United States Department of Transportation
i
Finite Element Modeling of Residual Stresses in Electroslag Butt Welds
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2000-03-01
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[PDF-10.46 MB]
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OCLC Number:43781303
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Edition:Final Report
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Abstract:Shop fabricated electroslag (ES) welds used in bridge construction have had a history of low toughness in the fusion and heat affected zones. In addition, conventional inspection of ES weldments under shop fabrication conditions fail to consistently detect and/or correctly size weld discontinuities. These problems have led to a Federal Highway Administration requirement for removal, re enforcement, or re-evaluation of the integrity of ES weldments in existing Federal bridges. The specific tasks of this study were: a) to develop an understanding of ES weld-induced residual stresses for A36 steel with an emphasis on assessment of bridge-specific weld parameters and residual stress measurement; and b) computational modeling of ES welding and the resultant stress distribution. The ES weldments assessed in this study were those used in the fabrication of the Oregon State I-205 West Linn Bridge. This research was performed by numerical modeling based on unknown welding operation parameters. Experimental assessment of fusion zone characteristics was used as input data for the computational modeling work. Selective etching techniques were used to reveal the solidification band formed at the fusion line interface during ESW. Analysis of these solidification bands allowed determination of weld pool profiles formed during welding, which are a direct function of the welding parameters. Two-dimensional (2D) and three-dimensional (3D) models were developed using FEA methods to simulate the ESW process and to analyze the effect of operating conditions on residual stress distribution. Both two-dimension (2D) and three-dimension (3D) thermal heat transfer ESW finite element analysis (FEA) models were developed using the Lagrangian system, only 3D thermal models were developed using the Eulerian coordinate systems. Experimental assessment of bridge-specific residual stress fields was attempted. Coring and subsequent sectioning techniques were used to measure residual stresses associated with the ES weldments. However, the presence of continuous fusion line weld repairs perturbated the underlying ESW residual stress field. Thus, even though the results tend to support the 3D FEA residuals stress analysis, the experimental results can not be used to validate or invalidate the computational results. Surface residual stress assessment by the blind hole drilling method was unsuccessful.
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