• 한국신뢰성학회지:신뢰성응용연구
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• 제17권1호
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• pp.50-57
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• 2017

Purpose : This paper is a comparative analysis results of the fatigue test for dental implants and accelerated life test by using a static type loading device commonly used in Korea and a dynamic type loading device (universal-joint) recommended by FDA. Methods : Fatigue tests of dental implant is based on ISO 14801 and classified into static load test and dynamic load test. The tests were carried out on three test specimens by four load stress steps under each loading device. For analysis on failure mode such as crack, fracture and permanent deformation of test specimens, we used X-ray three-dimensional computed tomography on test specimens before and after the fatigue tests. The design of the accelerated life test was based on the analysis results of the fatigue life data obtained from the dynamic load test and the statistical analysis software (Minitab ver.15) was used to analyze the appropriate life distribution. Results : As a result of the fatigue tests and the accelerated life tests at same acceleration condition under each test method, the fatigue life under the dynamic type loading device (universal-joint) was shorter than when static type loading device was applied. Conclusion : This paper can be used as a reference when the universal-joint type loading device for implants fatigue test is applied as ISO 14801.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7244-7249
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• 2015

본 연구는 소켓연결방식을 이용한 PSC 제형 거더를 구성하는 프리캐스트 부재의 소켓연결 성능을 검증하고 복부 부재의 최적화 단면을 산정할 수 있도록 단위부재 실험을 수행하여 거더의 구조성능을 평가하였다. 실험은 연결부의 성능실험과 복부의 휨 및 전단 성능 실험을 수행 하였으며 모두 4점 재하방식으로 수행되었다. 실험결과 소켓연결을 실시한 시험체에서의 초기균열하중은 기준시험체 대비 크게 저하 되었으나 최대하중 이후의 거동은 큰 차이가 없음을 알 수 있었다. 또한 철근의 고리 이음부 길이는 최대하중에 큰 영향을 미치지 않았다. 복부 전단 실험 결과 프리스트레싱 강봉으로 전단 보강을 실시한 시험체에서 기준시험체 대비 높은 사인장 균열하중을 나타내었다. 복부 휨 실험 결과 인장측에 프리스트레싱 강봉으로 보강한 시험체에서 가장 큰 최대하중 결과를 얻을 수 있었다.

• 한국지반공학회논문집
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• 제36권7호
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• pp.15-28
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• 2020

매입말뚝의 주면마찰력은 공벽에 주입되는 시멘트풀로 발휘되므로, 시멘트풀이 양생되기 이전에 수행되는 초기항타시험으로 매입말뚝의 주면마찰력을 평가할 수 없다. 또한, 재항타시험 시 항타에너지 부족으로 충분히 선단지지력이 발휘되지 않아 매입말뚝의 최종 지지력이 제대로 평가되지 않을 수 있다. 본 연구에서는 매입말뚝의 초기항타시험과 재항타시험의 결과를 조합하는 새로운 하중-침하량 곡선을 제안하고자 하였다. 현장에 시험말뚝을 매입말뚝공법으로 시공하였으며, 초기항타 및 재항타시험을 수행하고 동재하시험 결과에 대하여 CAPWAP(CAse Pile Wave Analysis Program) 분석을 수행하였다. 초기항타 시 선단 지지거동과 재항타 시 주면 지지거동을 조합한 말뚝 내 하중전이곡선을 가정하였으며, 하중-침하량 곡선을 새롭게 산정하였다. 또한 조합된 하중-침하량 곡선을 이용하여 시험말뚝의 지지력을 평가하였으며 이를 초기항타 및 재항타시험 결과와 비교 분석하였다. 분석 결과, 조합된 하중-침하량 곡선으로 산정된 지지력은 항타에너지 부족으로 인한 지지력 과소평가를 극복할 수 있는 것으로 나타났다. 또한, 가정된 하중전이곡선은 초기항타 및 재항타시험 결과와 비교했을 때 매입말뚝의 지지거동에 더 가까우므로, 조합된 하중-침하량 곡선을 이용함으로써 정재하시험 결과와 더 유사한 지지력을 산정할 수 있을 것으로 기대된다. 따라서, 본 연구에서 제안한 조합된 하중-침하량 곡선을 사용함으로써 매입말뚝의 동재하시험 시 지지력을 효과적으로 평가할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 가을 학술발표회 논문집
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• pp.82-87
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• 1992

In this thesis, the fatigue tests were performed on a series of SFRC (steel fiber reinforced concrete)to investigate the flexural tensile behavior of SFRC varying with the steel fiber contents and the steel fiber aspect ratios. Beam specimens of 10$\times$10$\times$60cm are used. the specimen series are classified according to the steel fiber contents varying 0.5. 1.0, 1.5%, and to the steel fiber aspect ratios varying 60, 80, 100. The three point loading system was used in the fatigue tests. The minimum value of repeated loading was fixed at 10.0kgf and maximum value was 75% to static ultimate strength for periodically using concrete strain gages located at the lower end of the mid-span, and the stress-strain curves were drawn for each specimens, respectively. From the tests result, it was found that the larger steel fiber content and the smaller the steel fiber aspect ratio is , the tensile strain of SFRC under fatigue load proportionally increases. By the regression analysis on these results, the empirical formulae to predict the tensile strain of SFRC were suggested. In comparison of the tensile elastic modulus under fatigue load, it was also found that the larger steel fiber content and the smaller steel fiber aspect ratio is , the smaller decreasing rate of the stiffness of SFRC under fatigue load decreased.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.801-808
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• 2007

Rotem Company has designed and manufactured bogie for Diesel Multiple Unit (DMU) according to the European standard UIC615-4, which si normally used for designing bogie frame. Because the countries located in Middle East do not have their own regulations for bogie design, most of running bogies in Middle East are designed by using European standard UIC615-4. UIC615-4 specifies the loads that bogie frame should withstand, indicates the way of material data to be used and the principles to be during verification by analysis and test. The bogie frame depends on the load conditions and magnitudes which are subjected to during service and characteristics of materials they are manufactured from. From the above reason, Rotem Company has performed Finite Element Analysis and load tests on the bogie frame according to UIC615-4. This research contains the results obtained by the analysis and the load tests. Also, this research verifies that the bogie frame has a static strength and fatigue strength. The analysis is carried out using I-DEAS 12 NX Series and specially designed test jigs and equipment are used for the load tests.

• 한국안전학회지
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• 제9권2호
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• pp.18-25
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• 1994

In this thesis, the fatigue tests were performed on a series of reinforced concrete to Investigate the variation of strength and the safety of reinforced concrete structures under fatigue load. The specimens were of the same rectangular cross-section, of effective height 24cm and width 30cm and their span was 330cm. The three point loading system is used in the fatigue tests. In these tests, the fracture mode of reinforced concrete structures under fatigue load, relationship between the repeated loading cycles and the mid-span displacement of the specimens were observed. According to the test results, the following fatigue behavior of reinforced concrete specimens were observed. By increasing of the number of repeated loading cycles, the mid-span displacement became greater, however the Incremental amounts of the displacement were reduced. It could be also known that the inelastic strain energy of the doubly reinforced rectangular beams was larger than that of the singly reinforced rectangular beams as increasing the number of repeated loading cycles. Compliance of reinforced concrete structures tended to be reduced as increasing the repeated loading cycles, and the compliance of the doubly reinforced rectangular beams was generally smaller than that of the singly reinforced rectangular beams. Based on the above investigation, it could be concluded that the doubly reinforced rectangular beams under fatigue load were more efficient to resist the brittle fracture than the singly reinforced rectangular beams.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.447-452
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• 2001

An automated system is developed to perform fatigue crack growth tests under constant effective stress intensity factor range ${\Delta}K_{eff}$. In the system, crack length and crack opening load are measured in real-time by using the unloading elastic compliance method. The system consists of two personal computers, an analogue electrical subtraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system. The performance of the developed system was tested and discussed performing constant ${\Delta}K_{eff}$ crack growth tests on a CT specimen of 7075-T6 aluminum alloy. The performance of the system is found to be strongly dependent on the accuracy of measurements of crack opening load. Besides constant ${\Delta}K_{eff}$ testing, the system is expected to be successfully applied for automation of various fatigue tests.

• 토지주택연구
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• 제11권2호
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• pp.75-86
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• 2020

As the urban regeneration project and the old housing maintenance project are actively progressing in Korea, small-scale building construction is being carried out in downtown areas. Small buildings in the downtown area are constructed on about 4 to 10 floors, and since they are carried out in small units in residential areas, it is difficult to enter large equipment to construct existing piles, and it is more vulnerable to complaints about noise and vibration. in this study, helical piles suitable for urban areas or small sites where it is difficult to enter large equipment, such as noise and vibration. Reliability analysis was performed on the results of the static load tests and dynamic load tests conducted at the LH site and the bearing capacity calculated by the hydrostatic method and the empirical formula (N value). As a result of comparing and analyzing the design formula and the results of static load test and dynamic load tests, the correlation between the design formula of the bored pile (Road bridge design standard) formula using N value and the design formula by the modified Davisson method frequently used by method commonly European helical file practitioners.

• 한국안전학회지
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• 제26권6호
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• pp.31-44
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• 2011

This paper has presented a finite element analysis of structural behaviour of box culvert during and after fires. The fire tests were carried out in a furnace on RC slabs using the ISO 834 standard fire curve. The load capacity after cooling of the RC slab that was not loaded during the fire tests was evaluated by means of additional 3 points bending tests. In the past, stress-strain models of concrete under fire loading have been proposed by several researchers. Comparisons are made with the load-displacement relations of RC slabs after fire loading using the existing stress-strain models with temperature, such as Schneider, EUROCODE 2, Lie, Shi and Nan model. By comparing the load-displacement relations, Lie model was found to result in a maximum load about 2.0% higher than that of test. Based on the fire test results of RC slabs, this paper presents an extensive analytical study on the fire response of box culvert during and after fires.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.3112-3121
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• 2021

One of the major factors affecting the life span of a Reactor Pressure Vessel (RPV) is the Pressurised Thermal Shock (PTS). PTS is a thermo-mechanical load on the RPV wall due to steep temperature gradients and structural load created by internal pressure of the fluid within the RPV. Safe operating life of a nuclear power plant is ensured by carrying out fracture analysis of the RPV against thermal shock. Carrying out fracture tests on RPV/large scale components is not always feasible. Hence, studies on laboratory level specimens are necessary to validate and supplement the prototype results. This paper aims to study the fracture behaviour of standard Compact Tension [C(T)] specimens, made of RPV steel 20MnMoNi55, subjected to thermal shock through experimental and numerical investigations. Fracture tests have been carried out on the C(T) specimens subjected to thermal transient load and tensile load to quantify the effect of thermal shock. Crack resistance curves are obtained from the fracture tests as per ASTM E1820 and compared with those obtained numerically using XFEM and a good agreement was found. A quantitative study on the crack tip plastic zone, computed using cohesive segment approach, from the numerical analyses justified the experimental crack initiation toughness.