Numerical Analysis of Welding Residual Stress Relaxation in High-Strength Multilayer Weldment Under Fatigue Loads
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INTRODUCTION
WELDING residual stress is caused by irregular temperature distribution during welding. Welding residual stress has a great impact on fatigue strength and on the fatigue life of welded structures, and the effects vary by whether the residual stress is tensile or compressive.[1] Tensile residual stress is known to deteriorate the fatigue life of welded structures and cause stress corrosion cracking. For this reason, the residual stress in the weldments after welding of transportation equipment, ships, offshore plants, and steel bridge structures that receive continuous fatigue load is removed by using various methods. The methods for relaxing welding residual stress include postweld heat treatment, mechanical load application, vibration of the weldment, and peening or hammering of the parts with tensile residual stress to cause compressive residual stress on the surface.[2,3] Among these methods, the mechanical stress relaxation (MSR) method applies an external load to the mechanical component with residual stress and makes the sum of the applied stress and the residual stress reach the yield stress of the material so that the residual stress will be relieved or redistributed. The welding residual stress is gradually relieved even under fatigue or vibration load as well as under a static load, and the relaxation level of the residual stress is known to be determined by the size and number of repeated loads.[4–6] When assessing the fatigue life of welded structures, the effects of residual stress that affect the fatigue life of
HUI-JUN YI is with Hyundai-Rotem Company, Chang-won 51413, Korea. Contact e-mail: [email protected] YONG-JUN LEE is with the The 2nd Land System Team, Defense Agency for Technology and Quality, Changwon 51461, Korea. Manuscript submitted August 13, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
the structure must be considered. Especially for the design of steel bridge structures, the repeated load and vibration during use must be evaluated and their effect on the fatigue life must be predicted in the design. Morrow et al. and Iida et al. studied the relaxation of welding residual stress and stress relaxation mechanisms under repeated load by experimental methods. They researched the effects of the number of repeated loads and the size of the external load on 700-MPa grade carbon steels.[7–9] Nevertheless, they used experimental methods with fatigue specimens and did not consider residual stress relief problems. Accordingly, in this study, a finite element analysis model for prediction of the welding residual stress for multipass weldments of 1100-MPa high-strength steel and for prediction of the mechanical stress relaxation after external repeated loads was presented and verified through an experimental method. For this purpose, residual stress generated during the welding process was predicted through thermal–mechanical coupling analysis followed by mechanical analysis of residual stress relaxation by repeated loads.
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EXPERIMENTAL PROCEDURES
For this test, mechanical stress
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