Implications of three-dimensional numerical simulations of welding of large structures

Common and important problems associated with the welding of large structures are induced distortion and residual stresses, both dif f icult to simulate accurately given the intensive computational demands of such severely nonlinear processes. Current simulations usually either involve small and simple structures such as butt-jointed plates, or emphasize the local weld zones, ignoring the surrounding structure. Such simulations, though not demanding computationally, de-emphasize effects of interactions between the weld zone and the remaining welded structure. The coupl ing between a local weld zone and a surrounding structure, however, can have a significant effect on the final state of distortion and residual stresses. This coupling derives from several sources, some of which are complex and nonintuit ive. A surrounding structure influences a weld both through the elastic constraint offered by the structure and through the distortion of the structure due to thermal expansion. Additionally, newly deposited weld material couples previously separated parts, thereby changing the nature of the structure as the welding electrode advances. Motion of opposing sides of a weld root opening due to structural asymmetry also complicates a simulation. This paper examines structure/weld interaction issues during welding processes through twoand three-dimensional simulations of a ring-stiffened cylinder. Such a structure consists of a circular cyl inder and a ring, wh ich accentuate the effects of structure/weld interactions because of the high ratio of radius to cross-sectional dimension. Compromises and limitations involved in two-dimensional simulations are also discussed. Specific issues of weld root opening and fixturing are considered. 5. B. BROWN is with the Massachusetts Institute of Technology, Cambridge, Mass. H. SONG is with Anadrill Schlumberger, Sugarland, Texas. Introduction Distortion and residual stresses resulting from welding represent significant problems in the accurate fabrication of large structures. Although the capability to predict these phenomena would provide substantial assistance to the design and fabrication of welded structures, both welding distortion and induced stresses are diff icult to simulate accurately given the intensive computational demands of such severely nonlinear processes. As a result, current simulations usually either involve small and simple structures such as butt-jointed plates, or emphasize the heat-affected zones, ignoring the surrounding structure. Such simulations remain computationally demanding, yet still de-emphasize effects of interactions between the local weld zone and the remaining welded structure. Finite element simulation of the welding process has been remarkably successful in predicting certain features of welding, particularly temperature distribut ion, and to a lesser extent, stress, strain and displacement fields. Many of the papers published in the literature use two-dimensional models, focusing attention only to the local zone around the weld pool. A few researchers have per-