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Accurate measurement of wall skin friction by single-pixel ensemble correlation

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Science China(Physics,Mechanics & Astronomy) 2014年第7期57卷 1352-1362页

作者： shen junqi PAN Chong WANG JinJun Fluid Mechanics Key Laboratory of Ministry of Education Institute of Fluid Mechanics Beijing University of Aeronautics and Astronautics

The present work deals with accurately estimating wall-skin friction from near-wall mean velocity by means of PIV *** estimation accuracy relies on the spatial resolution and the precision of the resolved velocity profile inside the viscous sublayer,which is a big challenge for conventional window-based correlation method(K?hler C J,et *** Fluids,2012,52:1641–1656).With the help of single-pixel ensemble correlation,the ensemble-averaged velocity vector can be resolved at significant spatial resolution,thus improving the measurement *** demonstrate the feasibility of this single-pixel ensemble correlation method,we first study the velocity estimation precision in a case of steady near-wall *** particle images are used to investigate the effect of different image *** is found that the velocity RMS-uncertainty level of the single-pixel ensemble correlation method can be equivalent to the conventional window correlation method once the effective particle number used for the ensemble correlation is large ***,a canonical turbulent boundary layer is synthetically simulated based on velocity statistics resolved by previous Direct Numerical Simulation(DNS)work(Schlatter P,et al.J Fluid Mech,2010,659:116–126).The relative error of wall skin friction coefficient is shown to be one-order smaller than that of the window correlation *** the optimization strategy to further minimize the measurement uncertainty is discussed in the last part.

关键词： skin friction measurement particle image velocimetry single-pixel ensemble correlation

Effects of Microalloying and Heat-Treatment Temperature on the Toughness of 26Cr–3.5Mo Super Ferritic Stainless Steels

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Acta Metallurgica Sinica(English Letters) 2014年第3期27卷 407-415页

作者： Li Ma Jian Han junqi shen shengsun Hu Tianjin Key Laboratory of Advanced Joining Technology Tianjin University Baosteel Research Institute Baoshan Iron & Steel Co. Ltd School of Mechanical Materials and Mechatronic EngineeringUniversity of Wollongong

The effects of Ni content and heat-treatment process on the toughness of a super ferritic stainless steel with 26 wt% Cr and 3.5 wt% Mo were investigated. It was found that with the increase of Ni content, the Charpy impact toughness improved remarkably, and transformed from cleavage brittle fracture to the most ductile fracture. There were no obvious differences between the high- and low-Ni contents on the microstructure and mechanical properties since the addition of Ni did not influence crystal structure, phase composition, and precipitation of ultra pure ferritic stainless steels. Meanwhile, the heat-treatment process was a key point to maintain a high level of toughness by optimizing structure and removing detrimental precipitation, i.e., chi phase.

关键词： Super ferritic stainless steel Nickel Heat treatment Toughness

Effects of cold metal transfer mode on the reaction layer of wire and arc additive-manufactured Ti-6Al-4V/Al-6.25Cu dissimilar alloys

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Journal of Materials Science & Technology 2021年第15期74卷 35-45页

作者： Yinbao Tian junqi shen shengsun Hu Jian Gou Yan Cui Tianjin Key Laboratory of Advanced Joining Technology Tianjin UniversityTianjin 300354China School of Materials Science and Engineering Tianjin UniversityTianjin 300354China Department of Mechanical Engineering University of MichiganAnn ArborMI 48109USA

Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer(CMT)*** current CMT(DC-CMT)mode was used for Ti alloy deposition,and DC-CMT or CMT plus pulse(CMT+P)mode was used for the Al alloy *** deposition of the first Al alloy layer,little and a significant amount of Ti alloy were melted using DC-CMT and CMT+P mode,***_(3)formed in the reaction layer when DC-CMT mode was used,while TiAl_(3),TiAl,and Ti3Al formed in the reaction layer when CMT+P mode was *** to using DC-CMT mode,more cracks occurred when using CMT+*** nanohardness of the reaction layer was between that of the Al and Ti alloys,irrespective of the CMT *** average tensile strengths of the samples using DC-CMT and CMT+P mode were 108 MPa and 24 MPa,***-CMT mode was more suitable for the wire and arc additive manufacturing of Ti/Al dissimilar alloys.

关键词： Ti/Al dissimilar alloys Wire and arc additive manufacturing Reaction layer Microstructure Mechanical properties

DETECTION METHOD OF SPOT WELDING BASED ON MULTI-INFORMATION FUSION AND FRACTAL

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Chinese Journal of Mechanical Engineering 2008年第6期21卷 76-81页

作者： LIU Pengfei SHAN Ping LUO Zhen shen junqi QIN Hede Luoyang Ship Material Research Institute Luoyang 471039 China School of Material Science and Engineering Tianjin University Tianjin 300072 China School of Xinxiang Etectromechanical Engineering Xinxiang 453000 China

A novel detection method of support vector machine （SVM） based on fractal dimension of signals is presented. And models of SVM are made based on nugget size defects of spot welding. Classification using these trained SVM models is done to signals of spot welding. It is shown from effect of different SVM models that these models with different inputs. In detection of defects, these models with inputs including sound signal have a high percentage of accuracy, the detection accuracy of these models with inputs including voltage signal will reduce. So the SVM models based on fractal dimensions of sound are some optimal nondestructive detection ones. At last a comparison between SVM detection model and ANNS detection model is researched which indicates that SVM is a more effective measure than Artificial neural networks in detection of nugget size defects during spot welding.

关键词： Multi-information fusion Support vector machine Box counting dimension Detection Spot welding

Effects of Cr Content on the Microstructure and Properties of 26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni Super Ferritic Stainless Steels

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Journal of Materials Science & Technology 2016年第6期32卷 552-560页

作者： Li Ma shengsun Hu junqi shen Jian Han Zhixiong Zhu Tianjin Key Laboratory of Advanced Joining Technology School of Materials Science and EngineeringTianjin University Baosteel Research Institute Baoshan Iron & Steel Co.Ltd. School of Mechanical Materials & Mechatronic EngineeringUniversity of Wollongong

By using scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, strength and hardness measurements, the microstructure, precipitation, mechanical properties, and corrosion resis- tance have been investigated for two super ferritic stainless steels, ***-2Ni and 29Cr-3.5Mo- 2Ni, with the aim to consider the effect of Cr content. The results showed that with the addition of Cr content, the recrystallization temperature was increased; the precipitation of Laves and Sigma （o） phases was promoted and the mechanical properties of super ferritic stainless steel were modified. Further- more, the pitting corrosion resistance and corrosion resistance to H2SO4 of the two super ferritic stainless steels were improved. In addition, suitable annealing processing is a key factor to maintain integrated performance by optimizing microstructure and removing detrimental precipitation phases.

关键词： Super ferritic stainless stee Heat treatment Microstructures Mechanical properties Corrosion resistance

Activating Flux Design for Laser Weldingof Ferritic Stainless Steel

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Transactions of Tianjin University 2014年第6期20卷 429-434页

作者： Ma Li School of Materials Science and Engineering Tianjin UniversityTianjin 300072China Tianjin Key Laboratory of Advanced Joining Technology Tianjin 300072China Research Institute Baoshan Iron & Steel Co.Ltd.Shanghai 200431China

The behaviors of YAG laser welding process of ferritic stainless steel with activating fluxes were investigatedin this study. Some conventional oxides, halides and carbonates were applied in laser welding. The resultsshowed that the effect of oxides on the penetration depth was more remarkable. Most activating fluxes improved thepenetration more effectively at low power than that at high power. The uniform design was adopted to arrange theformula of multicomponent activating fluxes, showing that the optimal formula can make the penetration depth up to2.23 times as large as that without flux, including 50% ZrO2, 12.09% CaCO3, 10.43% CaO and 27.48% MgO. Throughthe high-speed photographs of welding process, CaF2 can minimize the plasma volume but slightly improve the penetrationcapability.

关键词： ferritic stainless steel laser welding activating flux

Microstructure, Mechanical Property and Corrosion Resistance Property of Cr26Mo3.5 Super Ferritic Stainless Joints by P-TIG and Laser Welding

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Transactions of Tianjin University 2016年第5期22卷 451-457页

作者： Hu shengsun Pang Jie shen junqi Wu Wenyong Liu Lala Tianjin Key Laboratory of Advanced Joining Technology Tianjin University School of Materials Science and Engineering Tianjin University

The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results indicate that the widths of the center equiaxed grain zone(EGZ)and the columnar grain zone(CGZ)increase with the increase of heat input in both welding processes. The precipitates of Nb and Ti carbides and nitrides are formed in the weld metal(WM)and the heat affected zone(HAZ). The joints by laser welding show better tensile and corrosion resistance properties than those by P-TIG welding due to the heat concentration and lower heat input. The tensile strength and elongation increase with the decrease of heat input, and the fracture mode of the joints turns into ductile-brittle mixed fracture from ductile fracture when the welding method turns into P-TIG welding from laser welding. Moreover, the corrosion resistance of all joints declines slightly with the increase of heat input. Hence, laser welding is more suitable for welding Cr26Mo3.5 super stainless steel in engineering applications.

关键词： P-TIG welding laser welding super ferritic stainless steel microstructure mechanical property corrosion resistance property

紫铜与316L不锈钢脉冲激光焊微观组织及力学性能

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中国激光 2014年第7期41卷 93-98页

作者：李扬胡绳荪申俊琦天津大学天津市现代连接技术重点实验室天津300072 天津大学材料科学与工程学院天津300072

采用脉冲Nd:YAG激光对紫铜和316L不锈钢进行焊接,对不同搭接方式下的紫铜/不锈钢搭接接头的组织及界面进行研究分析,从而找到适合紫铜/不锈钢的搭接接头形式,并对其力学性能进行分析。实验中采用光学显微镜和能谱分析仪(EDS)对搭接界面... 详细信息

采用脉冲Nd:YAG激光对紫铜和316L不锈钢进行焊接,对不同搭接方式下的紫铜/不锈钢搭接接头的组织及界面进行研究分析,从而找到适合紫铜/不锈钢的搭接接头形式,并对其力学性能进行分析。实验中采用光学显微镜和能谱分析仪(EDS)对搭接界面进行观察。采用X射线衍射(XRD)对界面进行物相分析。采用扫描电镜(SEM)对端口形貌进行观察。采用维氏显微硬度机和拉伸试验机对焊接接头的机械性能进行测试。实验结果表明,因为铜和铁无限固溶所以紫铜与不锈钢焊接过程中没有金属间化合物生成,并且焊接接头采用紫铜在上,不锈钢在下的搭接方式能够获得良好的微观组织及力学性能。

关键词：激光技术脉冲激光焊微观形貌力学性能紫铜不锈钢

丝材+电弧增材制造钛/铝异种金属反应层的研究

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金属学报 2019年第11期55卷 1407-1416页

作者：田银宝申俊琦胡绳荪勾健天津大学材料科学与工程学院天津市现代连接技术重点实验室

分别利用直流冷金属过渡(CMT)和变极性CMT脉冲复合技术进行TC4和ER2319焊丝的堆积,实现钛/铝异种金属丝材+电弧增材制造,通过高速摄像及电信号采集系统进行电弧形态、熔滴过渡以及电流/电压信号的采集分析;利用OM、SEM、TEM、EDS、硬度... 详细信息

分别利用直流冷金属过渡(CMT)和变极性CMT脉冲复合技术进行TC4和ER2319焊丝的堆积,实现钛/铝异种金属丝材+电弧增材制造,通过高速摄像及电信号采集系统进行电弧形态、熔滴过渡以及电流/电压信号的采集分析;利用OM、SEM、TEM、EDS、硬度实验以及拉伸实验等方法对钛/铝异种金属构件的微观组织与力学性能进行分析。结果表明,变极性CMT脉冲复合堆积铝合金过程包括正极性脉冲阶段和负极性CMT阶段。在正极性脉冲阶段,电弧集中且热输入较大;在变极性CMT阶段,热输入较小且对构件具有明显的冷却效果。钛/铝异种金属构件的反应层包括过渡层和界面层,Ti Al3界面层的厚度约为10μm。在界面层存在微裂纹;反应层的硬度介于钛合金和铝合金之间;钛/铝异种金属构件的平均抗拉强度为65 MPa,所有拉伸试样均在界面层断裂,断裂方式均具有脆性断裂的特征。

关键词：钛合金铝合金变极性冷金属过渡脉冲复合增材制造