Analysis of residual stresses caused by welding in plates with opening and hardening

Number of pages: 143 File Format: word File Code: 31464
Year: Not Specified University Degree: Master's degree Category: Civil Engineering
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  • Summary of Analysis of residual stresses caused by welding in plates with opening and hardening

    Structural Master's Thesis

    Abstract

    In the welding process, after a stage of cooling the object, due to the uneven distribution of temperature, there remain stresses in it, which are called residual stresses. To obtain these stresses, the temperature history of the object during the welding process must be available. For this purpose, first a thermal analysis is done to obtain the temperature history of the object. By having a temperature history and performing a mechanical analysis, the residual stresses and deformations are obtained.

    In this research, using the nonlinear finite element method in the ANSYS software, the thermal and mechanical analysis of the weld was performed for the plates with openings and hardeners, and the residual stresses were obtained. The results show that due to the presence of expansion and hardening in the plates, the amount of residual stresses caused by welding may change by 30%. Examining the effect of the distance of the hardener from the weld axis shows that by increasing this distance up to 6 times the thickness of the plate, the residual stresses are reduced and from this distance onwards, the hardener does not have much effect in reducing the residual stresses. According to the results, it can be seen that by choosing a hardener with the same cross-sectional area but with a greater thickness, the amount of residual stress is reduced by about 20%. The investigation of residual stresses in plates with openings and hardeners of different dimensions shows that the ratio of the dimensions of the plates has no effect on the amount and location of the maximum residual stresses. Keywords: welding residual stresses, thermal analysis, mechanical analysis, plates, openings, hardeners. available)

    1-3 Electric arc welding with coated electrode

    In this method, the heat required for welding is obtained from the electric arc created between the electrode and the work piece. The tip of the electrode, the molten welding pool, the arc and the welding position on the work piece are protected by the shielding gas resulting from the breakdown and combustion of the electrode coating; But the protection from this gas is not complete compared to GTAW and GMAW methods due to the lack of proper shielding gas flow, and additional protection of the molten pool is done by molten slag. The equipment used in this method is a power source, welding tongs, connecting cables and electrodes. The electrodes used in this method have very different chemical compositions from the steel core and also very diverse types in terms of weight and coating material. The thickness of the part, the welding condition and the type of connection determine the electrode diameter. The general form of naming the electrodes is EXX(X)XX. The letter E indicates the electrode, the first two (or three) digits indicate the minimum tensile strength of the weld metal in terms of ksi (kilopounds per square inch), the next digit indicates the welding position, the number 1 is suitable for welding in all positions, 2 for welding in flat and horizontal positions, and 4 for all positions except vertical head up. The last digit depends on the material of the coating and its applicability, and also specifies the type of flow that can be used. The equipment used in this method is shown in Figure 5-1 [2].

    1-4 Dissertation Organization

    In this thesis, the welding process, the residual stresses caused by welding and the investigation of the effect of residual stresses in plates with opening and hardening are discussed. The first chapter is dedicated to the introduction of welding, welding joints and welding methods. In the second chapter, the method of deriving the equations governing the thermal and mechanical behavior of welding and the causes of residual stresses and deformations in the welding process are explained. In the third chapter, the research background on welding, stresses and residual deformations caused by it are examined. In the fourth chapter, how to model the welding process, verification and how to extract residual stresses using ANSYS software are described. In the fifth chapter, the residual stresses caused by welding in the plates with openings are discussed first, and then the effect of the residual stresses on the behavior of these plates is analyzed. In the sixth chapter, the residual stresses caused by welding in plates with hardeners are discussed. In the seventh chapter, conclusions and suggestions for future research are given. Chapter Two: Thermal and mechanical analysis of welding. 2-1 Preface: There are two methods for modeling a weld.. The first method is the direct coupler, in which a component capable of thermal and mechanical analysis is used to model the weld. The second method is the non-couple method in which two separate analyzes are performed. First, a thermal model is created and a heat transfer analysis is performed. Because the heating in the welding process is temporary and the location and amount of this heat changes with time, so this thermal analysis must be a transient analysis and because the data values ??of the problem change according to the thermal changes in the part, so the mentioned thermal analysis is a nonlinear analysis. From this analysis, the temperature history is determined. The second model, which uses the results of the temperature history obtained from the first analysis as thermal load, is a mechanical analysis that gives residual stresses and deformations caused by welding.

    In this chapter, the basics of thermal and mechanical analysis are discussed.

    Analysis of Welding Residual Stresses in Plates with Openings and Stiffeners

     

     

     

    Abstract

    Residual stresses are defined as stresses remaining in a body after cooling phase in welding operation. To evaluate these stresses, the temperature history of the body during the welding process must be available. In this thesis, nonlinear finite element software (ANSYS) was used to obtain residual stresses resulting from welding process in plates having openings and stiffeners. In this work, thermal and mechanical analysis of weld were carried out to investigate the residual stresses. The thermal analysis led to obtain thermal history of the plates, which was used as loading in mechanical analysis. The results show that in the presence of openings and stiffeners, the amount of welding residual stresses may be changed by 30 percent. The effect of stiffener distance from the welding axis shows that by increasing the distance to 6 times of plate thickness, residual stresses are reduced and for the greater distances, stiffeners have no effect on the amount of residual stresses. According to the results, it has been observed that by choosing stiffeners with the same area, but with more thicknesses, the residual stresses are decreased to 20 percent.  Evaluation of residual stresses in plates with openings and stiffeners with different sizes show that dimension ratios of plates have no effect on the amount and location of the maximum tensile residual stresses.

    Keywords: Welding Residual Stresses, Thermal Analysis, Mechanical Analysis, Plates, Openings, Stiffeners.

  • Contents & References of Analysis of residual stresses caused by welding in plates with opening and hardening

    List:

     

    Chapter One - Introduction

    1

    1-1 Preface

    1

     

    1-2 Basics of welding

    3

     

    1-2-1 Definition of welding

    3

     

    1-2-2 types of welding joints

    3

    1-2-3 types of welding

    4

    1-2-4 groove welding

    5

     

    1-3 electric arc welding with coated electrode

    6

    1-4 Dissertation organization

    7

     

     

     

    Chapter Two - Thermal and Mechanical Analysis of Welding

    8

     

    2-1 Preface

    8

    2-2 Thermal Analysis

    9

    2-2-1 heat source

    12

     

    2-2-1-1 heat source efficiency

    12

     

     

    2-2-1-2 heat flux caused by the welding arc

    13

    2-2-1-3 Heat production rate

    17

     

    2-2-2 properties of matter in thermal analysis

    18

     

    2-2-3 phase change

    18

     

    2-2-4 boundary conditions

    21

    2-2-4-1 displacement heat loss

    21

     

    2-2-4-2 radiation heat transfer

    22

     

    2-2-4-3 heat flux

    22

    2-2-5 thermal analysis results

    23

    2-3 mechanical analysis

    24

    2-3-1 nonlinear analysis method in finite element method

    25

     

    2-3-1-1 Newton-Raphson method

    26

    2-3-2 material properties in analysis Mechanical

    28

     

    2-3-3 results of mechanical analysis

    29

     

    2-4 stresses caused by welding

           29

     

     

     

     

     

    Chapter three - stresses Residual due to welding (theoretical basics and history) 33 3-1 Preface 33 3-2 Longitudinal residual stresses due to welding 35 3-3 Transverse residual stresses due to welding

    40

     

    3-4 methods of determining residual stresses caused by welding

    44

    3-5 Investigating the history of the effect of a welding sequence on residual stresses caused by welding

    49

    3-5-1 History of thermal analysis

    51

    3-5-2 History of mechanical analysis

    52

     

    3-5-3 simulation results

    52

     

    3-5-4 comparison of results

    54

    3-6 simulation results of welding residual stress

    56

     

    3-7 Effect of welding direction on residual stress in multi-pass welding (one groove)

    59

     

    3-8 Residual stresses caused by welding for thick sheet with double-sided V-shaped groove

    61

     

     

    Chapter 4 - Modeling the welding process in ANSYS

    70

    4-1 Preface

    70

     

    4-2 Specifications required for analysis

    70

     

    4-2-1 Work piece geometry

    70

    4-2-2 Material Properties

    71

     

    4-2-3 Heat Source Characteristics

    72

     

    4-3 Thermal Analysis

    72

     

    4-3-1 Thermal Component

    73

    4-3-2 method of birth and death of components

    75

    4-3-3 thermal analysis results

    77

    4-4 mechanical analysis

    79

    4-4-1 mechanical component

    80

    4-4-2 modeling of residual stresses

    80

    4-4-2-1 Effects of meshing on residual stress results

    81

    4-4-2-2 Longitudinal residual stresses

    83

    4-4-2-3 Lateral residual stresses

    84

    Chapter Five - Opening plates

    86

    5-1 Preface

    86

    5-2 Specifications required for analysis

    86

    5-2-1 Work piece geometry

    86

    5-2-2 Material properties

    87

    5-3 Analysisp>87

    4-5 mechanical analysis

    91

    5-5 effect of plate dimensions on residual stresses

    93

     

    Sixth chapter - Plates with hardening

    96

    6-1 Preface

    96

    6-2 specifications required for analysis

    96

    6-2-1 geometry of the workpiece

    96

    6-2-2 material properties

    97

    6-3 thermal analysis

    97

    6-4 mechanical analysis

    101

    6-5 Effect of plate dimensions on residual stresses

    102

    6-6 Effect of hardeners dimensions on residual stresses

    103

    6-7 Effect of distance of hardener from welding axis on residual stresses

    106

    6-7-1 Work piece geometry

    106

    6-8 Plates with expansion and hardening combination

    109

    6-8-1 Thermal analysis

    110

    6-8-2 Residual stresses in plates with expansion and hardening combination

    111

     

    Chapter Seven – Conclusion and suggestion for further research

    112

    7-1 Preface

    112

    7-2 Results

    113

    7-3 Suggestions for further research

    114

    References

    115

    Source:

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Analysis of residual stresses caused by welding in plates with opening and hardening