• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.145-152
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• 2010

This study evaluated the fatigue degradation in a SUS316L specimen using the nonlinear ultrasonic method. The nonlinearity of the ultrasonic wave was estimated by a relative nonlinear parameter defined as the ratio of the amplitudes for the fundamental wave to the second harmonic wave. In the experiment, a measurement system with contact transducers was constructed; reliable measurements were assured by keeping measurement conditions consistent and reducing extra harmonics generated in the measurement system. Two types of SUS316L specimen were used in experiments; a rotating bar fatigue specimen and a tensile fatigue specimen. The fatigue condition used was high cycle fatigue. The former specimen had a cylindrical shape and was used to observe the change in the nonlinear parameter after fatigue accumulation in a specimen. The latter was a plate-shaped specimen and was used to confirm the change in the nonlinear parameter at the position where the fatigue stress was concentrated. The measured nonlinear parameter showed a strong correlation to the damage level in both fatigue tests.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.3
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• pp.566-572
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• 2009

This paper has studied breakage possibility of glass insulators by resonance and accelerated deterioration through the comparison of the natural vibration and on site vibration. The natural frequencies of the strut tube glass insulator was measured within a range of less than 1kHz. In the on site vibration, the largest frequency that was imposed on strut tube glass insulators was 80Hz with 1.13g of vertical vibration in the viaduct section, the largest vertical vibration (0.38g) was detected at 103Hz in the open route section. When site vibration and natural vibration of strut tube glass insulators were compared in terms of characteristics, the resonance frequency was not the same. In both the viaduct and open route sections, it seems that the impact by vertical vibration in strut tube glass insulators is large. It's very unlikely that glass insulators were damaged by fatigue accumulation of vibration since the possibility of damage by resonance was very low in consideration of the characteristics of natural vibration and site vibration of glass insulators. In addition, no damage was detected in the accelerated deterioration test.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.5
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• pp.599-606
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• 2022

Strain gauges and the bridge weigh-in-motion (BWIM) method are the representative field measurement methods used for fatigue evaluationsof a steel bridge-in-service. For a fatigue reliability evaluation to assess fatigue damage accumulation, the effective stress range and the number of stress cycles applied as the fatigue details can be estimated based on the AASHTO Manual for Bridge Evaluations with the field measurement data of the target bridge. However, the procedure for estimating the effective stress range and the stress cycles from field measurement data has not been explicitly presented. Furthermore, studies that quantitatively compare differences in fatigue evaluation results according to the field measurement data type or processing method used are still insufficient. Here, a fatigue reliability evaluation is conducted using strain and BWIM data that are measured simultaneously. A frame model and a shell-solid model were generated to examine the effect of the accuracy of the structural analysis model when using BWIM data. Also, two methods of handling BWIM data when estimating the effective stress range and average daily cycles are defined. As a result, differences in evaluation results according to the type of field measurement data used, the accuracy of the structural analysis model, and the data handling method could be quantitatively confirmed.

• Transactions of Materials Processing
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• v.31 no.6
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• pp.384-393
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• 2022

The flow forming process consists of a split process, a divide process, and a forming process. The split process is a forming process in which rollers radially permeate a simple disc-shaped forging material and split it in both directions to form a top-bottom bidirectional cup. It is advantageous for post-processing to deepen the forming depth in the split process but this characteristic causes the failure near the edge of the mandrel during the actual process. The split process was analyzed using Rigid Plastic FEM, and the stress analysis of the mandrel was conducted to find the cause of the failure. It was found that the failure occurred due to fatigue accumulation damage caused by repeated residual stress.

• Journal of Physiology & Pathology in Korean Medicine
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• v.16 no.4
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• pp.684-692
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• 2002

Cordyceps militaris has been known as a Chinese traditional medicine for the treatment of tuberculosis, asthma, kidney disease, debility and fatigue etc. This study was attempted to investigate the therapeutic effect of C. militaris extract on the cytotoxic activity of HepG2, human hepatocellular carcinoma cells and the liver damage induced by carbon tetrachloride in SD rats. C. militaris extracts inhibited significantly the proliferation of HepG2 cells in vitro. Carbon tetrachloride(CCl₄) caused a significant an increase in liver weight, serum aspartate aminotransferase(AST) and alanine aminotransferase(ALT) activity, alkaline phosphatase(ALP), serum thiobarbituric acid reactive substances (TBARS), microsomal TBARS, and decrease in microsomal detoxification enzymes (cytochrome P-450, P-450 reductase, cytochrome b5, b5 reductase). TBARS and ALP in serum pretreated with C. militaris extracts (300mg/kg/day, 600mg/kg/day) was significantly reduced compared to control group(CCl₄). Cytochrome b5 and b5 reductase activities were significantly increased in CM300 (300 mg/kg/day) and CM600 group(600 mg/kg/day), and cytochrome P-450 reductase was significantly increased in CM300 group. Pretreatment (100, 300, and 600 mg/kg/day for 7 days) of C. militaris with CCl₄ was significantly inhibited the accumulation microsomal TBARS and the significantly increased in the cytochrome P-450 activity. These results suggested that C. militaris (300mg/kg/day for 7 days) has appreciable therapeutic effect on CCl₄ induced hepatotoxicity.

• Journal of Life Science
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• v.12 no.2
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• pp.136-143
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• 2002

Jaboyangyeong-hwan (IAE) has been known as a traditional medicine for the treatment of debility, fatigue, and liver diseases. The hepatoprotective effect of the water extract of Jaboyangyeong-hwan was investigated against carbon tetrachloride ($CCl_4$)-induced hepatic damage. A single intraperitoneal injection of $CCl_4$produced liver damage in rats as manifested by the significant rise of aspartate aminotransferase (AST, alanine aminotransferase (ALT), and alkaline phosphatase (ALP) in serum as compared to those of untreated normal group. Pretreatments of rats with the JAE extract (300, 600, and 1200 mg/kg for 7 days) were significantly reduced AST, ALT, and ALP levels compared with $CCl_4$-treated control group. Treatment of rats with $CCl_4$led to significantly increase in lipid peroxidation and significantly decrease in cytochrome P450 and P450 reductase. The oral administration of the JAE extract significantly inhibited the accumulation of microsomal thiobarbituric acid reactive substance (TBARS) and increased the cytochrome P450 and P450 reductase activity. All these biochemical alterations resulting from $CCl_4$administration were inhibited by the pretreatment with JAE extract. These results suggest that JAE water extract can be useful as a hepatoprotective agent.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.4
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• pp.537-548
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• 2022

It is important to design the pavement thickness considering heavy-duty traffic loads, which can cause excessive stress and strain in the pavement. Port-rear roads and industrial roads have many problems due to early stress in pavement because these have a higher ratio of heavy loads than general roads such as national roads and expressways. Internationally, composite pavement has been widely applied in pavement designs in heavy-duty areas. Composite pavement is established as an economic pavement type that can increase the design life by nearly double compared to that of existing pavement while also decreasing maintenance and user costs. This study suggests a thickness design method for composite pavement using roller-compacted concrete as a base material to ensure long-term serviceability in heavy-duty areas such as port-rear roads and industrial roads. A three-dimensional finite element analysis was conducted to investigate the mechanical behavior and the long-term pavement performance ultimately to suggest a thickness design method that considers changes in the material properties of the roller-compacted concrete (RCC) base layer. In addition, this study presents a user-friendly catalog design method for RCC-base composite pavement considering the concept of linear damage accumulation for each container trailer depending on the season.