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Distortion in welded steel plates


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Authors

Leggatt, Richard Howard 

Description

An experimental and theoretical investigation of transverse shrinkage and angular distortions caused by welding of steel plates is described. A review of previous research reveals few measurements or formulae that are directly comparable; even when comparisons can be made the results are widely scattered. The experimental work reported in this thesis include shrinkage measurements at over 160 weld beads. The distortion at submerged arc bead-on-plate welds on large unrestrained plates of Grade 43 weldable structural steel are taken as the basic case with which all other results are compared. The parameters investigated include weld conditions, weld process, plate dimensions and restraint. The effects of multipass welding, root gap, edge preparation, and tacking of butt welds have also been explored. A computer model of transverse distortion at single pass welds is described. The program follows the accumulation of distortion as the temperature distribution associated with the weld pool moves along the plate centre-line. Temperature calculation is based on previously published analytical solutions to the heat flow equation, but uses empirically adjusted values of the thermal properties which give improved temperature prediction. The high temperature zone near the path of the weld pool is split longitudinally and through the thickness into layertype elements which have non-linear, elasto-plastic, load history and temperature dependent material properties. The remainder of the plate is split into two dimensional elastic elements which model in-plane and out-of-plane distortions and stresses. A comparison was made of computed and experimental distortions at bead-on-plate welds. The theoretical results agreed with the principal conclusions of the experimental investigations. There were some areas of quantitative disagreement: these highlighted the critical importance of the shape of the fusion zone and the accompanying temperature distribution. The investigation has yielded new insights into the underlying mechanisms of weld distortion. These have led to simple formulae for transverse shrinkage and angular distortion at single and multipass welds, and for the reduction in angular distortion due to rotational restraint.

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Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge