• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.425-433
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• 2001

A correlation between fatigue damage and acousto-ultrasonic (AU) parameters has been obtained from signals acquired during fatigue loading of the single-lap joints of a carbon-fiber reinforced plastic (CFRP) laminates and A16061 plate. The correlation showed an analogy to those representing the stiffness reduction $(E/E_0)$ of polymer matrix composites by the accumulation of fatigue damage. This has been attributed to the transmission characteristics of acoustic wave energy through bonded joints with delamination-type defects and their influence on the change of spectral content of AU signals. Another correlation between fatigue cycles and the spectral magnitude of acoustic emission (AE) signals has also been found during the final stage of fatigue loading. Both AU and AE can be applied almost in real-time to monitor the evolution of damage during fatigue loading.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.3
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• pp.126-134
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• 1995

The crack initiation life evaluation which is the most commonly used approach in fatigue strength studies for the designers, is performed for the crankshaft of mid-size engine. In order to evaluate the fatigue strength, structural analysis model and applied loads on crankshaft are prepared based on the cyclic system. Using the response data of the finite element analysis, crack initiation life is predicted and plotted on crankshaft geometric model. In this analysis, general purpose programs such as PATRAN, NASTRAN and EMRC/NISA are actively utilized. Life distribution contour plots, which is not yet established as an active tool in actual design system of ship structure & components, are suggested and examples for active predicting procedure such as stress contour plotting in structure strength analysis, are illustrated. Additionally, several correlated equations for prediction of the crack initiation life are introduced and discussed to improve the fatigue strength prediction of crankshaft.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.111-122
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• 2000

In this study, A series of fatigue tests have been performed on the fillet welded joints of cover plates in steel plate girders in order to quantitatively assess the fatigue characteristics according to the shapes of cover plates. From the results of fatigue tests, it has been shown that the fatigue strengths were slightly different according to their shapes, but satisfied the fatigue design curves in Korea and other countries. Also, from the results of beachmark tests, it has been confirmed that the points of fatigue crack initiation were closely related to the shapes of weld bead toes, and fatigue cracks simultaneously initiated from several points in weld bead toes have been grown as semi-elliptical surface cracks, and these cracks have been coalesced each other, and grown as through thickness cracks, and finally reached to fracture. Besides, from the results of fracture mechanics approaches, stress gradient factors were the most dominant factors among crack correction factors obtained from the existing equations and finite element analysis, and the fatigue life on fillet welded joints of cover plates could be estimated using the relations between fatigue crack growth rate and stress intensity factor range obtained from finite element analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.4
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• pp.286-291
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• 2004

There are fatigue fractures at the practical area. The fatigue load happens non- constantly. As it is impossible to be predicted, it can not be known when the fracture happens. Non -constant fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by the program of Ansys workbench. These results are greatly applied as the practical structures to predict the prevention of failure and the endurance.

• Proceedings of the KAIS Fall Conference
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• 2004.06a
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• pp.100-102
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• 2004

There are fatigue fractures at the practical area. The fatigue load happens non- constantly. As it is impossible to be predicted, it can not be known when the fracture happens. Non -constant fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by the program of Ansys workbench. These results are greatly applied as the Practical structures to Predict the prevention of failure and the endurance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4398-4404
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• 2015

Stainless steel sheets are widely used as the structural material for dynamic machine structures, These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding, For fatigue design of gas welded joints such as various type joint. It is necessary to obtain design information on stress distribution at the weldment as well as fatigue strength of gas welded joints. Thus in this paper, ${\Delta}P-N_f$ curves were obtained by fatigue tests. and, ${\Delta}P-N_f$ curves were rearranged in the ${\Delta}{\sigma}-N_f$ relation with the hot spot stresses at the gas welded joints. Using these results, the accelerated life test(ALT) is conducted. From the experiment results, an life prediction model is derived and factors are estimated. So it is intended to obtain the useful information for the fatigue lifetime of welded joints and data analysis by statistic reliability method, to save time and cost, and to develop optimum accelerated life prediction plans.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.35.2-35.2
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• 2009

최근 전세계적으로 저탄소, 녹색성장으로 인하여 원자력발전이 주목받고 있다. 또한 에너지의 고효율로 인한 발전소의 설비가 대형화가 됨에 따라 발전소의 수명평가와 건전성평가가 중요해지고 있다. 일반적으로 구조물 내에 존재하는 균열의 크기와 형상을 파악하여 피로균열전파속도를 평가함으로써 건전성평가를 확인하고 있다. 그리고 고온, 고압에서의 피로균열전파속도는직류전위차 (Direct Current Potential Drop : DCPD)법을 사용하고 있다. DCPD법은 균열의 정밀한 측정방법으로써 측정시 오차가 발생하기 때문에 ASTM에서 제시된 incremental polynomial 법을 권고하고 있다. 따라서 본 연구에서는 피로균열전파전파속도의통계적처리를 통해서 합리적인 곡선을 구하여 건전성평가에 활용하고자 한다. 실험에 사용된 시편은 두께 5mm, 폭 25.4mm CT시편을 사용하였으며, 1mm의 예비균열을 주었다. 그리고 실험온도는 상온에서 실시 하였으며, 주파수는 10Hz를 주었다. 그리고 DCPD 측정을 위해 5A의 전류를 주었으며, 이때 측정된 전압값을 ASTM에 제시된 관계식에넣어 균열길이로 환산하였으며, 데이터처리는 ASTM에 제시된 incremental polynomial법을 기본적으로 사용하였다. 또한 ASTM에 제시된 2n+1을 이용하여 데이터의 수 n을 1~7 까지 변화를 주어 3~15 point 까지 데이터를 처리하여곡선을 제시하였다. 분석결과 $R^2$값이 1을 기준으로 했을 때 3~7 point 까지는큰 차이를 보이지 않았지만 9-point 이후부터는 $R^2$ 감소함을 알 수 있었다. 또한 적용된 데이터의수에 따라 피로군열전파속도 곡선에서 측정된 Paris law의 n값과 C 값은 큰차이를 보이지 않았다.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.701-713
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• 2000

In this study, the 4-point bending test been performed in order to estimate effect of grinding on fatigue characteristics quantitatively for as-welded specimen, grinding specimen & TIG-dressing specimen for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength at $2{\times}106$cycles of grinding specimen and TIG-dressing specimen has been increased compared with as-welded specimen and satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC. As a result of beachmark test, fatigue cracks on all specimens have occurred at several points where stress

• Journal of Korean Society of Steel Construction
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• v.13 no.2
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• pp.211-221
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• 2001

The dynamic force estimation and strength design of KALES(Korea Accelerated Loading and Environmental Simulator) are studied. The KALES is continuously rotating the test track and subjected to the dynamic or impact forces during operation since the track is composed of straight and curved line. To estimate the dynamic equation for the model car which was already made is derived with analytical and experimental techniques. Using similarity relationships between the model car and KALES, the dynamic force and stability properties for KALES can be predicted. The stress analysis and fatigue life estimation of KALES is also estimated with the calculated dynamic load. From the stress analysis and fatigue life estimation results, it was found that the design of KALES is safe.

• Journal of Korean Society of Steel Construction
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• v.29 no.3
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• pp.193-204
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• 2017

Fatigue strength of temporary steels and painted structural steels corroded under outdoor atmospheric environments is not clear. In this study, fatigue tests were carried out on steel plates which were cut off from 7-year-old temporary structural member under subway construction environment and from 75-year-old Yeongdo bridge member under marine atmospheric environment. After removing corrosion production on the steel surface, 3-dimensional surface geometry of the corroded steel was measured at intervals of $1.0{\times}1.0mm$, and corrosion characteristics such as minimum, maximum and mean values of residual thicknesses were calculated. From the fatigue test and FEM analysis results, the relationship between corrosion characteristics and fatigue behavior was presented, and change in fatigue strength of the unpainted and painted steels corroded in outdoor environments was also presented.