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Chen C.,Tianjin University | Chen C.,Tianjin Key Laboratory of Advanced Joining Technology | Hu S.,Tianjin University | Hu S.,Tianjin Key Laboratory of Advanced Joining Technology | And 3 more authors.
Robotics and Computer-Integrated Manufacturing | Year: 2013

In actual manufacturing process, many weldments have large dimensions and complex shapes, and they are usually assembled through a multi-pass welding process. The joints of the tube-sphere intersection (J-groove joints) are complex. This paper presents a complete solution in determining the welding paths based on a developed J-groove joint robot. Generating complex welding paths in terms of cubic B-spline curves is made easy using path control modules such as interpolation module and local modification module. The point inversion module using particle swarm optimization is introduced to address the partition of path, which is required of the welding process. Experimental results show that higher efficiency as well as better weld quality can be achieved, indicating a promising and practical use of the robot for welding applications, which is rarely available at present. © 2012 Elsevier Ltd. All rights reserved.


Cui C.,Tianjin University | Cui C.,Tianjin Key Laboratory of Advanced Joining Technology | Ye F.,Tianjin University | Ye F.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Surface and Coatings Technology | Year: 2012

Fe-based alloy coatings were deposited onto Fe360A (ISO 630) substrates by the High Velocity Oxy-Fuel (HVOF) technique. A Nd:YAG laser was used to remelt surfaces of the coatings. The experimental parameters were determined using an orthogonal experimental design approach. The microstructure and microhardness were studied using a metallographic microscope and a microhardness tester. The phase compositions were investigated by X-Ray Diffractomer (XRD). The effect of laser surface remelting on the corrosion resistance of Fe-based alloy coatings was evaluated by electrochemistry methods using a 10wt.% NaOH solution. It was found that there were four types of typical shapes of laser surface remelting pools. Large holes inside the coatings could be avoided when the remelted thickness was equal to or greater than the thickness of as-sprayed coatings. The microstructure of the laser surface remelted coatings was homogeneous, and its microhardness was promoted from an average of 600 HV 0.1 to 900 HV 0.1 because of emergence of the high hardness compounds such as SiO 2 and Fe 3Si after laser surface treatment. The remelted thickness was found to have a linear relationship with the laser power density, while the microhardness of laser surface remelted coatings exhibited a parabolic relationship. Analysis of the polarization curves showed that the free corrosion current density of laser surface remelted coatings could be lowered down from 25.63μA/cm 2 to 12.99μA/cm 2. Results of the electrochemical impedance spectroscopy (EIS) also indicated that laser surface remelting could improve the corrosion resistance of Fe-based alloy coatings. © 2011 Elsevier B.V.


Li H.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin Key Laboratory of Advanced Joining Technology | Han Y.,Tianjin Key Laboratory of Advanced Joining Technology | Xu Y.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2013

Effect of Cu-doping on the microstructure and transport properties of p-type thermoelectric BiSbTe alloy is studied. Quaternary Cu-Bi-Sb-Te alloys with general formula of CuxBi0.5-xSb1.5Te 3(x = 0, 0.04, 0.07, 0.1) are prepared by mechanical alloying and spark plasma sintering. The results show that the doping of copper has significant effect on the microstructure of the samples. With x increasing up to 0.07, the alloys begin to present an especial microstructure which consists of fault structure and dispersed pores. The electrical conductivities of the specimens are obviously improved to 1.9 × 105 S m-1 which is about 35% higher than the maximum value observed in pure Bi0.5Sb 1.5Te3 alloy by far. The maximum power factor value of 1.9 × 10-3 Wm-1 K-2 is obtained for the Cu0.1Bi0.4Sb1.5Te3 alloy between 325 and 450 K, being approximately twice as large as those of ternary Bi 0.5Sb1.5Te3 alloy obtained in our work around the temperature at which the maximum power factor is achieved. Nano-scale dispersed pores in Cu0.07-Bi0.43Sb1.5Te 3 and Cu0.1Bi0.4Sb1.5Te3 alloy have significant effect on the reduction of lattice thermal conductivity. ZT of 1.39 can be obtained for Bi0.5Sb1.5Te3 alloy at 390 K. © 2013 Elsevier B.V. All rights reserved.


Zhao L.,Tianjin University | Zhao L.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin University | Jing H.,Tianjin Key Laboratory of Advanced Joining Technology | And 6 more authors.
Materials and Design | Year: 2012

The present study mainly investigated Type IV cracking occurring in the fine grained heat affected zone (FGHAZ) in the welded joint of ASME P92 steel at high temperature and low applied stress by numerical simulation method. Based on the modified Karchanov-Rabotnov constitutive equation, the user defined material subroutine (UMAT) was complied and the creep damage accumulation was carried out by finite element method using ABAQUS codes for the welded joint at 650 °C and 70. MPa. Calculated results revealed that the most severe creep damage and the highest equivalent creep strain occurred in the FGHAZ because of high maximum principle stress and high maximum principle stress. Furthermore, the effect of groove angle and HAZ width on the creep damage accumulation was investigated. It indicated that a small groove angle and a narrow FGHAZ width could deteriorate the creep damage accumulation because of the degradation of maximum principle stress and stress triaxiality in the FGHAZ. © 2011 Elsevier Ltd.


Zhao L.,Tianjin University | Zhao L.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin University | Xu L.,Tianjin University | And 2 more authors.
Engineering Fracture Mechanics | Year: 2012

Effects of constraint induced by crack depth on creep crack behavior of P92 steel was investigated by experimental investigation and numerical simulation. Creep crack growth tests were carried out on compact tension specimens with different crack depths. It revealed that the high constraint affected creep crack initiation time and steady creep crack growth rate. Then, the crack-opening stress distribution at crack tip during creep crack growth process was obtained by finite element method (FEM) analysis. The corresponding variation of constraint parameter Q was also obtained. Finally, a C--Q approach was employed to characterize the creep crack growth rate. © 2012 Elsevier Ltd.


Xu L.Y.,Tianjin University | Xu L.Y.,Tianjin Key Laboratory of Advanced Joining Technology | Yang G.Y.,Tianjin University | Yang G.Y.,Tianjin Key Laboratory of Advanced Joining Technology | And 5 more authors.
Nanotechnology | Year: 2014

With the aim of preparing a method for the writing of electronics on paper by the use of common commercial rollerball pens loaded with conductive ink, hybrid conductive ink composed of Ag nanoparticles (15 wt%) and graphene-Ag composite nanosheets (0.15 wt%) formed by depositing Ag nanoparticles (∼10 nm) onto graphene sheets was prepared for the first time. Owing to the electrical pathway effect of graphene and the decreased contact resistance of graphene junctions by depositing Ag nanoparticles (NPs) onto graphene sheets, the concentration of Ag NPs was significantly reduced while maintaining high conductivity at a curing temperature of 100 ° C. A typical resistivity value measured was 1.9 × 10-7 Ω m, which is 12 times the value for bulk silver. Even over thousands of bending cycles or rolling, the resistance values of writing tracks only increase slightly. The stability and flexibility of the writing circuits are good, demonstrating the promising future of this hybrid ink and direct writing method. © 2014 IOP Publishing Ltd.


Ding J.-K.,Tianjin University | Ding J.-K.,Tianjin Key Laboratory of Advanced Joining Technology | Wang D.-P.,Tianjin University | Wang D.-P.,Tianjin Key Laboratory of Advanced Joining Technology | And 4 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2014

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas (VPTIG) welding process and the effects of post weld heat treatment (PWHT) on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded (AW) sample and PWHT sample. The PWHT method used on the samples was solution treatment (535 °C, 30 min), water quenching and artificial aging (175 °C, 12 h). The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively. © 2014 The Nonferrous Metals Society of China.


Liu Y.,Tianjin University | Liu Y.,Tianjin Key Laboratory of Advanced Joining Technology | Wang L.,Tianjin University | Wang L.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Journal of Materials Processing Technology | Year: 2011

Ultrasonic surface rolling (USRP) is a newly developed process in which ultrasonic vibration and static force are applied on work-piece surface through the USRP operator to generate a nanostructured surface layer with mechanical behaviors highly improved. Compared with other surface severe plastic deformation (S2PD) methods, it can realize mechanized machining and be directly used for preparing final product. Notwithstanding the excellent performance of USRP, elaborate relation between process parameters and surface layer characteristics is still inadequacy due to inconvenient and costly experimental evaluation. Therefore, in this paper a three-dimensional finite element model (FEM) has been developed to predict the treatment conditions that lead to surface nanocrystallization. Simulated results of surface deformation, stress and strain are investigated to assess the formation of nanostructured layer. The numerical results from the FEM corresponds well with the values measured experimentally, indicating that this dynamic explicit FEM is a useful tool to predict the processing effects and to relate the treating parameters with the surface layer in terms of the size of nanostructured layer, residual stress and work hardening. © 2011 Published by Elsevier B.V. All rights reserved.


Han Y.D.,Tianjin University | Han Y.D.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.Y.,Tianjin University | Jing H.Y.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Materials Chemistry and Physics | Year: 2012

In this study, the effect of microstructure at the base metal (BM), the fine grain heat affected zone (FGHAZ), the coarse grain HAZ (CGHAZ) and weld metal (WM) under different welding heat input on hydrogen permeation in X80 steel weldments have been investigated. Base metal showed the highest effective diffusivity. With each heat input, the effective hydrogen diffusivity in FGHAZ is comparable to that of the base metal. The effective hydrogen diffusivity in weld metal was lower than that in CGHAZ. With increasing the welding heat input, the effective diffusivity in different zones of the weldment decreased correspondingly. Non-metallic inclusions were not detected in each specimen. Constituents in microstructure under low heat input are likely to agglomerate during accelerated cooling. The retained hydrogen may create an unpredictable susceptibility to hydrogen cracking at the CGHAZ even existing during service. © 2011 Elsevier B.V.


Zhao L.,Tianjin University | Zhao L.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin University | Jing H.,Tianjin Key Laboratory of Advanced Joining Technology | And 6 more authors.
Materials and Design | Year: 2014

In order to clarify the effect of constraint induced by specimen size on creep crack growth behavior of P92 steel welded joint, creep crack tests were carried out on the compact tension specimens with thick thickness and thin thickness, the crack tip of which were located at different distinct zones of welded joint. Tested results revealed that even in thin thickness specimens, fine grained heat affected zone specimens exhibited a fast creep crack growth rate compared with other micro-zones specimens due to a low creep crack resistance and a high multistress state. The fractographies of these specimens exhibited an accelerated number of spherical particles that were caused by the coalescence of creep voids. Furthermore, the correlation of Cz.ast; with creep crack growth rate was dependent on specimen thickness. As the specimen thickness increased from 10 to 30mm, the creep crack growth rate increased. This was due to the increase in constraint level ahead of crack tip during creep crack propagation. © 2014 Elsevier Ltd.

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