Effect of Surface Blast Treatment on Fatigue Behaviour of Out-of-Plane Gusset Welded Joints
- Alternative Title
- 도장용 블라스트 처리가 면외거셋용접 이음부의 피로거동에 미치는 영향
- Abstract
- Surface blasting prior to coating has been widely applied in built steel structures for cleaning forged surface and increasing adhesive property of applied coating components. The primary purpose of surface blasting application is to ensure a strong mechanical bond between the substrate and the coating by the enhanced roughness of the substrate material. It has been found that surface blast treatment significantly effects on fatigue behavior of welded joints. However, this effect is not considered in Fatigue Design Codes.
In this thesis, fatigue tests were carried out on five types of out-of-plane gusset fillet welded joints, including as-welded specimen, one-, two-, three-, and four-time blast-treated specimens (BT1, BT2, BT3, BT4), and then the effect of the surface blast treatment on the fatigue behaviour of the welded joints was studied. The radius of weld toe of BT1, BT2, BT3 and BT4 specimens increased 15%, 21%, 30% and 39%, in comparison with that of as-welded specimens, whereas the flank angle changed little. The tensile residual stress was induced on the surface of as-welded specimen while the compressive residual stresses were induced on the surface of blast-treated specimens. The fatigue test results showed that the fatigue life of the blast-treated specimens is longer than that of as-welded specimens in low stress ranges, even though there is no significant difference in fatigue life between the two types in high stress ranges. Over 167% increase in fatigue limit of BT1 specimen could be realized by using surface blast treatment. The fatigue test data of BT2 and BT3 specimens are distributed within the confidence lines (mean ± 2s lines) of BT1 specimens. This indicates that the fatigue lives of blast-treated specimens with different blasting times are almost same. Compressive residual stress induced on outer layer of specimen is supposed to play important role in increasing fatigue endurance limit of welded joints, while weld toe geometry improvement has minor effect in this process.
Prediction of fatigue crack propagation life was performed considering effect of compressive residual stress and redistribution of residual stress due to crack formation. Compressive residual stress will be included if the depth of crack is still smaller than the depth of compressive residual stress distribution. Once crack forms compressive residual stress will relieve and effect of compressive residual stress on fatigue crack propagation life gradually reduce. The beneficial effect of compressive residual stress disappears when crack depth exceeds the depth of compressive residual stress distribution. The fatigue crack propagation life results obtained with ratio of crack aspect of 0.3 and initial crack size of 0.03mm is nearly approximate with the fatigue test results in high stress range. However, there is difference between the fatigue limit obtained by fatigue tests and prediction. It is realized that the influence of crack aspect ratio on fatigue crack propagation life of welded joints is not significant.
Fatigue crack growth rate was calculated for as-welded specimen and blast-treated specimen (BT1) subjected to stress range of 150 MPa based on formula of Paris Law with modify to account for the threshold. The result shows that fatigue crack growth rate of blast-treated specimen is retarded in comparison with that of as-welded specimen. This is caused by compressive residual stress induced in blast-treated specimen. Fatigue crack growth was also investigated by size measurement of dye marking and beach marks formed by given number of cycles. The results indicated that fatigue crack growth of blast-treated specimens were slower than that of as-welded specimen.
- Author(s)
- Le, Van Phuoc Nhan
- Issued Date
- 2009
- Awarded Date
- 2009. 8
- Type
- Dissertation
- Keyword
- 피로거동 steel structures out-of-plane gusset welded joint fatigue life surface blasting
- Publisher
- 부경대학교 대학원
- URI
- https://repository.pknu.ac.kr:8443/handle/2021.oak/11244
http://pknu.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001955081
- Affiliation
- 부경대학교 대학원
- Department
- 대학원 토목공학과
- Advisor
- 이동욱
- Table Of Contents
- CHAPTER 1 GENERAL = 1
1.1 INTRODUCTION = 1
1.2 BACKGROUND = 4
1.2.1 FATIGUE FAILURE OF WELDED JOINTS = 4
1.2.2 FATIGUE LIFE = 11
1.2.2.1 Fatigue Crack Initiation Life = 13
1.2.2.2 Fatigue Crack Propagation Life = 13
1.2.3 FACTORS EFFECT ON FATIGUE STRENGTH OF WELDED JOINTS = 16
1.2.3.1 Effect of Weld Quality = 16
1.2.3.2 Effect of Size = 17
1.2.3.3 Effect of Residual Stress = 20
1.2.3.4 Effect of Surface Roughness = 21
1.2.3.5 Effect of Composition = 21
1.2.3.6 Effect of Post Weld Treatment = 23
1.3 OBJECTIVES = 23
1.4 SUMMARY = 24
CHAPTER 2 PREVIOUS RESEARCHES = 25
2.1 GENERAL METHODS FOR IMPROVING FATIGUE LIFE = 25
2.2 METHODS OF MODIFICATION OF WELD GEOMETRY = 26
2.3 METHODS OF MODIFICATION OF RESIDUAL STRESS DISTRIBUTION = 28
2.4 METHODS OF FATIGUE STRENGTH IMPROVEMENT APPLIED IN STEEL STRUCTURES = 36
2.4.1 Tungsten Inert Gas (TIG) Dressing Treatment = 36
2.4.2 Grinding Treatment = 38
2.4.3 Peening Treatment = 41
2.4.3.1 Hammer Peening Treatment = 41
2.4.3.2 Needle Peening Treatment = 42
2.4.3.3 Shot Peening Treatment = 43
2.4.4 Ultrasonic Impact Treatment (UIT) = 46
2.5 SURFACE BLAST TREATMENT = 48
2.6 SUMMARY = 54
CHAPTER 3 FATIGUE TESTS = 55
3.1 FATIGUE TEST 1 = 55
3.1.1 MATERIALS = 55
3.1.2 DETAIL OF SPECIMEN AND LOADING HISTORY = 56
3.1.3 RESULTS OF FATIGUE TEST = 58
3.2 FATIGUE TEST 2 = 60
3.2.1 MATERIALS = 60
3.2.2 DETAIL OF SPECIMEN AND LOADING HISTORY = 61
3.2.3 RESULTS OF FATIGUE TEST = 62
3.3 FATIGUE TEST 3 (BENDING TEST) = 65
3.3.1 MATERIALS = 66
3.3.2 DETAIL OF BEAM = 67
3.3.3 NOMINAL STRESS MEASUREMENT = 69
3.3.4 HOT SPOT STRESS (GEOMETRY STRESS) MEASUREMENT = 72
3.3.5 FATIGUE TEST PROGRAM = 78
3.3.6 RESULTS OF FATIGUE TESTS OF AS-WELDED AND BLAST-TREATED BEAMS = 80
3.4 WELD TOE PROFILE = 82
3.4.1 MEASUREMENT OF RADIUS AND FLANK ANGLE OF WELD TOE = 82
3.4.2 RESULTS OF RADIUS AND FLANK ANGLE OF WELD TOE = 82
3.5 RESIDUAL STRESS = 86
3.5.1 MEASUREMENT OF RESIDUAL STRESS = 86
3.5.2 RESULTS OF RESIDUAL STRESS = 86
3.6 FATIGUE CRACK INITIATION AND PROPAGATION = 88
3.6.1 FATIGUE CRACK OF OUT-OF-PLANE GUSSET WELDED JOINTS = 88
3.6.2 FATIGUE CRACK OF AS-WELDED BEAM AND BLASTTREATED BEAM = 92
3.7 SUMMARY = 98
CHAPTER 4 NUMERICAL ANALYSIS = 99
4.1 STRESS CONCENTRATION FACTOR = 99
4.1.1 Determination of Stress Concentration Factor by Experimental Formula = 99
4.1.2 Determination of Stress Concentration Factor by Finite Element Method (ANSYS Software) = 101
4.2 GENERAL METHOD EVALUATING FATIGUE LIFE OF WELDED JOINTS = 106
4.3 EFFECT OF WELD TOE GEOMETRY ON FATIGUE ENDURANCE LIMIT = 108
4.4 EFFECT OF RESIDUAL STRESS ON FATIGUE ENDURANCE LIMIT = 113
4.5 PREDICTION OF FATIGUE CRACK PROPAGATION LIFE CONSIDERING RESIDUAL STRESS = 116
4.5.1 METHOD OF PREDICTION OF FATIGUE CRACK PROPAGATION LIFE = 116
4.5.2 ILLUSTRATIVE EXAMPLE = 128
4.5.2.1 Results of Fatigue Life Prediction = 130
4.5.2.2 Comparison with Fatigue Test Results = 140
4.5.2.3 Effect of Ratio of Crack Aspect on Fatigue Life = 141
4.6 FATIGUE CRACK GROWTH RATE = 142
4.7 SUMMARY AND CONCLUSIONS = 144
CHAPTER 5 APPLICATION OF RESEARCH IN PRACTICE = 146
5.1 DESIGN CURVE = 146
5.1.1 DESIGN CURVE σ_(R) - N RELATIONSHIP DETERMINED BY BS 5400 = 146
5.1.2 DESIGN CURVE σ_(R) - N RELATIONSHIP DETERMINED BY IIW/IIS = 151
5.1.3 Design curve σ_(r) - N relationship determined by JSSC = 155
5.1.4 Design curve σ_(r) - N relationship determined by AASHTO = 157
5.2 APPLICATION IN FABRICATION = 159
CHAPTER 6 CONCLUSIONS = 161
APPENDICES = 164
A.3.5.1 Fracture sections of Out-of-Plane Gusset Welded Joints = 164
A.3.5.2 Crack 2 and Crack 3 of AW beam = 165
A.4.5.2 S-N curves of AW and BT1 specimens = 168
REFERENCES = 171
LIST OF PAPERS = 183
ACKNOWLEDGEMENTS = 185
- Degree
- Doctor
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