• 한국강구조학회 논문집
• /
• 제12권2호통권45호
• /
• pp.111-122
• /
• 2000

이 연구에서는 덮개판 형상이 피로특성에 미치는 영향을 정량적으로 평가하기 위해서 강교량을 구성하는 구조세목 중 덮개판 필렛용접부를 대상으로 일련의 피로실험을 실시하였다. 피로실험결과 덮개판 형상에 따라 피로강도에 다소 차이를 나타내고 있었으나 국내 및 외국의 피로설계기준을 만족함을 알 수 있었다. 또한 비치마크실험결과로부터 피로균열 발생점은 용접지단부의 형상에 밀접하게 관련되어 있음을 확인할 수 있었으며, 용접지단부의 여러 곳에서 동시다발적으로 발생한 피로균열이 반타원형의 표면균열의 형태로 성장하고 이 균열이 서로 합체되어 관통균열의 형태로 성장함으로써 결국 파단에 이르렀다. 한편, 파괴역학적 해석결과로부터 기존의 제안식 및 유한요소해석에서 구한 균열보정 계수 중기하학적형상보정계수가 가장 지배적임을 알 수 있었으며, 피로균열성장속도와 유한요소해석에서 구한 응력확대계수범위 사이의 관계로부터 덮개판 필렛용접부의 피로수명을 산정 할 수 있었다.

• Geomechanics and Engineering
• /
• 제32권5호
• /
• pp.513-521
• /
• 2023

Temperature is one of the most critical elements that influence the rutting and fatigue resistance of flexible pavements. Particularly in extreme hot regions in Saudi Arabia, high temperature would significantly reduce the rutting resistance of flexible pavements leading to reduction of pavement service life. Due to the impacts of global warming, average temperature in Saudi Arabia is expected to further increase by about 4℃ by the end of the 21st century. The substantial increase in average temperature will elevate the expected pavement maintenance and rehabilitation cost. This paper analyzes the structural effects of temperature on pavement using layered elastic analysis based on finite element techniques. The research team calculated the potential loss of pavement service life due to the projected temperature increase and climate change. The paper also analyzed potential impact of using carbon waste in asphalt concrete to tackle the derogatory impacts of temperature rise.

• Journal of Advanced Research in Ocean Engineering
• /
• 제3권3호
• /
• pp.112-124
• /
• 2017

As an LNG carrier preserves and transports liquefied natural gas under minus $163^{\circ}C$, the cargo tank has to have sufficient hull strength against not only the wave loads but also against loads caused by loading and unloading and thermal expansion to keep the LNG safely. The main insulation types for a CCS are No.96 and Mark III from GTT for the membrane LNG carrier. Particularly, the invar membrane plate in No.96 is very thin and its connections could experience high local stresses owing to such dynamic loads. Therefore, it should be verified whether those connections have sufficient fatigue lives for the purpose of operation and maintenance. This research aims at performing fatigue analysis with 0.1 fatigue damage criteria for 40 years of design life to support new membrane CCS development using proper S-N curves and the associated finite element modeling technique for each connection and then propose a reasonable design methodology.

• Journal of Welding and Joining
• /
• 제17권6호
• /
• pp.32-37
• /
• 1999

Since stainless steel plates have good mechanical properties, weldability, appearance and resistance of corrosion, these are traditionally used for vehicles such as the bus and the train. And they are mainly fabricated by spot welding. But fatigue strength of their spot welded joint is considerably influenced by welding conditions as well as geometrical factors. Thus a reasonable and systematic criterion for long life design of spot welded body structure must be established. In this report, strain energy density was analyzed by using 3-dimensional finite element model about the IB-type spot welded lap joint under tension-shear load. Fatigue tests were conducted on them having various thickness, joint angle, lapped length and width. From their results, it was found that fatigue strength of the IB-type spot welded lap joints could be effectively and systematically rearranged by strain energy density at the edge of nugget.

• Structural Monitoring and Maintenance
• /
• 제6권4호
• /
• pp.291-315
• /
• 2019

Fatigue cracks are inevitable in circumstances in which the cyclic loading exists. Therefore, many of mechanical components are in a risk of being in exposure to fatigue cracks. On the other hand, renewing the facilities or infrastructures is not always possible. Therefore, retrofitting the structures by means of the available methods, such as crack arrest methods is logical and in some cases inevitable. In this regard, this paper considers three popular crack arrest methods (e.g., drilling stop-hole, steel welded patch, and carbon fiber reinforced (CFRP) patch), which have been compared by using extended finite element method (XFEM). In addition, effects in terms of the width and thickness of patches and the configuration of drilling stop holes have been evaluated. Test results indicated that among the considered methods, CFRP patches were the most effective means for arresting cracks. Besides, in the case of arresting by means of drilling stop holes, drilling two holes next to the crack-tip was more effective than blunting the crack-tip by drilling one hole. In other words, the results indicated that the use of symmetric welded metal patches could lead to a 21% increase in fatigue life, as compared to symmetric stop holes. Symmetric CFRP patches enhanced the fatigue life of cracked specimen up to 77%, as compared to drilling symmetric stop holes. In addition, in all cases, symmetric configurations were far better than asymmetric ones.

• International Journal of Korean Welding Society
• /
• 제1권1호
• /
• pp.51-57
• /
• 2001

Effect of the joint details on the stress distribution over a slot structure has been studied in order to improve its fatigue life using a finite element analysis. The joint details of interest are the radius and height of scallop at the stiffener as well as the mis-alignment between the stiffener and longitudinal member. For a slot structure currently used, the stiffener heel is subjected to the maximum stress for a given external load, where is a potential fatigue crack initiation site. The stresses at the stiffener heel and toe decrease both by increasing the scallop radius and more significantly by increasing the mis-alignment while no notable effect of the scallop height on it is appreciated. A proper combination of these factors makes it possible to reduce the stresses at the stiffener heel and In, theoretically, more than 50%. This is attributed to the modification of the stress distribution over the slot structure including the transition of the maximum stressed region from the stiffener heel to the slot surface of the transverse web. Such then results in a g[eat improvement of the fatigue life of the slot structure.

• Journal of Welding and Joining
• /
• 제14권2호
• /
• pp.36-45
• /
• 1996

Fatigue strength of the spot welded lap joint is considerably influenced by corrosive environments. Particularly, the chloride and the sulfide are most injurious to strength of the spot welded lap joint. Therefore, there is a need to evaluate its effect to corrosion fatigue strength for safe life design of spot welded structures. In order to evaluate their corrosion fatigue strength, corrosion fatigue tests on the spot welded lap joints of the uncoated and the coated high strength steel sheets were conducted in air and in 10% NaCl solution. Corrosion fatigue strength of the uncoated specimens were entirely lower than the coated one in NaCl solution, but those of the coated specimens in NaCl solution were lower than in air. And stress distribution in single spon welded lap joint subjected to tension-shear load was investigated by the finite element method. Using these results, we tried to evaluate corrosion fatgue strength of the various spot welded lap joints with maximum stress $\sigma_{max}$ at edge on loading side of the spot welded lap joint. We could find that corrosion fatigue strength could be quantitatively and systematically rearranged by $\sigma_{max}$.

• Steel and Composite Structures
• /
• 제39권4호
• /
• pp.453-469
• /
• 2021

The cracking at the transverse diaphragm cutout is one of the most severe fatigue failures threatening orthotropic steel decks (OSDs), whose mechanisms and crack treatment techniques have not been fully studied. In this paper, full-scale experiments were first performed to investigate the fatigue performance of polished cutouts involving the effect of an artificial geometrical defect. Following this, comparative experimental testing for defective cutouts strengthened with carbon fiber-reinforced polymer (CFRP) was carried out. Numerical finite element analysis was also performed to verify and explain the experimental observations. Results show that the combinative effect of the wheel load and thermal residual stress constitutes the external driving force for the fatigue cracking of the cutout. Initial geometrical defects are confirmed as a critical factor affecting the fatigue cracking. The principal stress 6 mm away from the free edge of the cutout can be adopted as the nominal stress of the cutout during fatigue evaluation, and the fatigue resistance of polished cutouts is higher than Grade A in AASHTO specification. The bonded CFRP system is highly effective in extending the fatigue life of the defective cutouts. The present study provides some new insights into the fatigue evaluation and repair of OSDs.

• 국제강구조저널
• /
• 제18권5호
• /
• pp.1589-1597
• /
• 2018

Fatigue tests and numerical analysis were carried out to evaluate the fatigue performance at the U-rib to deck welded joint in steel box girder. Twenty specimens were tested corresponding to different penetration rates (80 and 100%) under fatigue bending load, and the fatigue strength was investigated based on hot spot stress (HSS) method. The detailed stress distribution at U-rib to deck welded joint was analyzed by the finite element method, as well as the stress intensity factor of weld root. The test results show that the specimens with fully penetration rate have longer crack propagation life due to the welding geometry, resulting in higher fatigue failure strength. The classification of FAT-90 is reasonable for evaluating fatigue strength by HSS method. The penetration rate has effect on crack propagation angle near the surface, and the 1-mm stress below weld toe and root approves to be more suitable for fatigue stress assessment, because of its high sensitivity to weld geometry than HSS.

• Composites Research
• /
• 제17권4호
• /
• pp.68-73
• /
• 2004

본 논문에서는 한 쪽 면만 복합재 패치로 보강한 알루미늄 균열평판의 피로균열 진전거동을 해석적인 방법으로 고찰하였다. 한쪽 면 보강 시, 균열선단은 비대칭성과 면 외 굽힘의 효과로 인하여 초기의 직선형태에서 경사곡선형태로 진전한다는 사실을 이전의 연구견과에서 확인할 수 있다. 따라서 정확한 피로거동을 고찰하기 위하여는 이와 같은 균열선단의 변화과정을 예측하고, 이론 해석에 반영하는 것이 필수적이라 하겠다. 본 연구에서는 균열선단 전개형상을 고려한 한쪽 면 보강시의 피로해석을 수행하기 위하여 선형탄성 파괴역학개념을 적용한 3차원 순차적 유한요소 해석기법을 적용하였는데, 이를 통하여 진전하는 균열선단 형상을 단계적, 반복적으로 추적하고 해석모델에 반영하였다. 이와 같은 해석기법을 적용함으로써 패치보강 평판의 피로수명은 물론 균열선단 진전과정도 정확히 예측할 수 있었다. 해석으로 얻어진 균열선단 진전거동 및 피로수명은 상응하는 실험결과와 잘 일치함을 확인하였다.