TIG처리에 따른 하중비전달형 필렛용접부의 피로특성

정영화,경갑수,홍성욱,김익겸,남왕현,Jung, Young Hwa,Kyung, Kab Soo,Hong, Sung Wook,Kim, Ik Gyeom,Nam, Wang Hyone 한국강구조학회 2000 韓國鋼構造學會 論文集 Vol.12 No.5

이 연구에서는 하중비전달형 필렛용접부를 대상으로 순수휨상태에서 TIG 처리에 따른 피로강도 향상정도 및 피로특성을 정량적으로 평가하기 위해서 4점 휨실험을 실시하였다. 피로실험결과 용접후처리를 실시하지 않은 시험체는 국내 외에서 규정하는 피로강도등급을 만족하고 있고 TIG 처리한 시험체는 용접후처리를 실시하지 않은 시험체보다 $2{\times}106$회 피로강도가 상회하는 것을 알 수 있었다. 또한 비치마크실험결과 피로균열은 용접지단부의 비드접선각도 및 곡률반경이 최소로 되는 점에서 다발적으로 발생하며, 반타원형 균열로 성장, 합체되어 파단에 이르는 것을 확인할 수 있었다. 한편 유한요소해석결과 용접지단부의 응력집중계수는 용접지단부의 비드접선각도 및 곡률반경과 밀접한 관계가 있으며, 이 중에서 곡률반경이 용접지단부의 응력집중계수에 보다 큰 영향을 미치는 것을 알 수 있었다. 한편 파괴역학적 해석결과 a/t가 0.4 이하인 경우에 기하학적형상보정계수가 균열보정계수에 가장 지배적인 영향을 미치는 인자임을 알 수 있었다. 또한 유한요소해석결과로부터 산정한 응력확대계수범위와 피로균열성장속도의 관계식으로부터 피로수명을 비교적 정확하게 산정할 수 있었다. In this study, the 4-point bending test has been performed in order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength of as-welded specimens has been satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC, and fatigue strength at $2{\times}106cycles$ of TIG-dressing specimens has been increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks have been occurred at several points, where the radius of curvature and flank angle in the weld bead toes are low, and grown as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has been closely related to the flank angel and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has been largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

지간장에 따른 강판형 철도교의 피로피해도 평가

정영화,김익겸,김지훈,남왕현,Jung, Young-Hwa,Kim, Ik-Gyeom,Kim, Ji-Hun,Nam, Wang-Hyone 강원대학교 산업기술연구소 1999 産業技術硏究 Vol.19 No.-

Steel railway bridge gets vibration from moving load ; additionally, this kind of moving load is going to be a sufficient reason, which causes fatigue damage to steel railway bridge. Fatigue damage and stress curve were raised by moving load depends on span length in steel railway bridge. In other words, stress curve appears index regarding every axial load in short span, but self weight lets stress curve's change decrease in proportion to increasing span length. Thereby, we have studied that how the steel railway bridge appear fatigue damage in proportion to span length of steel railway bridge. Dynamic strain was measured in 4 steel plate-girder railway bridge during the trains was passing, which is located on the line of Kyoung-chun railway. And time history response analysis has been done in order to ensure actual survey. The results of this study show the decreased of the fatigue damage in steel railway bridge according to length of span. This paper ends is bases research of fatigue design in steel railway bridges according to span length.

용접구조용강재의 기계적 성질에 관한 통계적 분석

장동일,경갑수,홍성욱,남왕현,Chang, Dong-Il,Kyung, Kab-Soo,Hong, Sung-Wook,Nam, Wang-Hyone 한국강구조학회 2000 韓國鋼構造學會 論文集 Vol.12 No.3

본 연구에서는 강구조물에 자주 사용되고 있는 용접구조용강재를 대상으로 강재검사성적증명서를 수집하고 이를 통계적으로 분석, 정리해서 기계적 성질의 특성을 정량적으로 평가하였다. 본 연구결과 현재 국내에서 생산되는 용접구조용강재의 기계적 성질은 현행 KS에서 규정하고 있는 기준값을 만족하였으며, 판두께 및 강도등급과 일정한 상관관계가 있음을 알 수 있었다. 강종별 판두께 및 강도등급과 기계적 성질 사이에는 선형적인 비례관계가 성립, 본 연구결과는 기존 연구결과와 유사한 경향이 있음을 알 수 있었다. 현행 KS에서는 강재의 기계적 성질 중 항복점 응력에 대한 상한값이 규정되어 있지 않는데, 강재의 변형성능을 충분하게 확보하기 위해서는 항복비 (또는 항복강도)의 상한값을 규정 할 필요가 있을 것으로 생각된다. In this study, we have quantitatively estimated the mechanical properties of structural welding steels widely used in steel structures after correcting the millsheets of the steels using statistical technique. From this result, in present, the mechanical properties of the steels produced in domestics have satisfied the prescribed values in Korean Standards. The mechanical properties of the steels were dependent upon the plate thickness & class of the steels. Also, there have been linear relations between the plate thickness & class of the steels and the mechanical properties of the steels. And the results of this study have shown the similar tendencies with the existing results. Because the upper limit value of yield strength is not prescribed at Korean Standards in present, it is necessary to prescribe the upper limit value of yielding ratio(or yield strength) in order to assure the deformation performance of the steels.

국부가열을 이용한 면외거셋의 피로강도 향상

정영화(Jung Young Hwa),남왕현(Nam Wang Hyone),장동휘(Chang Dong Huy) 강원대학교 산업기술연구소 2001 産業技術硏究 Vol.21 No.1

This study is finding the most appropriate model of kangwondo watershed. To synthesize each hydrograph, It is found to several parameters which are used in existing hydrographes. then the synthestic hydrograph is compared and investigated wish many hydrographes of the rivers in kanwondo. These methods, Nakayasu, Clark, SCS are used to calculate the run-off of this watershed. When the calculated run-off is compared with real rating-curves, then it is found that the SCS method using the Clark’s concentrantion time is the best way on this area having large watershed, long river length and gentle water slope, the Nakayasu method is more suitable on this area having small watershed, short river length and steep water slope. Also it is founded from analyzing run-off hydrographes, peak run-off and peak time that the Clark’s method applied Kirpich’s concentration time way is suitable in the area of kanwondo.

SM570, POSTEN60 및 80 강재의 피로균열성장특성

정영화(Jeong Young Wha),김익겸(Kim lk Gyeom),강성립(Kang Sung Lib),남왕현(Nam Wang Hyone),김은성(Kim Eun Sung) 강원대학교 산업기술연구소 2001 産業技術硏究 Vol.21 No.1

In this study, a series of fatigue tests are carried out in order to estimate quantitatively the characteristics of fatigue crack growth rate for high strength steels of SM570, POSTEN60, and POSTEN80 steel, that is, the influence on fatigue crack growth rate according to the welding line, the characteristics of fatigue crack growth according to the welding method and the kinds of steel, and the characteristics of fatigue crack growth for base metal, heat affected zone and weld metal. From the test results, in case that the notch if parallel to welding line, it knows that the retardations of fatigue crack growth rate in crack tip at early stage increase remarkably than in case that the notch is perpendicular to welding line due to compressive residual stress. And the characteristics of fatigue crack growth rate according to welding method are that the dispersion of fatigue crack growth rate in case of FCAW method is smaller than that of SAW method. Also, it knows that the fatigue crack growth rate converges in high stress intensity factor range.

용접지단부 TIG처리에 의한 피로강도향상 및 피로특성

정영화(Jung Young Hwa),김익겸(Kim lk Gyeom),남왕현(Nam Wang Hyone),장동휘(Chang Dong Huy) 강원대학교 산업기술연구소 2000 産業技術硏究 Vol.20 No.1

The 4-point bending tests have been performed in order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for nonload-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture, As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely mechanics approaches, the crack correction factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4 from the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

하중비전달형 필렛용접부의 피로강도 향상법에 관한 연구 (2) : TIG 처리에 따른 영향

정영화(Jung Young Hwa),경갑수(Kyung Kab Soo),홍성욱(Hong Sung Wook),김익겸(Kim Ik Gyeom),남왕현(Nam Wang Hyone) 대한토목학회 2000 대한토목학회 학술발표회 논문집 Vol.2000 No.1

국부가열을 이용한 면외거셋의 피로강도 향상

정영화,남왕현,장동휘 江原大學校 産業技術硏究所 2001 産業技術硏究 Vol.21 No.B

In the study, the fatigue strength improvement and mechanism have been estimated by the Spot-Heating treatment on welded bead toes. For this, web-gusset specimens were made without residual stresses and the others with residual stresses imposed by Spot-Heating. The 4-point bending tests were performed in order to estimate the effect of spot-heating on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue test, fatigue strength of As-Welded specimen for non load-carrying fillet welded joints subjected to pure bending has satisfied the grade of fatigue prescribed in specifications of korea, AASHTO and JSSC. As compare with As-Welded specimen and Spot-Heating specimen have increased about 20% for the fatigue strength at 7.7×106 cycles. The Spot-Heating by reformation of the residual stress on welded bead toes has greatly affected the fatigue crack propagation life, but has slightly affected the fatigue crack initiation life.

용접지단부 TIG처리에 의한 피로강도향상 및 피로특성

정영화,김익겸,남왕현,장동휘 강원대학교 산업기술연구소 2000 産業技術硏究 Vol.20 No.A

The 4-point bending tests have been performed in order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for nonload-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture, As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely mechanics approaches, the crack correction factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4 from the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.