Date

2016

Document Type

Thesis

Degree

Master of Science

Department

Mechanical Engineering

First Adviser

Nied, Herman F.

Other advisers/committee members

Harlow, D G.

Abstract

Residual stresses are generated from the non-linear thermal loading and unloading cycles that occur during a typical multi-pass ARC welding process. Large residual stresses and plastic strains will in turn cause reliability problems closely associated with cracking and distortion in welded structures, which will ultimately reduce the structure’s fatigue life. In this study, the particular structure of interest is an outlet manifold fabricated with large circumferential welds. SYSWELD is used to simulate the welding process of the Cone and Tee weld in the outlet manifold using four numbers of weld passes (1 weld pass, 4 weld passes, 10 weld passes and 20 weld passes) and two different material groups (Group 1: Incoloy 800 HT for base alloy and Inconel 617 for filler metal, Group 2: 316L for both base alloy and filler metal), three different boundary conditions and two different plasticity model (Isotropic hardening and kinematic hardening). By using Finite Element Analysis and comparison analysis with varying singular welding process parameter, the influence of different numbers of weld passes, materials, boundary conditions and plasticity models on the residual stress distribution can be found. It is shown that the number of welded passes has significant influence on the residual stress distribution. The simulation results also indicate that the Inconel alloy group and the 316L materials will give rise to similar plastic deformation zones, but different stress value in the same positions. Additionally, the boundary conditions lead to localized residual stress concentrations in area near rigid clamped conditions. Isotropic and kinematic plasticity models result in slightly differences on stress values of plastic deformation areas and are also discussed in detail in this study.

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