Abstract
Residual stresses change the stress ratio of fluctuating stresses, hence seriously affect the fatigue life of orthotropic steel decks (OSDs) under traffic loading. Residual stress distributions near the U rib-diaphragm joints are very complicated and need to be investigated further. In this paper, a systematic method has been proposed for calculating the residual stress field in the joint of U rib and diaphragm due to thermal cutting and welding. Firstly, a mathematical model of cutting heat sources was established to predict the temperature field. Then, a numerical elastoplastic thermomechanical model was built to predict the residual stress evolutions in a diaphragm-rib joint through the whole fabrication process involving flame cutting and welding. Moreover, the simulated temperature contours at the fusion zone and the residual stress distributions in the rib-diaphragm joint were compared and verified against the experimental ones. The numerical results showed a great agreement with the experimental ones, indicating that the heat source model can be used to accurately predict the temperature field during flame cutting. Finally, the validated numerical model was utilized to conduct parametrical analyses on the effects of thermal processing rates, e.g., the cutting and welding speeds and on the residual stress distribution in the rib-diaphragm joint. The results indicate that a faster cutting speed and a slower welding speed can decrease the residual stress magnitude at the rib-diaphragm joints and reduce the high-stress zone near the diaphragm cutouts.
Highlights
Orthotropic steel decks (OSDs) are widely used in long-span bridges because of their superior features, such as overall light self-weight, fast construction, high loading capacity, etc. [1,2]
Rib-diaphragm joints in OSDs, the distribution of residual stress was analyzed through a two-step thermo-mechanical analyses using the finite element (FE) method: (1) a rectangular steel plate was cut into the Materials 2020, 13, x FOR PEER REVIEW
heat-affected zone (HAZ) widens under the effect of the welding heat sources, causing the welding residual stress curves to move toward the center of the diaphragm
Summary
Orthotropic steel decks (OSDs) are widely used in long-span bridges because of their superior features, such as overall light self-weight, fast construction, high loading capacity, etc. [1,2]. The manufacture of U rib-diaphragm joints includes many processes and the residual stress distribution can be caused by welding, and by flame cutting. Previous studies showed that the joints between the diaphragms and U ribs of steel box girders suffer compressed stress under the static load of vehicles [23], which are theoretically unlikely to generate cracks This problem of fatigue has increasingly become one that plagues scholars around the world. The evolution of residual stresses considering the continuous process of flame cutting and fillet welding should be investigated to understand fatigue mechanisms of rib-diaphragm joints in OSDs. In the present study, a thermo-mechanical method has been proposed to predict the residual stress distribution in the joint between U rib and diaphragm during the thermal cutting and welding process.
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