• 지질공학
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• 제6권2호
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• pp.103-110
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• 1996

본 연구는 의성 소분지에 분포하는 백악기 사암과 셰일을 대상으로 압력에 따른 포아송비의 변화를 구명(究明)한 것이다. 역학적 시험을 실시하기 위하여, 직경 30.0Cm, 길이 6.2Cm인 시료를 사용하여 응력/변형률 시험을 하였다. 시험에 사용된 기기는 분해 능이 $10^{-7}$인 증폭기 및 16비트 A/D변환기,컴퓨터,하중 계측기,시험 운영 프로그램으로 구성되어 있으며, 유효자료 획득 속도는 매 초당 6~100개이다. 일반적으로 포아송비는 지금까지 하나의 물성으로 취급되어 왔으나, 본 시험 결과 금속류와는 달리 포아송비는 압력에 따라 변하는, 압력과 함수 관계에 있음이 확인되었다. 포아송비를 도출함에 있어서 4가지 방법을 사용한 결과, 계산에서는 포아송비가 급격하게 증가하여, 계산방법에 따라 파괴 영역이 확연히 구분되어 진다. 사암과 셰일은 낮은 하중과 높은 하중에서는 서로 다른 거동을 보였으나, 중간 하중 영역즉 탄성 한계 내에서는 ${\nu}_t={\nu}_0+P_{\sigma}$로(${\nu}_0$ : 탄성 영역 내에서의 초기 포아송비. ${\nu}_t$ : 탄성 영역 내에서의 포아송비, P : 포아송 계수, $\sigma$:응력)일차함수적으로 증가하였다. 2가지 암석 시료 모두 탄성 한계 내에서 포아송비는 0.1~0.21의 연속적인 변화 양상을 나타내며,파괴강도 65% 이사에서 급격히 증가하여 0.22~0.45로 나타나므로 이는 탄성 범위밖에 해당된다.

• Journal of Welding and Joining
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• 제15권4호
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• pp.187-193
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• 1997

In the weldmentsm the crack propagation rate is changed due to the residual stress. The crack propagation rate is high in the region with the residual stress. However it shows rhw same behavior with the base metal in the region that does not include the residual stress. The fatigue crack growth rate for the material with residual stresses can be predicted more precisely by using the effective stress ratio. The difference between experimental results and prediction results in the initial stage seems to be due to the redistribution of residual stresses and microstructural change.

• Geomechanics and Engineering
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• 제8권6호
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• pp.783-799
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• 2015

In this study, effect of horizontal in situ stress on failure mechanism around underground openings excavated in isotropic, elastic rock zones is investigated. For estimating the plastic zone occurrence, an induced stress influence area approach (Bray Equations) was modified to define critical stress ratio according to the Mohr-Coulomb failure criterion. Results obtained from modified calculations were compared with results of some other analytical solutions for plastic zone thickness estimation and the numerical modelling (finite difference method software, FLAC2D) study. Plastic zone and its geometry around tunnels were analyzed for different in situ stress conditions. The modified equations gave similar results with those obtained from the other approaches. However, safer results were calculated using the modified equations for high in situ stress conditions and excessive ratio of horizontal to vertical in situ stresses. As the outcome of this study, the modified equations are suggested to use for estimating the plastic zone occurrence and its thickness around the tunnels with circular cross-section.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1434-1437
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• 2003

Sometimes open holes are required for the function and the weight reduction of structure and machinery. However, the serious stress concentration occurs because of the geometric discontinuity caused by the holes and cutting section. In this study, it is attempted to obtain the stress concentration coefficients of the inner surface of the hole boundary by changing the position and the shape of holes on the homogeneous isotropic plate. And the effects on the plate are investigated. The results show that the stress level becomes low and the distribution area widens the position of stress concentration changes as the ratio a/b increases and change to a circle. And as the ratio a/l decreases, the stress concentration reduces. As the plate with three holes. the stress $\sigma$$\_$x/ and $\tau$$\_$xy/ of hole 1,3 becomes high, especially $\sigma$$\_$x/ dominant and high.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.833-836
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• 2002

Sometimes open holes are required for the function and the weight reduction of structure and machinery. However, the serious stress concentration occurs because of the geometric discontinuity caused by the holes and cutting section. In this study, it is attempted to obtain the stress concentration coefficients of the inner surface of the hole boundary by changing the position and the shape of holes on the homogeneous isotropic plate. And the effects on the plate are investigated. The results show that the stress level becomes low and the distribution area widens the position of stress concentration changes as the ratio ah increases and change to a circle. And as the ratio a/l decreases, the stress concentration reduces.

• 동의신경정신과학회지
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• 제20권1호
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• pp.165-176
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• 2009

Objectives : The purpose of this study was to assess the effects of mental stress stimulation and acupucnture applied at HT7 point on heart rate variability (HRV) in normal subjects. Methods : Thirty seven healthy volunteers participated in this study. The volunteers were randomly allocated into two groups. Both groups performed a mental arithmetic stress test and stroop color-word test for 10 minute. Then, acupuncture needles were inserted on HT7 for the study group and on non-acupucnture point for the control group. HRV was recorded three times at test time and before and after acupuncture stimulation. Results : After giving mental stress stimulation to both groups, LF and LF!HF ratio were increased and HF was decreased significantly. After giving acupuncture to study group, LF and LF/HF ratio were decreased and HF was increased, but it was not significant. After giving acupuncture to control group, LF and LF/HF ratio were increased and HF was decreased, but it was not significant. Conclusions : This results show that mental arithmetic stress test and stroop color-word test contribute to activation of the sympathetic nervous system Acupuncture at HT7 could be relatively useful to decrease sympathetic activity and balance autonomic nervous system for those who are under stress.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.385-393
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• 2007

The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.

• Journal of the Korean Wood Science and Technology
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• 제32권3호
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• pp.33-41
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• 2004

In ancient wooden structures, the mechanical properties of the structural members have been reduced by time-dependent degradations such as fatigue or creep. Also, the external and internal deterioration was caused by environmental condition, fungi, bacteria, or insect, and then reduced the quality of structural members. However, the previous methods for evaluating the deterioration have been mainly depended on the visual inspection. In this study, therefore, ultrasonic stress wave test, accelerometer stress wave test were used to evaluate the deterioration of structural wood members in ancient wooden structures. Based on the results, the quantitative criteria of stress wave transmitted velocity were proposed to evaluate the deterioration of structural member. The proposed criteria were related to the degree of deterioration. In accelerometer stress wave, the criteria of deterioration of wave reciprocal velocity was below 1800 ㎲/m at incipient deterioration (below 12% ratio of deterioration), between 1800 and 2200 ㎲/m at moderate deterioration (12~17%) and above 2200 ㎲/m at severe deterioration (above 17%). The ultrasonic stress wave, the criteria of deterioration were 800 and 950 ㎲/m at below 8% and above 15% of the degree of deterioration respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.560-565
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• 2001

The objective of the present study is to investigate the characteristics for flow and wall shear stress in the aneurysm which is a local dilatation of the blood vessel. The numerical simulation using the commercial software for the laminar and steady flow were carried out over the diameter ratios(ratio of maximum diameter of aneurysm to the diameter of blood vessel) ranging from 1.5 to 2.5 and Reynolds number ranging from 900 to 1800. It was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. Especially, for the Reynolds number of 1800 and diameter ratio of 2.5, the very weak secondary recirculating flow was produced at the left upper of the aneurysm. The position of a maximum wall shear stress was the distal end of the aneurysm(z=18mm) regardless of the Reynolds number and diameter ratios. But the maximum values of the wall shear stress increased in proportion to the increase of Reynolds number and diameter ratio.

• 동력기계공학회지
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• 제15권1호
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• pp.39-44
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• 2011

This study was to investigate the effects of stress ratio and anisotropy on Fatigue Crack Propagation(FCP) behavior of rolled magnesium alloy AZ31B. The experimental materials were a Mg-Al-Zn magnesium alloy. The FCP test was conducted on compact tension specimen by a servo-hydraulic fatigue testing machine in air at room temperature. Compact tension specimens were prepared from the extruded parallel and vertical rolling direction. The test condition was frequency of 10Hz and sinusoidal load stress ratios are 0.1 and 0.7. The FCP rates was automatically measured by a compliance method. In the case of the FCP of AZ31B, the FCP of both direction of LT and TL by anisotropy of specimens are almost same value. In lower stress ratio, the FCP of the LT, TL specimens are increased in lower ${\Delta}K$ region but higher ${\Delta}K$ regions are almost same value. Finally, the result of observed the surface crack, it expressed the quasi-cleavage fracture in lower ${\Delta}K$ region and straight mark on the aspect of the facet in high ${\Delta}K$ region.