等缺陷,缺陷的产生与原材料和焊接工艺有直接关系。因此,通过对材料的焊接性进行分析,选择合适的焊接材料和焊接工艺,注重焊前处理、焊中保护和焊后处理,使焊接接头满足使用要求。 相似文献
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低合金高强度钢压力容器焊接的质量控制 总被引:3,自引:0,他引:3
介绍低合金高强度钢压力容器焊接过程和焊后常出现的缺陷,分析其产生的因素,并从焊接前准备、焊接过程、焊接后检验三个方面对低合金高强度钢压力容器焊接接头的质量进行控制。 相似文献
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氨制冷系统中压力管道是特种设备安全监管的核心,管道的焊接接头质量将直接影响整个氨制冷系统的运行安全。对氨制冷压力管道焊接接头进行缺陷及显微组织检测,分析焊接缺陷产生的原因以及对氨制冷管道服役安全造成的危害,并提出提高氨制冷管道焊接质量的建议。 相似文献
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《机电产品开发与创新》2015,(5)
论文针对了奥氏体不锈钢的焊接特点及易出现的焊接缺陷,主要介绍了对应用在低温环境下的奥氏体不锈钢焊接时,在不增加焊接接头中铁素体体积含量的前提下,如何采取措施防止焊接接头产生热裂纹,从而保证其接头的低温韧性。 相似文献
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1引言随着工业的发展,一些具有特殊性能的有色金属广泛地应用于制造压力容器。但是,这些有色金属在焊接过程中容易产生一些缺陷,特别是气孔,而气孔的存在会大大降低焊接接头疲劳强度,甚至无损探伤检查不出的小气孔对疲劳强度都会产生明显的不利作用。实验表明,气孔能使接头疲劳强度降低一半甚至四分之三。有鉴于此,必须分析这些有色金属焊接易产生气孔的原因,从而采取相应的措施加以防范。2造成工业纯钛焊接气孔的主要原因气孔是工业纯钛焊接时最常见的焊接缺陷,往往在熔合线附近形成。而这些气孔的形成主要是氢引起的。因为氢在钛… 相似文献
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Using single-molecule force-clamp spectroscopy, where the distance between the AFM tip and the sample surface is fixed and a few parallel avidin-biotin complexes are kept stretched by a certain force, we were able to observe the formation of single avidin-biotin bonds. Perspectives to use such an approach to study association reactions at single-molecule level in the conditions resembling those characteristic for some processes in vivo (e.g. virus-cell membrane attachment) are briefly discussed. 相似文献
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The near-field images calculation method for semiconductor surface with inhomogeneous electron distribution, formed by strong focused laser pulse, was proposed. Calculation is performed using Green function method. The main characteristic of the proposed approach is maximal usage analytical computations. The near-field images for the surface of GaAs were obtained at different points of time. Developed approach is universal and could be able to find with experimental data on time-resolved near-field microscopy some parameters of semiconductor surface such as diffusion constant and relaxation time. 相似文献
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General three-dimensional image simulation and surface reconstruction in scanning probe microscopy using a dexel representation 总被引:1,自引:0,他引:1
The ability to image complex general three-dimensional (3D) structures, including reentrant surfaces and undercut features using scanning probe microscopy, is becoming increasing important in many small length-scale applications. This paper presents a dexel data representation and its algorithm implementation for scanning probe microscope (SPM) image simulation (morphological dilation) and surface reconstruction (erosion) on such general 3D structures. Validation using simulations, some of which are modeled upon actual atomic force microscope data, demonstrates that the dexel representation can efficiently simulate SPM imaging and reconstruct the sample surface from measured images, including those with reentrant surfaces and undercut features. 相似文献
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介绍了利用ASP.NET技术开发一套基于B/S模式的数字现场工艺纪律管理系统的方法,实现了对现场工艺纪律的数字化和动态化管理。同时对系统的体系结构、功能特点和技术难点进行了介绍。 相似文献
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The use of flared tip and bi-directional servo control in some recent atomic force microscopes (AFM) has made it possible for these advanced AFMs to image structures of general shapes with undercut surfaces. AFM images are distorted representations of sample surfaces due to the dilation produced by the finite size of the tip. It is necessary to obtain the tip shape in order to correct such tip distortion. This paper presents a noise-tolerant approach that can for the first time estimate a general 3-dimensional (3D) tip shape from its scanned image in such AFMs. It extends an existing blind tip estimation method. With the samples, images, and tips described by dexels, a representation that can describe general 3D shapes, the new approach can estimate general tip shapes, including reentrant features such as undercut lines. 相似文献
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以A.C.C1eland公式为基础,实现了氨双级压缩制冷循环最佳中问温度的计算机求解,并给出了多种工况下的最佳中间温度的结果。 相似文献
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本文研究了二氧化硅和石墨或MCA粒子双分散型两相(液—固)润滑剂的摩擦磨损特性,这种双分散型的两相润滑剂的抗磨性能均较基础油为优。其中二氧化硅和石墨双分散型的几种油样的抗磨性能极其近似,说明抗磨性能与粒子含量无关。其摩擦系数随载荷的提高而显著下降,但达到一定的临界载荷值后,又趋于平稳,根据这些实验现象,笔者着重研究了双分散型润滑剂不同种粒子的协同作用方式,建立了相应的物理模型,并以此模型来分析实验现象产生的机理。 相似文献
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Novel carbon nanosheets as support for ultrahigh-resolution structural analysis of nanoparticles 总被引:1,自引:0,他引:1
Nottbohm CT Beyer A Sologubenko AS Ennen I Hütten A Rösner H Eck W Mayer J Gölzhäuser A 《Ultramicroscopy》2008,108(9):885-892
The resolution in transmission electron microscopy (TEM) has reached values as low as 0.08 nm. However, these values are not accessible for very small objects in the size range of a few nanometers or lower, as they have to be placed on some support, which contributes to the overall electron-scattering signal, thereby blurring the contrast. Here, we report on the use of nanosheets made from cross-linked aromatic self-assembled monolayers as TEM sample supports. When transferred onto a copper grid, a single 1.6-nm-thick nanosheet can cover the grid and is free standing within the micron-sized openings. Despite its thinness, the sheet is stable under the impact of the electron beam. Micrographs taken from nanoclusters onto these nanosheets show highly increased contrast in comparison to the images taken from amorphous carbon supports. In scanning transmission electron microscopy with nanosheet support, a size analysis of sub-nanometer Au clusters was performed and single Au atoms were resolved. 相似文献
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The three-dimensional Fourier filtering method and Schiske's Wiener filtering method are compared with the aim of high-resolution wave field reconstruction of an unstained deoxyribonucleic acid (DNA) molecular fiber using a through-focus series of images taken under a limited electron dose. There were some definite differences between the two reconstructed images, although the two kinds of processing are essentially equivalent except for the dimension and the filter used for processing. Through theoretical analyses together with computer simulations, the differences were proved to be primarily due to specimen drift during the experiment. Although the observed structure of the DNA molecular fiber was heavily damaged by electron beam irradiation, reconstructed images by the three-dimensional Fourier filtering method provided higher resolution information on the molecular structure even when relatively large specimen drift was included in the through-focus series. In contrast, in Schiske's Wiener filtering method, the detailed information of the structure was lost because of the drift, although the reconstructed image showed a higher signal-to-noise ratio. The three dimensional Fourier filtering method seems to be more applicable for observing radiation-sensitive materials under an extremely low electron dose, because specimen drift cannot be completely avoided. 相似文献
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Fluctuation electron microscopy (FEM) is a quantitative electron microscopy technique in which we use the variance V of spatial fluctuations in nanodiffraction as a function of the diffraction vector magnitude k and real-space resolution R to detect medium-range order in amorphous materials. We have developed a model for V(k, R) from a nanocrystal/amorphous composite, which is an idealized form of the medium-range order in various amorphous materials found by previous FEM measurements. The resulting expression for V(k, R) as a function of the nanocrystal size, nanocrystal volume fraction, and the sample thickness connects the FEM signal to well-defined aspects of the material's structure, emphasizes the need for samples of controlled thickness, and explains in some cases the relative height of peaks in V(k). We give an example of interpreting FEM data in terms of this model using recent experiments on amorphous Al88Y7Fe5. 相似文献