• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.850-856
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• 1998

The dynaamic fatigue behavior of alumina ceramics was observed at room temperature using four-point bending method. Dynamic fatigue fracture strength was observed as function of down speed and notch length. The crack growth exponent of the specimens was calculated from the fracture strength and lifetime in dynamic fatigue test. After loading the stresses in the range of 0% to 105% compared with the average in-ert strength the value of residual fracture strength was measured for unnotched and 0.5mm notched speci-mens at the 0.001 and 0.0005 mm/min down speed respectively. After the 95% stress of the average inert strength was applied repeatedly the value of rsidual fracture strength was measured for 0.5mm notched specimens at the 0.001 and 0.0005 mm/min down speed respectively. The material constant A was found to be almost the same and not to depend on the loading mode or the down speed for unnotched and notched specimen. The value of fracture strength with time calculated from the constants n and A was in good agreement with the measured value.

• Journal of the Korean Society for Railway
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• v.7 no.1
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• pp.32-36
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• 2004

Aluminum carbody for rolling stocks is light and perfectly recycled, but includes severe defects which are very dangerous to fatigue strength. Static load test has been performed up to date to assess structural safety of the carbody. However, static load test is not sufficient to evaluate fatigue strength of the carbody, because fatigue failure is caused by dynamic load. In this study, the established load test methods for carbody are described and the characteristics of the methods are discussed. Also, a testing method to simulate dynamic loading condition is proposed for evaluation of fatigue strength of the carbody. The results by the proposed testing method are compared with the results by the static load test and new findings are discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.191-198
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• 2000

Dynamic fatigue test is carried out using soil model box for the evaluation of performance of three different roadbed materials. Bearing capacity, settlement and mud pumping phenomenon of each roadbed materials as well as penetration of model ballast into the roadbeds are investigated. It was found that settlement of slag and crushed stone roadbed is smaller than the soil roadbed during dynamic fatigue test with same initial conditions.

• 연구논문집
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• s.27
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• pp.47-55
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• 1997

Fatigue life prediction of mechanical components is necessary to develop new products, which is very expensive and time-consuming. This paper reviews technologies proposed for computation of dynamic stress in mechanical components. The methods based on multibody dynamics are considering more real operational conditions than other methods. The technology for fatigue life prediction without the prototype for experiment results in cost and time saving. This technology can be applied to design of various mechanical components like carbody.

• Journal of Applied Reliability
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• v.17 no.1
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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.

• The Journal of Korean Physical Therapy
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• v.27 no.4
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• pp.207-213
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• 2015

Purpose: The aim of the current study was to investigate EMG activity on dynamic balance of subjects with functional lumbar instability following fatigue of low back. Methods: The subjects (24 university students) were divided into 2 groups; functional lumbar instability group (6 males and 6 females) and lumbar stable group (7 males and 5 females) who could complete a questionnaire and undergo a prone instability test. All participants were evaluated for distribution of muscle activity using the TeleMyo DTSTM system. Dynamic balance was tested by Y balance test. This study was conducted for measurement of EMG activity on dynamic balance with the difference between FLIG and control group following muscle fatigue. Results: The functional lumbar instability group (FLIG) showed a significantly lower YBT score (%) of anterior, posterolateral direction on Y-balance test (YBT) in dynamic balance than the lumbar stable group (LSG) (p<0.05). The FLIG was significantly lower than the LSG in anterior direction in EMG activity(%) of MF, RA, ES, GMX, GME, RF, and posteromedial direction in EMG activity(%) of IO, ES and then posterolateral direction in EMG activity(%) of IO, ES in dynamic balance (p<0.05). There was significant correlation of MF, RA, and GMX in anterior reach direction (p<0.05) and ES, GME (p<0.01) and IO, ES in posteromedial reach direction (p<0.05) and EO, ES, GMX in posterolateral reach direction (p<0.05) there was positive correlation. Conclusion: This study showed that FLIG effected EMG activity by dynamic balance following muscle fatigue. Further study is needed for measurement of various ages and work with lumbar instability for clinical application.

• Structural Engineering and Mechanics
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• v.49 no.2
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• pp.237-259
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• 2014

Wind-induced failure around screwed connections has been documented in roof and wall cladding systems made with steel sheet cold-formed panels during high wind events. Previous research has found that low cycle fatigue caused by stress concentration and fluctuating wind loads is responsible for most such failures. A dynamic load protocol was employed in this work to represent fatigue under wind effects. A finite element model and fatigue criteria were implemented and compared with laboratory experiments in order to predict the fatigue failure associated with fluctuating wind loads. Results are used to develop an analytical model which can be employed for the fatigue analysis of steel cold-formed cladding systems. Existing three dimensional fatigue criteria are implemented and correlated with fatigue damage observed on steel claddings. Parametric studies are used to formulate suitable yet simple fatigue criteria. Fatigue failure is predicted in different configurations of loads, types of connections, and thicknesses of steel folded plate cladding. The analytical model, which correlated with experimental results reported in a companion paper, was validated for the fatigue life prediction and failure mechanism of different connection types and thicknesses of cold-formed steel cladding.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.844-848
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• 2004

We evaluate the durability of vehicle chassis component under dynamic loadings. Since the fatigue analysis of vehicle component is based on the dynamic load history it must be done by dynamic analysis. But in case the vehicle component has natural frequencies much larger than reversing frequencies of load history, we can get small analysis errors by applying quasi-static analysis. So it is inefficient that we apply to the dynamic analysis for all the vehicle components. In this research, we discuss the quasi-static analysis method which is appropriate for the fatigue analysis. And in case we can only perform the fatigue analysis based on dynamic analysis, we introduce more efficient method in the analysis time and hard disk storage.

• International Journal of Automotive Technology
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• v.5 no.3
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• pp.215-219
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• 2004

A vehicle structure needs to be more precisely analyzed because of complexities and varieties. Structural fatigue which is generated by fluctuations of stresses during the service life of a mechanical system is the primary concern in the structural design for safety. A fatigue life is difficult to obtain in structural components during the service life of mechanical systems since the fluctuating stress contributes to fatigue. This study introduces new procedures to measure the lethargy coefficient and to predict the fatigue life of a mechanical structure by using molecular dynamic simulation. A lethargy coefficient is the total defect-estimating coefficient, which was obtained by using the results of a simple tensile test in this study. With this lethargy coefficient, fatigue life was estimated. The proposed method will be useful in predicting the fatigue life of a structurally-modified vehicle design. The effectiveness of the proposed method using lethargy coefficient measurement to predict the fatigue life of a structure was examined by applying this method to predict the fatigue life of SS41 steel, used extensively as material of vehicle structures. Two types of specimen such as pre-cracked plate and simple plate is discussed. equation of fatigue life using the lethargy coefficient and failure time, both obtained from a simple tensile test, will be useful in engineering. This measurement and prediction technology will be extended for use in analysis of any geometric shapes of modified automotive structures.

• The Journal of Korean Physical Therapy
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• v.29 no.1
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• pp.39-43
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• 2017

Purpose: This study was to investigate the effects of unilateral muscle fatigue in knee and ankle joints on balance and gait in healthy adults. Methods: Exercise inducing muscle fatigue in the knee joint consisted of concentric and eccentric contraction of dominant knee extensors in healthy adults by using the Leg Extension Rehap exercise machine (HUR, Finland). Exercise inducing muscle fatigue in the ankle joint was composed of voluntary contractions and forced contractions of the dominant plantar flexors in healthy adults. Exercises to induce muscle fatigue in the knee and ankle joints were performed until the subject complained of fatigue or pain, the occurrence of muscle fatigue was confirmed by electromyography. We measured static and dynamic balance using the Good Balance system and gait performance by RS-scan. Results: Static and dynamic balance ability and spatial-temporal gait decreased significantly after muscle fatigue in knee and ankle joint. Conclusion: These results show that unilateral muscle fatigue of the lower extremities affected postural control and gait. Therefore, therapists and sport trainers should minimize the risks of fall and injuries related to unilateral muscle fatigue.