• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.39-39
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• 2000

축류 압축기 블레이드(blade)와 베인(vane)이 정하중(static load)에서 충분한 강도를 지니고 있더라도 반복하중이나 교번하중을 받게되면, 그 하중이 작더라도 파괴가 일어날 수 있다. 축류 압축기 블레이드와 베인의 피로파괴(fatigue failure) 현상은 개발 중인 가스터빈엔진 뿐만 아니라 현재 운용중인 엔진에서도 발생할 수 있는 엔진손상의 주요 원인이다. 블레이드나 베인의 동적 안정성 평가는 에어포일(airfoil)의 피로특성과 엔진운용조건에 따라서 발생하는 복잡한 공력가진과의 연관성을 고려하여 수행되어야 하기 때문에, 해석과 구성품 시험을 통하여 우선적으로 강도 평가를 실시하여야 한다.(중략)

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2001.11a
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• pp.219-224
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• 2001

본 연구는 울진 원자력발전소 5＆6호기 Class 1680, Parallel Gate 16-inch, Motor Operated Valve (Valve ID No. SI-653 and 654)에 부착되는 Equalizing Bypass Pipe Line (EBPL)이 밸브 시스템에 발생시키는 진동하중에 의한 영향을 동적 피로안정성 관점에서 규명하기 위하여 수행된 것이다. Equalizing Bypass Line Part의 최종 설계된 형상을 Fig. 1에 나타내었다. 본 해석을 위하여 운용 중 발생되는 부착부의 잔류진동 레벨이 3축 방향 가속도로 측정되었다. 본 연구에서는 해당 시변 가속도 데이터를 바탕으로 정확한 시간-응력 이력을 얻기 위하여 시간영역에서 천이 진동해석 (Transient Vibration Analysis)을 수행하였으며, 이를 실제적인 피로해석에 활용하였다. 시간영역에서의 천이 진동해석 및 피로해석을 위해 상용유한요소 해석프로그램인 ANSYS (Version 5.6)를 활용하였다.(중략)

• The tire
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• s.116
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• pp.22-30
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• 1985

전년 9~10월호에서는 케블라의 종류,용도, 경제성,미세구조, 제법, 내열성 ,치수안전성 등에 대해 설명하였으나, 이번 호에서는 습ㆍ건열열화, 피로성, 동적점탄성 등에 대해서 살펴보고자 한다.

• Restorative Dentistry and Endodontics
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• v.31 no.2
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• pp.96-102
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• 2006

There are various factors affecting the fracture of NiTi rotary files. This study was performed to evaluate the effect of cross sectional area, pecking motion and pecking distance on the cyclic fatigue fracture of different NiTi files. Five different NiTi $files-Profile^{(R)}$ (Maillefer, Ballaigue, Switzerland), $ProTaper^{TM}$(Maillefer, Ballaigue, Switzerland), $K3^{(R)}$ (SybronEndo. Orange, CA) , Hero $642^{(R)}$ (Micro-mega, Besancon, France), Hero $Shaper^{(R)}$ (Micro-mega, Besancon, France)-were used. Each file was embedded in temporary resin, sectioned horizontally and observed with scanning electron microscope. The ratio of cross-sectional area to the circumscribed circle was calculated. Special device was fabricated to simulate the cyclic fatigue fracture of NiTi file in the curved canal,. On this device, NiTi files were rotated (300rpm) with different pecking distances (3 mm or 6 mm) and with different motions (static motion or dynamic pecking motion) . Time until fracture occurs was measured. The results demonstrated that cross-sectional area didn't have any effect on the time of file fracture. Among the files, $Profile^{(R)}$ took the longest time to be fractured. Between the pecking motions, dynamic motion took the longer time to be fractured than static motion. There was no significant difference between the pecking distances with dynamic motion, however with static motion, the longer time was taken at 3mm distance. In this study, we could suggest that dynamic pecking motion would lengthen the time for NiTi file to be fractured from cyclic fatigue.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1669-1674
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• 2012

A commonly analytical estimation of fatigue life on rubber components is using fatigue life equation based on various fatigue test results. However, such method has very restricted applicability in actual designing processes because performing fatigue tests requires a lot of time and money. In addition, non-standard rubber materials and their randomness make it hard to make databases. In this paper, the other fatigue life estimation method using tearing energy was suggested. We performed static and dynamic tearing test about automotive vibration rubber materials and a finite element formulation using a virtual crack to calculate the tearing energy of rubber components with complicated shapes. To using the suggested method, fatigue life of an automotive motor mount has been estimated and verified the reliability of this method by using comparison between the estimated values and the actual fatigue life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1213-1219
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• 2012

A remote $CO_2$ laser system can rapidly change both the distance and the direction of the laser beam by moving a lens and rotating mirrors. It is then easy to weld complex patterns of weld lines. A conventional spot weld joint specimen and a remote $CO_2$ laser weld joint specimen with complex weld line patterns were prepared and tested both statically and dynamically. The relationships between the fatigue strength, i. e. the maximum cyclic force, and the fatigue life were obtained. The fatigue strength of the tested welded joints at two million cycles was found to be approximately 10% of the static strength. Furthermore, it was observed that the fatigue fracture mode changed with the level of the applied cyclic force. The fatigue crack origins were confirmed as the highest stress points found in the structural analysis. The maximum cyclic stress for different weld patterns converges as the fatigue life approaches two million cycles.

• The Korean Journal of Nuclear Medicine Technology
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• v.19 no.2
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• pp.81-86
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• 2015

Purpose This study was to evaluate the usefulness through the comparison of patients group and healthy control group by acquiring a variety of functional parameters index from time-activity curves of salivary gland scintigraphy using $^{99m}Tc$. Materials and Methods From December 2014 to February 2015 with the targets of 30 patients in the patient group who presented themselves with xerostomia and underwent the salivary gland scan and 10 people in healthy control group, approximately 30 minutes of dynamic Scan was carried out after the intravenous bolus injection of 370 MBq of $^{99m}TcO_4{^-}$ and per os stimulation with Vitamin C powder 20 minutes after the injection. The method of quantitative analysis was as follows, the time-activity curve was drawn after the parotid gland and submandible gland were prescribed as a region of interest, a variety of functional parameters index was obtained in each position of the curve, and the patients group and the control group were compared. Results As for the methods applied in comparison and measurement, uptake ratio (UR), time at maximum counts (Tmax), time at minimum counts (Tmin), maximum accumulation (MA), accumulation velocity, maximum secretion (MS), maximum stimulation secretion (MSS), and secretion velocity (SV) were used. In the comparison of functional parameters index of patient group and normal group, the healthy normal group showed significant difference compared to the patient group in all indices except for the minimum radioactivity time (Tmin), and also in terms of variation over time the normal group showed significant difference compared to the patient group (p<0.05). Conclusion Consequently, it was considered that the quantitative analysis that used a variety of functional parameters index would be useful for evaluating the function of the salivary glands of the patients with xerostomia as an objective and standardized information.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.819-829
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• 2008

Fatigue cracking occurs over long time period because dynamic strength of slab continuously decreases by vehicle loading repetitively applied to the concrete pavement. To more accurately predict the fatigue life of the concrete pavement, the stress due to environmental loading should be considered prior to calculating the stress due to the vehicle loading because the stress due to temperature and moisture distribution always exists within the slab. Accordingly, a new fatigue model considering the environmental loading was developed in this research by evaluating factors of existing fatigue models most widely used and by making data points from the models. The applicability of the new model was evaluated by performing a fatigue analysis on the general concrete pavement structure using local climatic and traffic conditions in Korea. It was concluded that the top-down cracking due to the tensile stress at top of the slab is dominant cause of the fatigue failure than the bottom-up cracking occurred at bottom of the slab. More advanced fatigue analysis considering vehicle speed is expected by developing this study.

• Journal of the KSME
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• v.28 no.4
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• pp.328-336
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• 1988

파괴인성은 내적 및 외적요인 등에 의해 변할 뿐만 아니라 조직의 불균질성 때문에 소성둔화 및 파괴가 균일하게 일어나지 않으므로 이에 대응한 파괴인성을 선택하여 평가함이 가장 중요하다. 또한 기계의 고속화에 따라 충격적인 하중에 의한 동적파괴의 문제가 중요하게 되고 이에 따라 동적파괴인성 평가법의 확립에도 많은 연구가 필요하다. 한편 피로균열진전거동의 실험에는 많은 시간과 인적 노력이 필요로 하며 이러한 문제점을 해결하여 균열진전 측정의 정밀화 및 효율성을 높이기 위해서는 컴퓨터의 이점을 적극적으로 응용할 필요가 있다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.186-186
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• 2010

개별 블레이드 피치 제어(individual blade pitch control)는 각각의 로터 블레이드의 피치각을 독립적으로 조정함으로써 블레이드에 작용하는 공력을 변화시키는 원리로 풍력 터빈 구조물에 발생하는 동적 피로하중을 저감시키기 위한 제어기법이다. 그러나 개별 피치 제어에 의해 발생하는 각 블레이드의 독립적인 피치 운동은 풍력 터빈 회전자에 비대칭성을 야기하고 구조물의 동적 불안정 현상을 발생시킬 수 있기 때문에 이에 대한 정확한 동적 해석이 선행되어야 한다. 하지만 블레이드의 피치 운동이 반영된 풍력 터빈은 시변계로 간주되어 기존의 시불변계 해석기법을 직접 적용할 수 없기 때문에 동적 해석에 어려움이 있다. 이 논문에서는 각각의 블레이드 피치운동을 주기함수로 근사화 함으로써 풍력 터빈을 주기 시변계로 모형화한다. 그리고 효율적으로 주기 시변계의 근사해를 구하기 위한 변조 좌표 변환(modulated coordinate transformation)기법을 적용하여 블레이드의 피치운동이 반영된 풍력 터빈의 동적 안정성 해석을 수행하였다. 그리고 현재 풍력 터빈의 동적 해석에 활용되는 대표적인 해석 기법인 다중 블레이드 좌표변환(multi-blade coordinate transformation)기법을 이용한 해석보다 정확한 결과를 얻을 수 있음을 보였다.