The Influence of Mechanical Constraint on the Welding Deformation of a Large-scale Ship Bottom Grillage

Li, Gongrong (State Key Laboratory of Ocean Engineering) | Chen, Zhen (Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE)) | Luo, Yu (Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE))

OnePetro 

Abstract

Based on thermal elasto-plastic finite element method (FEM), the welding simulation of a large-scale ship bottom grillage was carried out in this paper. The structure comprises five transverse floors and three longitudinal girders. In order to enhance modeling and calculation efficiency, shell elements with section integration are adopted to model the entire structure and solid elements to model the local details of weld line region. Linear constraint equations are established between degrees of freedom of shell and solid elements. The techniques of segmented moving heat source model and static substructure are adopted in order to reduce the computation time of models. Some key welding parameters such as heat input, welding speed and welding sequence are considered in the analysis. The welding deformations under two different constraints, including global bending, transverse angular distortion and torsion distortion, are analyzed and compared in this paper.

Introduction

Welding is a principal jointing method in the construction of ship and offshore structures. It offers several advantages over mechanical jointing methods such as structure integrity, flexibility of design, weight reduction and cost saving etc. (Deng et al., 2007). However, it is inevitable that distortions and stresses are induced during welding due to the non-uniform expansion and shrinkage of material near weld lines (Jang et al., 2002). Welding deformation has negative effects on the accuracy of assembly, external appearance, and strengths of welded structures. In many cases, additional costs and schedule delays are incurred from straightening welding deformation. On the other hand, the design of engineering components and structures relies on the achievement of small tolerance (Deng et al., 2008a). Therefore, understanding and controlling the formation of welding induced deformation are of importance at the design stage of ship and offshore structures.

During the past several decades, thermal elasto-plastic finite element method (FEM) has been proven to be an effective tool for the prediction of welding residual stresses and distortions. Deng & Murakawa (2008a) used the thermo-elastic–plastic FEM to predict welding distortion and residual stress in a thin plate butt-welded joint and the accuracy were verified by experimental results. J. Sun et al. (2014) adopted a developed elasto-plastic FEM to simulate the welding temperature field, residual stress distributions and deformations induced by LBW and CO2 gas arc welding in low carbon steel thin-plate joint. The numerical results agreed well with the experimental results. G. Fu et al. (2014) investigated the welding residual stress and distortion in T-joint welds under various mechanical boundary conditions. FEM analysis and experimental results showed that transverse residual stress, out-of-plane displacement, angular distortion and transverse shrinkage depended on the mechanical boundary conditions significantly. A.A. Bhatti et al. (2015) studied the influence of material properties on welding residual stresses and angular distortion in T-fillet joints based on FEM. The numerical predictions of angular distortion and transverse residual stresses were validated with experimental measurements. However, thermal elasto-plastic FEM is time-intensive and is limited to simulation of small-scale structures such as fillet and butt joints, as mentioned above.