• 대한기계학회논문집A
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• 제24권7호
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• pp.1863-1870
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• 2000

When an impact stress is applied on the external boundary of double cantilever beam of orthotropic material which crack length is greater than specimen hight and anistropic ratio is very high, dyna mic energy release rate is derived, and the relationship between dynamic energy release rate and crack propagating velocity is studied. Dynamic energy release rate to static energy release rate is decreased with increasment of crack propagating velocity. The relationships between dynamic energy release rate and vertical strain have a similar pattern with those between static energy release rate and vertical strain. When normalized time(Cstla) is greater than or equal to 2, dynamic energy release rate approaches to a constant value.

• 대한기계학회논문집
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• 제19권1호
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• pp.170-180
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• 1995

A parallel crack in bonded dissimilar orthotropic planes under out-of-plane loading is analyzed. The problem is formulated by Fourier integral transforms, and reduced to a pair of dual integral equations. By solving the integral equations, the asymptotic stress and displacement fields near the crack tip are determined in closed form, from which the stress intensity factor and energy release rate are obtained. Discontinuity in the stress intensity factor as the distance ratio h/a of the parallel crack approaches zero is found, while the energy releas rate is shown to be continuous at h/a = 0. This information can immediately be used to generate the stress intensity factor for the parallel crack near the interface. By employing "the maximum energy release rate criterion", it could be shown in the case of no existing crack initially that the parallel crack is formed far from the interface for the more compliant material, while it is formed close to the interface for the stiffer material. material.

• 대한본초학회지
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• 제28권4호
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• pp.57-62
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• 2013

Objectives : Lonicerae Japonicae Flos (LJF) has been shown anti-oxidant, anti-inflammatory, anti-viral, anti-rheumatoid properties. However, it is still largely unknown whether LJF inhibits skin injury against oxidative stress in human keratinocyte, HaCaT cells. The purpose of this study was to evaluate the protective effects of LJF against hydrogen peroxide($H_2O_2$)-induced oxidative stress in human keratinocytes, HaCaT cells. Methods : To evaluate out the protective effects of LJF on oxidative injury in HaCaT cells, an oxidative stress model of HaCaT cells was established under a suitable concentration (500 ${\mu}M$) hydrogen peroxide. HaCaT keratinocyte cells were pre-treated with LJF (0.1, 0.25 or 0.5 mg/ml), and then stimulated with $H_2O_2$. Then, the cells were harvested to measure the cell viability, DNA damage, and release of reactive oxygen species (ROS). Results : LJF (0.1, 0.25 or 0.5 mg/ml) itself did not show any significant toxicity in HaCaT cells. The treatment of $H_2O_2$ caused the oxidative stress, leading to the cell death, and DNA injury. However, pretreatment with LJF reduced cell death, and DNA injury. The stimulation of $H_2O_2$ on HaCaT cells resulted in excessive release of ROS, which is the main factor of oxidative stress. The excessive release of ROS was inhibited by LJF treatment significantly. Conclusions : These results could suggest that LJF exhibited the protective effects of HaCaT cells against $H_2O_2$-induced oxidative stress by inhibiting ROS release. It could be explained that LJF inhibit skin damages against oxidative stress. Thus, LJF would be useful for the development of drug or cosmetics treating skin troubles.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.721-725
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• 1996

The microfabricated test structures were used in order to evaluate the stress characteristics in films. The test structures were fabricated using surface micromachining technique, including HF vapor phase etching as an effective release method. The fabricated structures were micro strain gauge, cantilever-type vernier gauge and bridge for stress measurement, and cantilever for stress gradient measurement. The strain was measures by observing the deformation of the structures occurred after release etching and the amount of deformation can be detected by micro vernier gauge, which has gauge resolution of 0.2${\mu}{\textrm}{m}$. The detection principles and the degree of precision for the measured strain were also discussed. The characteristics of residual stress in LPCVD polysilicon films were studied using these test structures. The stress gradient due to the stress variation through the film thickness was calculated by measuring the deflection at the cantilever free end.

• 대한기계학회논문집
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• 제17권2호
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• pp.331-341
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• 1993

The propagating crack problems under dynamic antiplane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems by theoretical method or experimental method in orthotropic material, it is important to know the dynamic stress intensity factor in the vicinity of crack tip. Therefore the dynamic stress field and dynamic displacement field with dynamic stress intensity factor of orthotropic material in mode III were derived. When the crack propagation speed approachs to zero, the dynamic stress components and dynamic displacement components derived in this paper are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determined by using the concept of crack closure energy with the dynamic stresses and dynamic displacements derived in this paper. Finally, the characteristics of crack propagation are studied with the properties of orthotropic material and crack speed. The variation of angle .alpha. between fiber direction and crack propagating direction and crack propagation speed fairly effect on stress component and displacement component in crack tip. The influence of crack propagation speed on the speed on the stress and displacement is greater in the case of .alpha.=90.deg. than in the case of .alpha.=0.deg. and the faster the crack propagation speed, the greater the stress value and displacement value.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.378-383
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non-coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• Structural Engineering and Mechanics
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• 제25권6호
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• pp.733-751
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• 2007

The metis element method (Hung 1978) has been applied to analyse free edge interlaminar stresses and delamination in composite laminates, which are subjected to extension and bending. The paper recalls Lekhnitskii's solution for generalized plane strain state of composite laminate and Wang's singular solution for determination of stress singularity order and of eigen coefficients $C_m$ for delamination problem. Then the formulae of metis displacement finite element in two-dimensional problem are established. Computation of the stress intensity factors and the energy release rates are presented in details. The energy release rate, G, is computed by Irwin's virtual crack technique using metis elements. Finally, results of interlaminar stresses, the three stress intensity factors and the energy release rates for delamination crack in composite laminates under extension and bending are illustrated and compared with the literature to demonstrate the efficiency of the present method.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.29-32
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non- coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• 생약학회지
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• 제20권1호
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• pp.37-42
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• 1989

This study was carried out to investigate the effect of Glycyrrhizae Radix on serum corticosterone and blood histamine content by immobilization stress in mice. Corticosterone secretion and blood histamine level was significantly increased in mice by subjecting the animals to immobilization stress 1 hr. after intraperitoneal injection of Glycyrrhizae Radix extract (150 mg/kg) and glycyrrhizinic and (15 mg/kg). whereas, administration of cortisol $(7.5\;{\mu}g/kg)$ provoked a decrease in corticosterone secretion and histamine levels. These results suggested that glycyrrhizinic acid was effective on cortiosterone release provoked by immobilization stress and this release was mediated in part by histamine.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.752-754
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• 1997

The stress intensity factor for an interface crack in dissimilar materials has been obtained by many researchers. But research of the energy release rate for an interface crack in pseudo-isotropic dissimilar materials is insufficient yet. In this paper, the energy release rate for cracks in pseudo-isotropic dissimilar materials was obtained using eigenfunction expansion method and also analyzed numerically using the reciprocal work contour integral method. The results were verified by comparing with other worker's results.