Date

2015

Document Type

Thesis

Degree

Master of Science

Department

Mechanical Engineering

First Adviser

Nied, Herman F.

Abstract

The objective of this study is to predict the magnitude and spatial variation of the residual stresses in an autogenously welded flat plate. Autogenous welding is a fusion welding process using heat without the addition of filler metal to join two pieces of the same metal. The residual stresses in a flat plate, close to the weld pool, are closely examined in this study. Using the welding simulation program SYSWELD, a 2-D geometric model was constructed using ANSYS 15.0, then meshed with quadratic 2-D elements in Visual-Mesh 10.0. In this study, mesh refinement is critical, especially near the melt boundary, so that realistic results can be obtained where the thermal and material property gradients are most severe. In the welding simulations, material properties for 316L austenitic stainless steel and S355J2G3 carbon steel are chosen to contrast the difference in residual stresses obtained from two very different classes of steel. In addition, results are given for three different boundary conditions. It is shown that the material properties and boundary conditions have a significant influence on the residual stresses. Of particular interest is the comparison of the final residual stresses. It is shown that the phase change transformations during cooling in carbon steels from austenite to bainite and finally martensite, result in highly localized compressive residual stresses, significantly reducing the magnitude of the overall surface tensile stresses in the heat affected zone near the weld boundary.

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