• 한국해양공학회지
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• 제5권2호
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• pp.67-75
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• 1991

The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at $500^{\circ}C, 600^{\circ}C 700^{\circ}C$, and an applicability of stress intensity factor($K_I$), net section stress($\sigma_{net}$), $C^*$-ingegral and $C_t$ parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows: 1) Crack measurement by EP method was available and coincided with the Johnson, s analytical equation. 2) da/dt by $K_I$ and $\sigma_{net}$ was not adequate because of the wide scatter band according to load and temperature, but $C^*$-integral, except for transition region, was adequate. 3) $C_t$ parameter showed the best fitted line through total creep region without relating with both temperature and load condition. 4) Under the cyclic loading condition, $C_t$ parameter was proper to extimate da/dt. And it was shown that da/dt for 1% Cr-Mo V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.

• The Korean Journal of Pain
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• 제24권3호
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• pp.146-153
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• 2011

Background: Morphine has been commonly used for postoperative pain control. We measured plasma concentrations of morphine and compared the efficacy and safety of continuous epidural analgesia (CEA) using morphinebupivacaine with intravenous patient controlled analgesia (IV-PCA) with morphine for 48 hrs after the end of the operation. Methods: Nineteen patients undergoing Mile's operation were assigned to receive a morphine loading dose of 5 mg followed by IV-PCA with 0.1% morphine (IV-PCA group, n = 9) or a morphine loading dose of 2 mg and 0.125% bupivacaine 10 ml, followed by CEA with 0.004% morphine and 0.075% bupivacaine at a rate of 5 ml/hr (CEA group, n = 10). The plasma concentrations of morphine were measured and visual analog scales (VAS) for pain were recorded at 1, 6, 12, 24, and 48 hr postoperatively and the effects on respiration and any other side effects were noted. Results: The mean maximal and minimal levels of plasma morphine were $40.2{\pm}21.2\;ng/ml$ and $23.4{\pm}9.7\;ng/ml$ for the IV-PCA group and $11.8{\pm}3.5\;ng/ml$ and $8.2{\pm}1.9\;ng/ml$ for the CEA group, respectively. Resting and dynamic pain scores were significantly lower in the CEA group than in the IV-PCA group. There were no significant differences for the effects on respiration and for any side effects between the two groups. Conclusions: We evaluated plasma concentrations of morphine with CEA using morphine-bupivacaine and IV-PCA using morphine for the postoperative pain control. The CEA group had better postoperative analgesia than that of the IV-PCA group and the incidence of side effects were not significantly different between the two groups.

• 융합정보논문지
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• 제8권1호
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• pp.9-14
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• 2018

본 연구는 맨발 보행과 운동화 착용 보행에서 보행주기의 차이를 비교하여 보행역학에 따른 신발 개발에 기초자료를 제공하고자 한다. 발의 변형과 이상이 없는 정상 성인 여성 30명을 대상으로 보행 주기를 측정하였다. 먼저 운동화를 착용하고 보행하여 주기를 측정한 후, 맨발로 보행하여 주기를 측정하여 데이터를 얻었다. 이후 두 데이터를 대응표본 T-test를 이용하여 비교하였다. 실험 결과 맨발 보행에서 입각기 좌측(p<.001), 우측(p<.005), 체중부하기 좌측(p<.009), 우측(p<.002), 전유각기 좌측(p<.002), 우측(p<.011), 양하지 지지기(p<.004)가 증가하였고, 중간 입각기 좌측(p<.016), 우측(p<.001), 유각기 좌측(p<.001)이 감소하였다. 이는 맨발 보행이 다양한 발의 감각의 입력을 증가시켜 보행안정성이 높은 보행이 가능해 졌다고 보여 지며, 향후 보행 주기에 의거하여 맨발보행과 가까운 신발 개량이 필요하다고 사료된다. 향후 신발의 개량을 위해 신발 종류에 따른 보행주기 연구가 필요할 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제25권6호
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• pp.68-75
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• 2021

본 연구에서는 반복하중을 받는 외부 보-기둥 접합부에 정착된 57mm 확대머리철근의 정착성능을 평가하였다. 총 4개의 외부 보-기둥 접합부 실험체를 계획하였으며, 콘크리트 압축강도, 측면피복두께, 횡보강근비 및 파괴유형을 주요 실험 변수로 설정하여 정착성능평가를 수행하였다. 성능평가 결과, 접합부에 정착된 대구경 확대머리철근의 정착성능에 가장 큰 영향을 주는 요소는 측면피복두께 및 횡보강근으로 나타났으며, 외부 보-기둥 접합부에 정착된 57mm 대구경 확대머리철근은 반복하중하에서도 충분한 정착성능이 발현되는 것을 확인할 수 있었다.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.805-811
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• 2011

Aircraft MLG and wing structures have been recognized as fatigue critical structures and exposed to the risk of fatigue crack initiation and propagation. Furthermore, these structures are frequently subjected to serious dynamic loading condition during a Hard Landing which may lead to their failure. Especially, structural integrity of MLG and wing components is decreased as the flight time increased because of the fatigue damage accumulated on the aircraft. In this study, the effects of Hard Landing on the MLG and wing components of aging aircraft were evaluated by using numerical approach. To achieve the aim, a finite element model has been developed and simulations were conducted by varying the landing conditions. As a result, it was revealed that the high stress concentration phenomenon was occurred at the lower Side Brace of MLG. Thereby, the intensified inspection for the lower Side Brace should be considered to prevent unexpected aircraft mishap.

• 지질공학
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• 제8권3호
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• pp.215-224
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• 1998

LVDT에 의해 전체변형율이 측정되었고, 국부적 변형율은 변형율게이지에 의해 측정되었다. 또한 공시체에서의 응력 분포를 알기 위하여 유한요소법에 의한 축대칭 탄소성 해석을 하였다. 단면구속영향을 고려하면 H/D=1인 경우에 특히 구속영향을 크게 받는다. 또한 공시체 직경에 대한 공시체 길이가 길어질수록 영향을 적게 받는다는 것을 알 수 있다. 공시체와 재하판과의 접촉면에서 응력 및 변위 분포는 접촉하고 있는 두 재료의 탄성계수비와 접촉면의 마찰저항에 크게 좌우된다. 즉 암석공시체에 대한 재하판의 영향은 경암에서보다 연암에서 더 현저하다 또한 단면구속이 변형율 분포에 미치는 영향 및 치수효과는 강성이 큰 암석에서 현저하게 나타난다.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.141-155
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• 2014

The use of fiber reinforced polymer (FRP) composites in strengthening reinforced concrete beam-column subassemblies has been scrutinised both experimentally and numerically in recent years. While a multitude of numerical models are available, and many match the experimental results reasonably well, there are not many studies that have looked at the efficiency of different finite elements in a comparative way in order to clearly identify the best practice when it comes to modelling FRP for strengthening. The present study aims at investigating this within the context of FRP retrofitted reinforced concrete beam-column subassemblies. Two programs are used side by side; ANSYS and VecTor2. Results of the finite element modeling using these two programs are compared with a recent experimental study. Different failure and yield criteria along with different element types are implemented and a useful technique, which can reduce the number of elements considerably, is successfully employed for modeling planar structures subjected to in-plane loading in ANSYS. Comparison of the results shows that there is good agreement between ANSYS and VecTor2 results in monotonic loading. However, unlike VecTor2 program, implicit version of ANSYS program is not able to properly model the cyclic behavior of the modeled subassemblies. The paper will be useful to those who wish to study FRP strengthening applications numerically as it provides an insight into the choice of the elements and the methods of modeling to achieve desired accuracy and numerical stability, a matter not so clearly explored in the past in any of the published literature.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.221-229
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• 2004

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as $0^{circ},\;30^{circ},\;45^{circ},\;60^{circ}\;and\;90^{circ}$. The plastic zone expands more at the upper side of the composite beam than at the lower side for $30^{circ},\;45^{circ}\;and\;60^{circ}$ orientation angles. Residual stress components of ${\sigma}_{x}\;and \;{\tau}_{xy}$ are also found in the section of the composite beam.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.704-708
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• 1996

The elastic dynamic crack curving could be obtained by controlling the loading rate, the initial crack-tip blunting to store much energy before crack initiation and the magnitude of reflected wave from finite boundaries. However there is no theoretical and experimental elastic-plastic dynamic curving study. This paper proposes a specimen geometryfor a study of dynamic elastic-plastic crack curving and presents a preliminary result. The specimen has a blunt physical crack tip on a side, and a round notch tip on the other side. From the experiment using this specimen, it is found that the narrow plastic zone ahead of the round notch tip produces the change of load direction and anti-symmetricity of the dynamic isochromatics, and each result causes the crack curving phenomenon. After a certain time, as the elastic-plastic crack gets close to the round notch tip near, the degree of the crack curving get larger. The elastic reack curving propagates more sensitively to the surround of crack tip than the plastic crack curving does. The cynamic elastic-plastic crack curving is found to be proportional to the CTOA(the crack tip opening angle). The dynamic elastic-plastic crack may propagate in the direction perpendicular to the loading. An apparant strip yield zone which is similar to the Dugdale strip yield zone is noted ahead of the physical crack tip.

• Earthquakes and Structures
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• 제18권4호
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• pp.451-466
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• 2020

In this paper, the effect of Engineered Cementitious Composites (ECC) on the lateral strength of a bearing unreinforced Masonry (URM) wall, was experimentally and numerically investigated. Two half scale solid walls were constructed and were tested under quasi-static lateral loading. The first specimen was an un-retrofitted masonry wall (reference wall) while the second one was retrofitted by ECC mortar connected to the wall foundation via steel rebar dowels. The effect of pre-compression level, ECC layer thickness and one or double-side retrofitting on the URM wall lateral strength was numerically investigated. The validation of the numerical model was carried out from the experimental results. The results indicated that the application of ECC layer increases the wall lateral strength and the level of increment depends on the above mentioned parameters. Increasing pre-compression levels and the lack of connection between the ECC layer and the wall foundation reduces the influence of the ECC mortar on the wall lateral strength. In addition, the wall failure mode changes from flexure to the toe-crashing behavior. Furthermore, in the case of ECC layer connected to the wall foundation, the ECC layer thickness and double-side retrofitting showed a significant effect on the wall lateral strength. Finally, a simple method for estimating the lateral strength of retrofitted masonry walls is presented. The results of this method is in good agreement with the numerical results.