Abstract
Residual stresses are a consequence of welding in various structures such as ships and offshore structures. Residual stresses can be relaxed or redistributed according to the load levels during operation. The elastic shakedown phenomenon can be considered as one of the reasons for this change. This paper studies the relaxation/redistribution of weld residual stress during different levels of shakedown in a butt-welded plate chosen according to ship design and welding procedures. Welding was performed on DH36, a ship structural steel. Neutron diffraction was used to measure residual stresses in these plates in the as-welded state and after different levels of shakedown. A mixed hardening model in line with the Chaboche model is determined for both weld and base material. A numerical model is developed to estimate the shakedown limit on butt-welded plate. Further, the redistribution of residual stress in a numerical weld model according to the different levels of shakedown limit is studied. Based on the shakedown limit of the butt-welded plate, a shakedown region is determined, where the structure will undergo elastic shakedown in the presence of an existing residual stress field if the maximum stress on the load section after a few initial cycles is in the shakedown region.
Highlights
Welding is the primary joining technique used in many offshore structures which results induces in complex residual stresses in many components
Elastic shakedown is defined as a plastic deformation causing a change in plasticity induced residual stress during the first few load cycles, followed by an elastic response which is associated with a limit called the shakedown limit [2]
The Finite Element (FE) model is subjected to increasing loads starting from 50% of yield strength of the parent material
Summary
Welding is the primary joining technique used in many offshore structures which results induces in complex residual stresses in many components. Elastic shakedown is defined as a plastic deformation causing a change in plasticity induced residual stress during the first few load cycles, followed by an elastic response which is associated with a limit called the shakedown limit [2]. A primary load above the shakedown limit will result in reverse plasticity or ratchetting [3]. For a rigid–perfectly-plastic solid the load limit can be determined by using Melan’s lower bound and Koiter’s upper bound theorems [4,5]. These theorems in their original form assume linear kinematics and elastic-perfectly plastic material. It is recommended to adopt analysis with mixed hardening models such as Chaboche [6, 7]
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