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Title of Thesis

Analysis Of Residual Stresses And Distortions In Circumferentially Welded Thin-Walled Cylinders

Author(s)

MUHAMMAD EJAZ QURESHI

Institute/University/Department Details
Department of Mechanical Engineering, College of Electrical and Mechanical Engineering / National University of Sciences and Technology (NUST), Rawalpindi
Session
2008
Subject
Mechanical Engineering
Number of Pages
256
Keywords (Extracted from title, table of contents and abstract of thesis)
Analysis, Residual, Stresses, Distortions, Circumferentially, Welded, Thin-Walled, Cylinders,  Slavianov, thermal, imperfections, transient

Abstract
Welding is a major joining technique employed in hi-tech industries like in nuclear, aerospace and aeronautical, submarine and shipbuilding and pressure vessel applications for the production of high performing resilient structures. The problems of weld induced imperfections like residual stresses and shape change behavior evolve almost simultaneously with the introduction of welding as a joining method and harmful stresses in metals due to welding were reported in 1892 by Slavianov in his work. Tremendous efforts were made in the last couple of decades showing remarkable development in new welding technologies for defect free resilient structures capable of excellent in-service thermal and structural load bearing features. Despite these considerable technological innovations in high temperature joining technologies, the problems of weld induced imperfections like residual stresses and distortions is still a major challenge for the welding engineers due to the complex nature of the welding phenomenon.
Thin cylindrical shell structures constitute an important class of axis-symmetric structures and are exceptionally utilized in most of the high-tech domains. Therefore, the reliability of materials and structures in the form of thin-walled cylindrical structures is of paramount importance in aerospace, marine, aeronautical structures, pressure vessels and nuclear engineering applications. A number of longitudinal and circumferential welds are the mandatory integrating technique available for hi-tech applications like missile casing, nuclear reactors and pressure vessels, where specific strength and cost effectiveness are the major design constraints. These welds are
commonly produced by single or double "V" joint configuration penetrations and single or multiple runs arc welding processes. Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) process are the obvious selection in this regards due to excellent weld joint features. Low alloy steels (may or may not requiring post weld strengthening heat treatments depending upon the in-service loadings) along with stainless steels are the potential candidate materials.
Transient temperature distributions during Gas Tungsten Arc Welding (GTAW) process and subsequent cooling of the weldments have significant effect on the microstructures, physical properties, residual stress distributions and development of weld solidification cracks. The primary driving forces for most of the weld induced imperfections are the transient temperature distributions followed by transient and residual stress fields. In the present research dissertation, transient temperature distributions, transient/residual stress fields and distortion patterns for circumferentially welded thin-walled cylinders of low carbon steel and stainless are investigated in detail. A hybrid numerical simulation and experimental based analysis approach is employed. The simulations strategy is developed and implemented by using commercial available general purpose finite element software ANSYSŪ enhanced with a number of author written subroutines. The moving heat sources, material deposition, temperature dependent material properties, metal plasticity and elasticity, transient heat transfer and mechanical analyses are included. One-way thermo-mechanical coupling is assumed i.e. de-coupled thermo-mechanical analysis in which the thermal analysis is completed first, followed by a separate mechanical analysis based on the thermal history. As part of an integrated effort to model and predict GTA welding process, a series of single-pass experiments for butt-joint configurations in thin-walled cylinders is conducted on robotized tungsten inert gas welding equipment.
This dissertation therefore, presents the development of an experimental and numerical approach to the analysis of circumferentially arc welded thin-walled cylinders. The investigation jointly relies on the finite element analysis and the experimentation and shows a good co-relation between the simulation and experimental work with close agreement to the previously published literature (where applicable and cited).

Download Full Thesis
13,213 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 CONTENTS

 

ix
91.1 KB
2

1

INTRODUCTION

1.1 Introduction

1.2 Motivation for the Research

1.3 Scope and Objectives of the Research

1.4 Research Approach

1.5 General Conventions

1.6 Thesis Outline

1
227 KB
3 2 AN OVERVIEW OF HISTORICAL RESEARCH ISSUES IN COMPUTATIONAL WELD MECHANICS

2.1 Introduction

2.2 Numerical Simulations of Welding Phenomenon

2.3 Previous Contributions in Computational and Experimental Work Pertaining to Circumferential Welding

2.4 Concluding Remarks

12
1,352 KB
4 3 RECIPE FOR WELDING SIMULATIONS IN PRESENT RESEARCH

3.1 Introduction

3.2 Analytical Model for Thermal of Arc Welding

3.3 Finite Element Formulation

3.4 Physics Behind the Arc

3.5 Different Fields and Their Interaction

3.6 Heat Source Modeling

3.7 Heat Source Efficiency

3.8 Modeling of Heat Losses

3.9 Material Models in the Present Research

3.10 Filler Metal Deposition

3.11 Simulation Approach in ANSYS

47
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5 4 WELDING INDUCED STRESSES AND DISTORTIONS

4.1 Introduction

4.2 Finite Element Discretization

4.3 Other Simulation Aspects

4.4 Experimental Investigations

4.5 Thermal Effects of Welding

4.6 Welding Residual Stress Fields

4.7 Welding Distortions

4.8 Concluding Remarks

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1,143 KB
6 5 DETAILS OF EXPERIMENTAL SETUP AND PROCEDURES ADOPTED TO VALIDATE FE Model's

5.1 Introduction

5.2 Experimental Setup for Welding in Present Research

5.3 FE Model Validation

5.4 Error of Experimental Equipments

5.5 Concluding Remarks

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7 6 EFFECTS OF WELDING PROCESS PARAMETERS, GEOMETRIC PARAMETERS, JOINT ROOT OPENINGS AND TACK WELD ORIENTATIONS

6.1 Introduction

6.2 Details of Parametric Studies in this Chapter

6.3 Effects of Welding Speed

6.4 Effects of Heat Input

6.5 Effects of Cylinder Outer Diameter

6.6 Effects of Cylinder Wall Thickness

6.7 Effects of Joint Root Opening

6.8 Effects of Tack Weld Orientation

6.9 Concluding Remarks

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8 7 MITIGATION OF WELD INDUCED RESIDUAL STRESSES BY MECHANICAL STRESS RELIEVING (MSR)

7.1 Introduction

7.2 Present Study

7.3 MSR Analysis Procedure

7.4 As Welded Residual Stress Fields

7.5 Effects of Different MSR Treatments

7.6 Effectiveness of Different MSR Treatments

7.7 Concluding Remarks

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9 8 EFFECTS OF VARYING STRUCTURAL BOUNDARY CONDITIONS (WELDING FIXTURES) ON RESIDUAL STRESS FIELDS AND DEFORMATIONS

8.1 Introduction

8.2 Present Study

8.3 Finite Element Discretization

8.4 Experimental Validation

8.5 Welding Deformations

8.6 Welding Stresses

8.7 Concluding Remarks

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10 9 CONCLUSIONS AND RECOMMENDATIONS

9.1 Conclusions

9.2 Recommendations

Appendices

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471 KB