ABSTRACT

In this study, the proposed linearized inherent strain method for predicting straightening of welded structures is investigated. Thermal elastic-plastic analysis is used to compute inherent strain of a thin flat plate caused by line heating. An accurate gas heat source model is employed in simulating the heating process. Transversal inherent strain is linearized from the computed distortion of the flat plate and applied in the elastic analysis, using higher order Gauss-Legendre (4-nodes shell elements). The accuracy of the proposed method is demonstrated by comparing the angular distortion of both analyses. Furthermore, different plate orientations are taken into account.

INTRODUCTION

Welding process is one of the most popular assembly method used by many industries such as ships and bridges. However, welding produces many unavoidable problems such as welding residual stress, crack propagation, and welding distortion especially for thin plates and large structures. The welding should be straightened, or the quality of the structure will decrease and the maintenance cost will increase. Welding distortion is caused due to shrinkage during the thermal cycle. It can be separated into the longitudinal shrinkage, transverse shrinkage, and angular distortion, see Fig. 1.

In the last decades, ship designers have improved ship performance using thinner and lighter steel plates to reduce the ship weight. However, several problems with welding distortion have appeared as a result of thin plates welding for large structure fabrication. Mechanical and thermal straightening techniques are used to solve this problem. But mechanical techniques are difficult to apply to 3-D structures as ship blocks. Therefore, thermal processes are preferred because it is more economical and more flexible. These techniques create irreversible strain (inherent strain). As discussed by Ueda (1991, 1993), heat straightening consists of applying specific controlled heat patterns to the plastically deformed regions of welded structures in a single or repetitive heating phase and in-plane contraction during the cooling phase. Unfortunately, this method depends most of the cases on the experience of the skilled workers.

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