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增材制造成形件中位错的研究进展
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作者 田根 王文宇 +4 位作者 王晓明 赵阳 韩国峰 任智强 朱胜 《材料导报》 EI CSCD 北大核心 2024年第1期160-170,共11页
增材制造是通过逐层堆积的方法制造实体零件的一种革命性技术,其成形性能受成形工艺、微观结构、沉积路径等影响,其中,位错作为晶体微观结构中广泛存在的一种线缺陷,是决定金属性能的一个重要因素。为深层次理解增材制造性能影响的本质... 增材制造是通过逐层堆积的方法制造实体零件的一种革命性技术,其成形性能受成形工艺、微观结构、沉积路径等影响,其中,位错作为晶体微观结构中广泛存在的一种线缺陷,是决定金属性能的一个重要因素。为深层次理解增材制造性能影响的本质机制,需进一步了解增材制造成形件中的位错特点。本文基于近年来增材制造成形件中位错的研究成果,梳理了位错的起源、特征和密度,分析了位错对强度等性能的影响。与传统制造相比,增材制造成形过程中因固有的循环加热-冷却而造成的压缩-拉伸应力循环使得增材制造成形件中的位错具有独特的结构和性质。在塑性变形中,位错随应变变化明显,不同的初始位错影响成形件对应变的响应;增材制造成形件中测量的位错密度高于锻件或铸件,不同位置、不同形状的位错密度也存在一定的差异;位错强化是增材制造成形件中的主要强化作用,与此同时,在钢的成形件中,位错还可诱发马氏体相变,促使再结晶,另外还影响成形件的腐蚀、蠕变和氢脆等。 展开更多
关键词 增材制造 位错结构 位错特性 位错密度 位错强化
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Influence of Purity Degree on the Evolution the Mechanical Properties of Aluminium Commercial
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作者 Ahmed Hakem Y. Bouafia 《Journal of Chemistry and Chemical Engineering》 2012年第10期920-924,共5页
The influence of the purity degree of the commercial aluminium on the mechanical properties: elastic stress, tensile strength, Brinell hardness, resilience and elongation at break was investigated. It was found that ... The influence of the purity degree of the commercial aluminium on the mechanical properties: elastic stress, tensile strength, Brinell hardness, resilience and elongation at break was investigated. It was found that the first three resistance characteristics decrease with the growth of the purity of the material chosen to the detriment of two ductility characteristics that rise to the three states considered: crude of casting noted: F, Annealed noted: O, hardened noted : H1/4. Furthermore, it is important to note that the hardened and the annealed lead respectively to a considerable hardening and a considerable softening. This hardening and this softening of the material in question can be respectively associated with the increase in dislocation density and immigration impurity elements of dislocations. 展开更多
关键词 PURITY ALUMINUM properties MECHANICAL hardness.
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THE SPECIFIC CHARACTER OF LIMIT ERRORS IN CLOSE RANGE PHOTOGRAMMETRY
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作者 FENG Wenhao 《Geo-Spatial Information Science》 2001年第3期50-56,61,共8页
Close-range photogrammetry is to determine the shape and size of the object, instead of it's absolute position. Therefore, at first, any translation and rotation of the photogrammetric model of the object caused b... Close-range photogrammetry is to determine the shape and size of the object, instead of it's absolute position. Therefore, at first, any translation and rotation of the photogrammetric model of the object caused by whole geodesic, photographic and photogrammetric procedures in close-range photogrammetry could not be considered. However, it is necessary to analyze all the reasons which cause the deformations of the shape and size and to present their corresponding theories and equations. This situation, of course, is very different from the conventional topophotogrammetry. In this paper some specific characters of limit errors in close-range photogrammetry are presented in detail, including limit errors for calibration of interior elements for close-range cameras, the limit errors of relative and absolute orientations in close-range cameras, the limit errors of relative and absolute orientations in close-range photogrammetric procedures, and the limit errors of control works in close-range photogrammetry. A theoretical equation of calibration accuracy for close-range camerais given. Relating to the three examples in this paper, their theoretical accuracy requirement of interior elements of camera change in the scope of ±(0.005–0.350) mm. This discussion permits us to reduce accuracy requirement in calibration for an object with small relief, but the camera platform is located in violent vibration environment. Another theoretical equation of relative RMS of base lines (m S/S) and the equation RMS of start direction are also presented. It is proved that them S/S could be equal to the relative RMS ofm ΔX/ΔX. It is also proved that the permitting RMS of start direction is much bigger than the traditionally used one. Some useful equations of limit errors in close-range photogrammetry are presented as well. Suggestions mentioned above are perhaps beneficial for increasing efficiency, for reducing production cost. 展开更多
关键词 Close-range photogrammetry size form absolute position limit error specific character
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Characteristics of strong earthquake evolution around the eastern boundary faults of the Sichuan-Yunnan rhombic block 被引量:16
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作者 CHENG Jia LIU Jie +2 位作者 GAN WeiJun YU HuaiZhong LI Gang 《Science China Earth Sciences》 SCIE EI CAS 2011年第11期1716-1729,共14页
Based on the existing materials of fault segmentation,characteristic earthquakes,and their empirical relationships,we calculated the parameters of the fault segments,such as length,width,magnitudes of characteristic e... Based on the existing materials of fault segmentation,characteristic earthquakes,and their empirical relationships,we calculated the parameters of the fault segments,such as length,width,magnitudes of characteristic earthquakes,etc.Constrained by GPS velocity field,the slip rates of these fault segments in depth were inversed using the 3-D half-space elastic dislocation model.As not all of the recurrence periods and co-seismic displacements of characteristic earthquakes are known,we selected the fault segments with these two parameters known and calculated the accumulation rate of average co-seismic displacement,which shows the faults' slip rate in seismogenic layer.Then,the slip rate in depth was compared with that in seismogenic layer,the relationship between them was obtained,and this relationship was used to get the recurrence periods and co-seismic displacements of all fault segments.After the studies above,we calculated the co-seismic deformation field of all the earthquakes larger than M s 6.8 from AD 1700 one by one and inversed the potential displacement in the co-seismic deformation field.Then,we divided the potential displacement by the slip rate from GPS inversion to get the influences of these fault segments,added the influences into the elapsed time of the characteristic earthquakes,and obtained the earthquake hazard degree of all the segments we studied in the form of the ratio of elapsed time to recurrence period;so,we name the ratio as the Impending Earthquake Risk (IER).Historical earthquake cases show that the fault segment is in safety when the IER is less than 1 but in danger after the IER becomes larger than 1.In 2009,the IER is larger than 1 on the following segments,1.35 on the Tagong segment of Xianshuihe fault,1 on the Menggu-Dongchuan segment,1.04 on the Dongchuan-Xundian segment,and 1.09 on the Yiliang-Chengjiang segment of Xiaojiang fault. 展开更多
关键词 eastern boundary faults of Sichuan-Yunnan rhombic block fault segment characteristic earthquake recurrence period earthquake Interaction Impending Earthquake Risk
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