• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.467-469
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• 2009

In this study, fatigue samples were prepared from cylinder head parts that are actually used in domestic (A) and foreign (B) automobiles; high-temperature, high-cycle, and low-cycle fatigue characteristics were then evaluated and compared. A study on the correlation between the microstructural factor and high temperature fatigue characteristic was attempted. The chemical compositions of the heat resistant aluminum alloys above represented A356 (A) and A319 (B), respectively. The result of the tensile strength test on material B at $250^{\circ}C$ was higher by 30.8MPa compared to material A. On the other hand, elongation was 8.5% higher for material A. At $130{\circ}C$, material B exhibited high fatigue life given high cycle fatigue under high stress, whereas material A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility is increased, material A demonstrated higher fatigue life. Through the observation of the differences in microstructure and the fatigue fracture surface, an attempt to explain the high-temperature fatigue deformation behavior of the materials was made.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.17-21
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• 1997

The fatigue crack propagation rate has so far been measured by the effective stress intensity factor range Δ K/sub eff/. But no research has been done to study how much the crack opening ratio influences the expectation of the fatigue crack propagation. Therefore, this paper evaluates of the crack opening ratio on the fatigue crack propagation life by using the method of parameter sensitivity study. Summarizing the result ; ( 1 ) When the crack opening ratio U' is high, the effect of U' gets larger than any other except for the material factor m. But when U' is low, the effect is also diminished. Therefore, the selection of the lowest value possible is desirable in the evaluation of life. (2) When the value of the material factor m is high, the effect of crack opening ratio U' is increased, at the same time the effect of the other parameters also increased wholly. The effect of material factor m itself on life is high, but in case the material factor m is high, that the effect of each parameter on life get higher is unique. In designing, better attention to the material selection should be drawn. (3) In case the stress ratio R gets smaller, the effect of crack opening ratio U' is unchangeable. But the effect of R itself remarkably decreases, and the effect of material factor m somewhat decreases.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.1
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• pp.62-70
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• 2007

The development of new materials that are light-weight, yet high in strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress. The fatigue crack growth rate of the Shot-peened material was lower than that of the Un-peened material. And in stage I, threshold stress intensity factor of the shot-peen processed material is high in critical parts unlike the Un-peened material. Also, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than that of the Un-peened material. That is concluded from effect of da/dN. And Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.19-25
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• 1999

The research has extracted two kinds of specimen, one is rolling direction material(R-material) and the other rectangular of rolling direction(V-material), from Al alloy 7075 rolled. We have come to a conclusion by measuring crack propagation behavior with movement type microscope and Replica. 1) R-material shows 130% higher, approx. 39.2MPa in fatigue strength than V-material, approx. 29.4MPa. 2) In crack proportion, contrary to V-material growing directly toward specimen axis, R-material grows neared to shear direction. 3) The life proves that R-material is approx. 122% higher than V-material at 43.1MPa and approx. 135% higher at 47MPa. 4) The correlation between fatigue crack length and fracture life ratio applied to 'log(2a)=A+B ($N/N_f$)'equation shows inappropriate, because property value of Al alloy is low and the difference of chemical composition is high comparing with steel material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1991.10a
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• pp.83-89
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• 1991

The partial discharge properties of interface layer in Mica-Epoxy composite, which has been mainly used for the coil insulating material of high voltage machinery, are different from those of resins due to the abnormal interface layer to be presented between inorganic material and resin. Accordingly, the study on discharge of interface in composite insulting system is strongly requsted for not only an increasing of insulating strength, but also the basical information of diagnosis system for high voltage equipment. As a result, it has been confirmed that the interface is an abnormal resin layer and the contact states at interface is depended upon the density of silane aqueous solution. Pulse frequency at abnormal interface shows a linear increasing with enlargement of discharge quantity. Whereas, in case of normal interface, pulse frequency property represents exponential increasing at the point of saturating. A life model can be diagramed from results of time dependance of skewness, and a survival life time can be quantified from the life model suggested.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.228-229
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• 2005

The compressive residual stress, which is induced by shot peening process, has the effect of increasing the intrinsic fatigue strength of surface and therefore would be beneficial in reducing the probability of fatigue damage. However, it was not known that the effect of shot peening in corrosion environment. In this study, the effect of shot peening on corrosion fatigue crack growth of sping steel immersed in 6% $FeCl_3$ solution and corrosion characteristics with considering fracture mechanics. The results of the experimental study corrosion fatigue characteristics of spring steel are as follows; the fatigue crack growth rate of the shot peening material was lower than of the un peening material. And fatigue life shows more improvement in the shot peening material than un peening material. This is because the compressive residual stress of surface operate resistance of corrosion fatigue crack propagation. It is assumed that the shot peening process improve corrosive resistance and mechanical property.

• Journal of Ginseng Research
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• v.40 no.4
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• pp.395-399
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• 2016

Background: Korean ginseng (Panax ginseng) is one of the most important medicinal plants in the Orient. Among nine cultivars of P. ginseng, Chunpoong commands a much greater market value and has been planted widely in Korea. Chunpoong has superior quality "Chunsam" ($1^{st}$ grade ginseng) when made into red ginseng. Methods: A rapid and reliable method for discriminating the Chunpoong cultivar was developed by exploiting a single nucleotide polymorphism (SNP) in the auxin repressed protein gene of nine Korean ginseng cultivars using specific primers. Results: An SNP was detected between Chunpoong and other cultivars, and modified allele-specific primers were designed from this SNP site to specifically identify the Chunpoong cultivar and P. quinquefolius via multiplex polymerase chain reaction (PCR). Conclusion: These results suggest that great impact to prevent authentication of precise Chunpoong and other cultivars using the auxin repressed protein gene. We therefore present an effective method for the authentication of the Chunpoong cultivar of P. ginseng and P. quinquefolius.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.116-124
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• 2002

The fatigue life is predicted on tensile-shear spot weldment made from Al-Mg alloy sheet with thickness of 0.8mm using Mitchell's method and uniform material law by $B{\ddot{a}}umel$ and Seeger based on local strain approach. The fatigue properties of critical HAZ region are estimated from the tensile property using simple hardness method. To predict the fatigue life of spot weldment, the local stresses and strains at the potential critical region are estimated by Neuber's rule. The predicted fatigue life based on uniform material law using HAZ's material properties provides good results within a factor of 3, conservatively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1465-1473
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• 1994

This paper describes the development strategy and contents of a fatigue life evaluation system, FLEVA. The system is composed of 4 parts; material properties, load histories, cycle counting and life prediction. The cycle counting is based on the rain-flow counting method and peak counting method, and the life prediction is performed based on the linear damage rule. Material properties(static, fatigue) are also provided as a database obtained by a computer aided test system. Case study is performed to verify the developed program.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.05a
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• pp.49-51
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• 2012

This study was conducted as a part of database construction for development of CO₂ assessment system for concrete to assess CO₂ emissions and analyze characteristics of blast furnace slag manufactured in Korea through life cycle assessment method. For this, life cycle CO₂ emissions assessment technique for construction materials was examined. The entire manufacturing process for blast furnace slag was analyzed on blast furnace slag manufacturer in Korea for application of assessment technique. Life cycle CO₂ assessment was performed on blast furnace slag after classifying assessment process into raw material production step, raw material transportation step and construction material manufacture step.