Effect of welding sequences

Nomenclature q C T t fqg Q g hf TB TA ½N fTe g ½C ½K fFe g fP g ff g fug feg density specific heat temperature time heat flux the rate of internal heat generation unit outward normal vector film coefficient bulk temperature of the adjacent fluid temperature at the surface of the model element shape functions nodal temperature vector R q V C ½N T ½N dV R R T T RV ½B ½D½B dV R þ A hf ½N ½N dA Q½N dV þ A hf TB ½N dA V surface force vector body force vector displacement vector strain vector frg ½B ½L fRg fDre g fDep g fDe g fDp g fUe g fDT g fC th g fDTe g ½M mþ1 fK1 g mþ1 fK2 g rY rX r/ rr stress vector strain–displacement matrix differential operator matrix R R ½N T fP g dA þ V ½N T ff g dV A nodal stress increment matrix fDe g þ fDp g elastic stiffness matrix plastic stiffness matrix nodal displacement vector temperature increment matrix thermal stiffness matrix nodal temperature increment matrix temperature shape function R T ep RV ½BT fDth g½B dV ½B fC g½M dV V longitudinal residual stress transverse residual stress circumferential stress radial stresses
Abstract Accurately predicting welding residual stresses and developing an available welding sequence for a weld system are pertinent tasks since welding residual stress is inevitably produced in a welded structure. This study analyzes the thermomechanical behavior and evaluates the residual stresses with various types of welding sequence in single-pass, multi-pass butt-welded plates and circular patch welds. This is achieved by performing thermal elasto-plastic analysis using finite element techniques. Furthermore, this investigation provides an available welding sequence to enhance the fabrication process of welded structures. Ó 2003 Elsevier Science Ltd. All rights reserved.
a bห้องสมุดไป่ตู้
b,*
, Wen-Cheng Tseng
c
University of National Defense, Chung Cheng Institute of Technology, Ta-shi, Tao-Yuan 335, Taiwan, ROC Department of Mechanical Engineering, Da-Yeh University, 112 Shan-Jiau Road, Da-Tsuen, Changhua 515, Taiwan, ROC c 455 Wing Air Force, Taiwan, ROC Received 26 March 2002; accepted 2 November 2002
inner surface. Ueda et al. [7] investigated the effectiveness of the heat-sink welding to improve the residual stresses of a pipeÕs circumferential joint. Chou and Lin [8] reduced residual stresses by parallel heat welding type 304 stainless steel specimens. For the effect of welding sequence, Weck [9] and Watanabe et al. [10] have studied how welding sequence affect residual stress build-up. Kihara et al. [11,12] investigated how welding sequence affects residual stress and shrinkage in slit-type welds and circular-path welds. Jonassen et al. [1] describes the effects of certain block and other special welding procedures on the magnitude of residual stresses in buttwelded steel plates of 1-in. thickness. When welding a long butt-welded joint, multi-pass butt-welded joint or a path joint, various types of welding sequences are used in order to reduce residual stress and distortion. The selection of a proper welding sequence is an important practical problem. However, accurately predicting the residual stresses of welding sequences is extremely difficult because the thermal and mechanical behaviors in welding include a local high temperature, temperature dependence of material properties, and a moving heat source. Therefore, this investigation performs a thermal elasto-plastic analysis using finite element techniques to analyze the thermomechanical behaviour and evaluate the residual stresses with various types of welding sequence in single-pass, multipass butt-welded plates and circular patch welded plates. Furthermore, this study provides an available welding sequence to improve the fabrication process of welded structures.
0045-7949/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0045-7949(02)00447-9
274
T.-L. Teng et al. / Computers and Structures 81 (2003) 273–286
Keywords: Welding sequences; Residual stresses; Butt-welded; Circular patch welds
1. Introduction Metallurgical welding joints are extensively used in the fabrication industry, including ships, offshore structures, steel bridges and pressure vessels. Among the merits of such welded structures include a high joint efficiency, water and air tightness, and low fabrication cost. However, residual stresses and distortions can occur near the weld bead due to localized heating by the welding process and subsequent rapid cooling. High residual stresses in regions near the weld may promote brittle fractures, fatigue, or stress corrosion cracking. Meanwhile, residual stresses in the base plate may reduce the buckling strength of the structure members. Therefore, welding residual stresses must be minimized to control them according to the respective requirements. Previous investigators have developed several methods, including heat treatment, hammering, pre-