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Welding deformation analysis based on improved equivalent strain method to cover external constraint during cooling stage
냉각 시 외적 구속 조건을 고려한 개선된 등가변형도법 기반 용접 해석에 관한 연구

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dc.contributor.advisor장범선-
dc.contributor.author김태준-
dc.date.accessioned2017-07-13T08:59:40Z-
dc.date.available2017-07-13T08:59:40Z-
dc.date.issued2014-02-
dc.identifier.other000000017426-
dc.identifier.urihttps://hdl.handle.net/10371/120003-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 조선해양공학과, 2014. 2. 장범선.-
dc.description.abstractThe prediction and control of welding deformation at design stage has been an essential task in shipbuilding industry to ensure high fabrication quality as well as high productivity.
The most widely used method is the thermal elasto-plastic analysis method due to its high accuracy in the simulation results. However, it has a disadvantage in computational time due to the consideration of non-linearity of material and temperature-dependent material properties. In order to overcome the difficulties, a few efficient approaches which are applicable to complicated welding process of ship hull blocks have been developed.
In the present study, the existing equivalent stain method is improved to make up for its weaknesses. The improved inherent strain model is built considering more sophisticated three dimensional constraints which are embodied by six cubic elements attached on three sides of a core cubic element.
From a few case studies, it is found that the inherent strain is mainly affected by the changes in restraints induced by changes of temperature-dependent material properties of the restraining elements. On the other hand, the degree of restraints is identified to be little influential to the inherent strain. Thus, the effect of temperature gradients over plate thickness and plate transverse direction normal to welding is reflected in the calculation of the inherent strain chart.
A 3D contour of inherent strain is plotted versus temperature gradients of thickness direction and transverse direction for a maximum welding temperature value. A series of inherent strain charts are obtained varying the maximum welding temperature value. The welding deformation can be calculated by an elastic FE analysis using the inherent strain values taken from the inherent strain chart.
The proposed method is verified by comparing the calculated welding deformation analysis results with the existing method, thermal elasto-plastic FE analysis, and experimental results.
External restraints imposed normal to plate during cooling stage is identified to be effective to the reduction of angular distortion of butt-welded or fillet-welded plate. The external restraint is represented by vertical force on work piece at both sides and bending stress forms in transverse direction. The additional bending stress distribution across plate thickness is reflected into the improved inherent strain model and a set of inherent strain charts with different levels of bending stress are newly calculated. Welding deformation can be calculated from an elastic linear FE analysis using the inherent strain values taken from the chart and compared with those from a 3D thermal elatsto-plastic FE analysis.
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dc.description.tableofcontents1. Introduction 1
1.1. Background of this study 1
1.2. Research Status 2
1.3. Objectives 7
1.4. Organization 7
2. Equivalent strain method based on inherent strain 9
2.1. Definition of the inherent strain 9
2.2. Welding analysis based on inherent strain 11
2.3. Calculation of the inherent strain in a previous equivalent strain method 14
2.3.1. Simplified inherent strain model for equivalent strain method 14
2.3.2. Inherent strain chart for equivalent strain method 17
2.3.3. Distribution of the highest temperature 18
2.3.4. Calculation of degree of restraint 19
3. Limitation of equivalent strain method in previous study 20
3.1. Absence of consideration of the temperature distribution 20
3.2. Repetitive calculation of degree of restraint 27
3.3. Strain input 29
4. Improved equivalent strain method considering the temperature distribution 33
4.1. Improved solid-spring model 33
4.1.1. Restraint positions of solid-spring model 34
4.1.2. Boundary condition of solid-spring model 37
4.1.3. Calculation of elastic modulus of the periphery elements 40
4.2. Degree of restraint determination 46
4.2.1. Inherent strain of the elements subjected to tri-axial stress 46
4.2.2. Degree of restraint in room temperature 52
4.2.3. Changes in degree of restraint due to temperature 55
4.3. Inherent strain chart considering temperature gradient 58
4.3.1. Definition of thermal gradient TG 58
4.3.2. Application of TG to welding model 60
4.3.3. Inherent strain chart 62
4.4. Strain input 67
4.5. Welding analysis procedure based on improved equivalent strain method 69
4.6. Summary of comparison with the previous study 70
5. Welding analysis using improved equivalent strain method 72
5.1. Butt welding 72
5.1.1. Comparison of 6mm plate 76
5.1.2. Comparison of 10mm plate 79
5.1.3. Comparison of 15mm plate 82
5.1.4. Comparison of 20mm plate 85
5.1.5. Summary and discussion 88
5.2. Fillet welding 92
5.2.1. Comparison of 8mm plate 95
5.2.2. Comparison of 15mm plate 98
5.2.3. Comparison of 18mm plate 101
5.2.4. Summary and discussion 104
6. Welding analysis considering external constraint during cooling 108
6.1. The effect of external constraint in welding 108
6.2. Simplifying of welding analysis considering external constraint during cooling 110
6.3. Identification of assumption 117
6.4. Inherent strain model considering external constraint during cooling 118
7. Comparison of the welding analysis considering external constraint during cooling stage 123
7.1. Analysis considering various external force 123
7.2. Analysis of model related to external force inducing equal bending moment 129
8. Comparison of analysis time 138
9. Conclusion 140
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dc.formatapplication/pdf-
dc.format.extent5863005 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectWelding deformation-
dc.subjectInherent strain-
dc.subjectEquivalent strain-
dc.subjectExternal Constraint-
dc.subject.ddc623-
dc.titleWelding deformation analysis based on improved equivalent strain method to cover external constraint during cooling stage-
dc.title.alternative냉각 시 외적 구속 조건을 고려한 개선된 등가변형도법 기반 용접 해석에 관한 연구-
dc.typeThesis-
dc.contributor.AlternativeAuthorWelding Deformation Analysis based on Improved Equivalent Strain Method to cover External Constraint during cooling Stage-
dc.description.degreeDoctor-
dc.citation.pages140-
dc.contributor.affiliation공과대학 조선해양공학과-
dc.date.awarded2014-02-
Appears in Collections:
College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Naval Architecture and Ocean Engineering (조선해양공학과)Theses (Ph.D. / Sc.D._조선해양공학과)
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