• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.4
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• pp.160-167
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• 2012

This paper is concerned with a particular fracture mechanics parameter ${\Delta}K_{th}$, known as the 'threshold stress intensity range', or 'fatigue threshold'. This threshold ${\Delta}K_{th}$ constitutes, as it were, a hinge between the notion of crack initiation and the notion of crack growth. It has often been thought that, like the endurance limit, it could be an intrinsic criterion of the material. The study was conducted on a SA-508 pressure vessel steel used in the nuclear power industry. This material exhibits a typical threshold effect in the range of the crack growth rates which were determined; that is, below approximately $da/dN=10^{-6}mm/cycle$, the slope of the da./dN versus ${\Delta}K$ curve is almost vertical. The value of ${\Delta}K_{th}$ was determined at a growth rate of $10^{-7}$ mm/cycle according to the ASTM Standard for threshold testing. The fatigue threshold values are in the range 21 $kg/mm^{3/2}$ to 12 $kg/mm^{3/2}$ depending on the stress ratio effect.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3
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• pp.414-420
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• 2013

Research on decreasing the weight of composite sandwich panels is in progress. This paper reports the experimental results for the mechanical behavior of a composite sandwich panel. The skins of sandwich panels were made of glass fiber sheets and plywood matrix composites. Their interior layers consisted of glass fiber pultrusion pipes and gold foam. Experimental tests were performed to obtain the mechanical properties and complex mechanical behavior. Before fatigue tests, tensile tests and 3-point bending tests were carried out to obtain the optimal design and determine their strength and failure mechanisms in the flat-wise position. After the static test, a fatigue test were conducted at a load frequency of 5 Hz, stress ratio (R) of 0.1, and endurance limit for the S-N curve. It showed that the failure modes were related to both the core design and skin failure.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.2
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• pp.145-151
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• 2014

Recently, the growing demand for weight reduction and improved structure durabilityfor commercial vehicles has led to active research into the development and application of suitablecomposite materials. This studysuggests abimaterial composite frame produced by apultrusion process to replace steel frames. We focused on the development of a composite frameconsisting of two types of materialsby mixing anorthotropic material with anisotropic material. The inside layer consisted of an aluminum pipe, and the outside layer was composed of a glass fiber pipe. To determine the strength and failure mechanisms of the composite material, tensile tests, shear tests, and three-point bending tests were conducted, followed by fatigue tests. After static testing, the fatigue tests were conducted at a load frequency of 5 Hz, a stress ratio (R) of 0.1, and an endurance limit of $10^6$ for the S-N curve. The resultsshowed that the failure modes were related to both the core design and the laminating conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1320-1329
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• 1990

A static performance tester for a torque rod assembly was developed to evaluate the three characteristics of the rod rubber bushing : radial spring characteristic, thrust spring characteristic, and rotational torque characteristic. Among the various schemes considered in the conceptual design stage, the final versatile type was determined to perform three different tests in one machine. The performance testing machine carried out radial spring test, thrust spring test, and torque test of the torque rod assembly. Static performance of the torque rod assembly was evaluated with the tester developed and fatigue strength of the assembly was also tested with the servo-hydraulic structural fatigue testing machine. The life of the component was found to be related with the rubber quality and adhesionability between the rubber and the steel rod. The optimum rubber hardness was experimentally found by changing the chemical compositions of rubber, and the adhesion was improved by optimizing the shape of the outer section of a the rubber, this study ensured the development of a reliable torque rod assembly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.913-920
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• 2011

We describe the evaluation of the fatigue life and strength of a lightweight railway bogie frame made of glass fiber/epoxy 4-harness satin-woven composites. To obtain the S-N curve for the evaluation of the fatigue characteristics of the composite bogie frame, we performed a tension-compression fatigue test for composite specimens with different stacking sequences of the warp direction, fill direction, and $0^{\circ}/90^^{\circ}$ direction. We used a stress ratio (R) of -1, a frequency of 5 Hz, and an endurance limit of $10^7$. The fatigue strength of the composite bogie frame was evaluated by a Goodman diagram according to JIS E 4207. The results show that the fatigue life and strength of the lightweight composite bogie satisfy the requirements of JIS E 4207. Given its weight, its performance was better than that of a conventional metal bogie frame based on an SM490A steel material.

• The Korean Journal of Food And Nutrition
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• v.33 no.4
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• pp.363-371
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• 2020

This study was designed to evaluate the improvement in exercise endurance by Hovenia dulcis fruit hot water extract (HDWE) for the potential application as a functional food material. The effect was based on the evaluation of the forced-swimming capacity and changes in biochemical parameters in mice. Six-week-old mice were classified into four groups based on a randomized block design: the negative control group, the HDWE 50 mg/kg body weight group, the HDWE 200 mg/kg body weight group, and the 1-octacosanol 50 mg/kg body weight group (n=8 mice per group). The swimming exercise time in the HDWE-50 group was increased at 545±43 sec compared to the control group at 263±28 sec. The HDWE-200 fatigue indicators, lactate acid and ammonia content, decreased to 4.99±0.33 mg/mL and 0.63±0.05 mg/mL, respectively. In addition, the content of glycogen in the liver and muscle tended to increase in the group administered HDWE but was not significant. Likewise, the LDH and glucose contents were increased compared to the control group. The muscle damage indicators ALT (52.7±2.6 U/L) and AST (42.5±5.2 U/L) tended to decrease compared to the control group (76.4±10.2 U/L).

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.939-950
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• 2011

In this study, the load test of rubber tire bogie for monorail type LRT. Bogie for rolling stock in safety operation of the vehicle as an essential core unit before applying to the vehicle safety and reliability should be tested sufficiently. Rubber tire monorail type bogie compared to the traditional bogie wheel lots of formats, the complexity of the load acting static load test, the bogie of the vehicle operation conditions by structural analysis by considering the loading conditions was evaluated by calculating. Test methods and evaluation criteria based on urban rail vehicle performance testing by applying the test were welded parts and materials for the results leading to material fatigue endurance test by applying the result of evaluating the structure has been identified as safe.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.9
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• pp.777-782
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• 2014

Usually, railway axles are designed for infinite life based on endurance limit of the material and the axle is not fractured immediately when a surface crack initiated. The railway axles have been inspected regularly by NDT such as ultrasonic testing, magnetic testing and eddy current testing and so on. Because the axle failure is profoundly influenced by the probability of missing a fatigue crack during an NDT inspection, it is necessary to evaluate the Non Destructive Interval of railway axle. In the present paper, the Non Destructive Interval of railway axle based on fracture mechanics and finite element analysis was investigated. It was shown that the Non Destructive Interval of railway axle can be evaluated using fracture mechanics approach and extended using NDT which a crack can detect clearly.

• Journal of the Korean Society of Safety
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• v.21 no.2 s.74
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• pp.15-21
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• 2006

The railroad bogie's components experience repeated loading during service. Especially, oil damper bush has been fatigue fractured on the plane between rubber and steel stem during service, and which results in inferior of performance of the bogie. In this study, in order to offer a proper maintenance method of the bush, bubber bush used for the oil damper was fatigue tested and its damage fraction during service was estimated. Also, FEM analysis on the bush was conducted. When 1400, 1200, and 1000kgf of repeated loads were applied to the oil damper bush, final damage fraction exhibited 63.7%, 50% and 40%. From the results of FEM analysis, deformation energy density was found to be $0.5452kgf/mm^{2}$ at an applied load of 1400kgf and the location with maximum value coincided with the fractured location of the bush. Finally, it will be desirable to adopt the normalized damage fraction rather than absolute damage fraction in estimating remaining service lifetime of the bush.

• Journal of muscle and joint health
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• v.7 no.1
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• pp.102-130
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• 2000

The aims of this study were to understand and to predict the determinant factors affecting the exercise behaviors and physical fitness by testing the Ponder's health promotion model, and to help the patients with rheumatoid arthritis and osteoarthritis perform the continuous exercise program, and to help them maximize the physical effect such as muscle strength. endurance, and fuctional status and mental effects including self efficacy and quality of life, and improve the physical and mental wellbeing, and to provide a basis for the nursing intervention strategies. We analyzed the clinical records of 208 patients with rheumatoid arthritis and degenerative arthritis who visited the outpatient clinics at H university hospital in Seoul between October 5, 1999 and October 24, 1999. Data were composed of self reported questionnaire and good of fitness score which were obtained by pedalling the ergometer of bicycle for 9 minutes. SPSS Win 8.0 and Window LISREL 8.12a were used for statistical analysis. 24 Of 54 hypothetical paths were supported in modified model, which was considered as a proper model with improved fit index. The physical fitness was directly influenced by exercise participation behavior and education level, and indirectly by physical fitness, while fatigue, physical disability, pastexercise behavior, life-style, self-efficacy, which explained 20% of physical fitness. The exercise participation were directly influenced by perceived benefits and self-efficacy, and indirectly influenced by life-style, fatigue and physical disability, and directly and indirectly by past exercise behavior, which explained 53% of exercise participation. Exercise score were directly affected by perceived health status, perceived benefits, self efficacy, and past exercise behavior, and were indirectly affected by fatigue, physical disability, and life-style, which explained 50%. Perceived health status were directly influeced by level of education, depression, sleep disorder, and physical disability, which explained 34% of perceived health status. Perceived benefit was directly influenced by fatigue, sleep disorder, physical disability, and life-style, which explained 45%. Perceived barriers was directly influenced by fatigue, sleep disorder, and lifestyle, which explained 9%. Self- efficacy was directly influenced by fatigue, physical disability, past exercise behavior, and level of education, which explained 61%. In conclusion, important variables for physical fitness were exercise participation and level of education, and variables affecting exercise participation were perceived self-efficacy, benefits, and past exercise behavior. Perceived self-efficacy of exercise was a significant predictor of exercise participation. Life-style, fatigue, and physical disability showed direct effects on perceived benefit, perceived barriers, and self-efficacy, and indirect effects on exercise behavior. Therefore, disease related factor should be minimized for physical performance and well being in nursing intervention for patients with rheumatoid arthritis, and plans to promote and continue exercise should be soaked to reduce disability. In addition, Exercise program should be planned and performed by the exact evaluation of exercise according to the ability of the patients and the contents to improve the importance of exercise and self efficacy in self control program, dedicated educational program should be involved.