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The Influence of Welding Residual Stress and Deformation on Plastic Deformation Behavior of Tube Hydroforming

Author: HuangZuo
Tutor: FangHongYuan
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: tailor-welded tube hydroforming residual stress angular distortion finite element simulation
CLC: TG404
Type: Master's thesis
Year: 2012
Downloads: 32
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Abstract


Tailor-welded tube has been widely used in the field of hydroforming technique,for such advantages as maintaining the structural integrity, optimizing distributionof materials, reducing weight and improving quality. However, current studies onhydroforming of tailor-welded tube are mainly focusing on distribution of wallthickness after forming process, regular pattern of welding line and applications oftailor-welded tube. There is no systematic analysis on the influence of residual stressand deformation around the welding line, which is critical to tailor-welded tubehydroforming process. These factors impede the development of hydroformingpossesses of tailor-welded tube seriously.Welding residual stress, deformation and angular distortion were firstly studiedby finite element simulation, the hydroforming processes of normal andtailor-welded tube were simulated relatively. Then, the influence of each factor wasgiven to conduct tailor-welded hydroforming theoretically.Using304stainless steel plate to measure actual temperature contrasting withthe simulation results, accurate convection heat transfer coefficients of stainlesssteel and air were determined, my which the veracity of simulation can be ensured.Mechanical properties of the heat affected zone (HAZ) were obtained by thermalsimulation method. Mechanical properties of the welding line were studies usingplate welding and tensile test. All these experiemental resules can make sure that thefinite element simulation can be conducted successfully.Finite element code Marc was used to model the normal hydroforming process,evolutions of stress and strain were studied at the preliminary forming, paster andunloading stage. The largest plastic deformation, which increased and shift tocentral plane of symmetry with the tube bulging, was located at the junctionbetween bulging and transition region at the preliminary forming stage. Moreover,circumferential tensile stress was the largest at the expanded zone and increaseduntil the end of preliminary forming stage. The circumferential plastic deformationwas a constant, the feed along the axis compensated the circumferential tensile,which transformed to compressive stress finally. The stress on the tube was nearly at0when the unloading stage finished.Influence of welding angular distortion and residual stress on tailor-weldedtube hydroforming were studied during the numerical simulation process. Thebending moment caused by the welding angular distortion could be eliminatedentirely, because the region of angular distortion is too small to create enoughbending moment. So the welding line transformed to concave after bulging. The major welding residual tensile stress at the weld toe integrated with the bulgingtensile stress generated the biggest circumferential tensile stress at the weld toe,which is the vulnerable zone during the tailor-welded tube hydroforming.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Stress and deformation of welded structures
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