Study Of Welding Deformation Of A Deck Grillage With Mechanical Constraints

Deck grillages are important parts of marine structures.Welding-induced deformation and residual stresses reduces the loading capability and assemble precision of the welded grillages.Welding deformation can be decreased by applying mechanical constraints during the welding process.Numerical method is a valid way to simulate the process in order to give instruction to practical building process.In this dissertation,welding simulation of a deck grillage was carried out by using thermal elastic plastic method and shell/solid model in ABAQUS.The calculation efficiency was improved by applying segmented moving heat source and static substructure technique.Influences of vertical constraints,clamped constraints and mixture constraints on the welding deformation and residual stresses of the deck grillage were studied.The main contents are as follows:(1)The comprehensive review on the current situation of prediction of welding deformation and residual stress of welded structure,building techniques of marine structures and studies of applying mechanical constraints during welding process.(2)Introducing basic theory of temperature field analysis,mechanics field analysis and the shell/solid model.Welding simulation of a deck grillage was carried out with thermal elastic plastic FEM and shell/solid model.Segments moving heat source and static substructure technique were also used.The distribution of welding deformation and residual stresses of the grillage was analyzed.(3)Welding simulation of the deck grillage under five different vertical constraints cases was conducted to study the influence of vertical constraints on welding deformation and residual stress.It is shown that the global deformation and the local panel distortion can be reduced greatly by applying vertical constraints.The welding deformation decreases as the area of constraints increases.The residual stress in the middle surface of the grillage is barely influenced by the constraints.(4)Welding simulation of the deck grillage under three different boundary clamped constraints cases was conducted to study the influence of vertical constraints on welding deformation and residual stress.It is shown that welding distortion of the free boundary can be reduced greatly by applying the constraints.The residual stress of the grillage is barely influenced by the constraints.(5)Combining vertical and boundary clamped constraints.The mixed constraints can significantly decrease shrinkage deformation,free boundary distortion,global and local deformation of the deck grillage.The mixed constraints case is selected as the relatively optimal constraints case.