• 한국압력기기공학회 논문집
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• 제13권2호
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• pp.75-83
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• 2017

In severe accident conditions of light water reactors, the loss of coolant may cause problems in integrity of zirconium fuel cladding. Under the condition of the loss of coolant, the zirconium fuel cladding can be exposed to high temperature steam and reacted with them by producing of hydrogen, which is caused by the failure in oxidation resistance of zirconium cladding materials during the loss of coolant accident scenarios. In order to avoid these problems, we develop a multi-metallic layered composite (MMLC) fuel cladding which compromises between the neutronic advantages of zirconium-based alloys and the accident-tolerance of non-zirconium-based metallic materials. Cold pilgering process is a common tube manufacturing process, which is complex material forming operation in highly non-steady state, where the materials undergo a long series of deformation resulting in both diameter and thickness reduction. During the cold pilgering process, MMLC claddings need to reduce the outside diameter and wall thickness. However, multi-layers of the tube are expected to occur different deformation processes because each layer has different mechanical properties. To improve the utilization of the pilgering process, 3-dimensional computational analyses have been made using a finite element modeling technique. We also analyze the dimensional change, strain and stress distribution at MMLC tube by considering the behavior of rolls such as stroke rate and feed rate.

• Journal of Biosystems Engineering
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• 제40권2호
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• pp.124-136
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• 2015

Purpose: Grain quality is a general concept that covers many characteristics, ranging from physical to biochemical and physiochemical properties. Rice aging during storage is currently a challenge in the rice industry, and is a complicated process involving changes in all of the above properties. Spectroscopic techniques can be used to obtain information on the quality of rice samples in a non-destructive manner. Methods: The objective of this review was to highlight the factors that contribute to rice quality and aging, and to describe various spectroscopic modalities, particularly vibrational and hyperspectral imaging, for the assessment of rice quality. Results: Starch and protein are the main components of the rice endosperm, and are therefore key factors contributing to eating and cooking quality. While the overall starch, protein, and lipid content in the rice grain remains essentially unchanged during storage, structural changes do occur. These changes affect pasting and gel properties, and ultimately the flavor of cooked rice. In addition, grain quality is significantly affected by growing and environmental conditions, such as water availability, temperature, fertilizer application, and salinity stress. These properties can be evaluated using spectroscopic techniques, and rice samples can be discriminated by using multivariate statistical analysis methods. Conclusion: Hyperspectral imaging and vibrational spectroscopy techniques have good potential for determining rice quality properties in a non-invasive manner, i.e., not requiring the introduction of instruments into the rice grain.

• 대한조선학회논문집
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• 제53권2호
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• 터널과지하공간
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• 제32권6호
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• pp.411-434
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• 2022

사용후핵연료의 심층처분 개념에서 근계영역 암반은 열-수리-역학적 복합거동을 하게 되는 것으로 잘 알려져있다. 이러한 복합거동 과정에서 암석의 여러 물성들은 변화하는데, 이러한 물성변화를 합리적으로 반영하는 경우 고준위방사성폐기물 처분장의 장기안정성의 평가를 위해 활용되는 해석 및 현장시험의 신뢰도를 향상시킬 수 있다. 이를 위해 본 기술보고에서는 암석의 열-수리-역학적 간접복합거동에 관한 국내외 연구사례를 조사하고 분석하였다. 특히, 간접복합거동의 대표적인 사례 중 지하수에 의한 포화 및 온도 증가에 따른 암석의 여러 물성 변화, 응력 변화에 의한 투수계수 변화를 중점적으로 조사·요약하였다.

• 한국지반공학회논문집
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• 제38권9호
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• pp.45-52
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• 2022

암반내 불연속면이나 지반-구조물의 접촉면은 열-수리-역학적으로 연계된 거동 특성을 보이므로, 온전한 지배방정식에 근거한 경계면 요소의 개발이 필요하다. 본 논문은 경계면 요소에 대한 힘평형 방정식, 유체의 연속방정식 그리고 에너지 평형 방정식을 유도하였다. 그리고 경계면 요소에 대한 탄소성 역학 모델의 강성행렬을 제시하였다. 개발된 유한요소는 2차원 조건에서 변위는 6절점, 수압과 온도는 4절점을 사용한다. 단층내 유체 주입에 대한 완전연계된 THM 해석은 단층내의 유효응력 감소와 주위 암반의 온도 수축에 의한 주입압의 복합적인 변화을 모델링 할수 있었다. 하지만, 열적 현상을 무시한 HM해석은 수리-역학적 변수를 과다하게 산정하였다.

• Journal of Korean Dental Science
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• 제16권1호
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• pp.23-34
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• 2023

Purpose: This study aims to investigate the force delivery profile of thermoformed aligners (TFA) compared with direct-printed aligners (DPA) and to explore the effect of different activation amounts on forces and moments of respective groups. A secondary objective is to observe the amount of stress relaxation that occurs over the 7~14 days when aligners are maintained in a simulated intraoral environment. Materials and Methods: An in vitro setup was created to quantify forces and moments. It consisted of a three dimensional-printed base plate and segmented maxillary teeth, placed in a semi-enclosed chamber to maintain a temperature of 37℃. Ninety clear aligners were divided into nine groups of ten aligners each based on material types (Zendura, ATMOS, TC-85) and activation amounts. Aligners were created with 0.00, 0.25- and 0.50-mm activations for lingual bodily movement of the upper left central incisor and kept on models in the "stressed" position in a 37℃ water bath. Three force components acting on the upper left lateral incisor, upper left central incisor, and upper right central incisor were measured for each time point, beginning from the initial baseline measurement, 8 hours, 16 hours, 24 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, and lastly, 14 days. Result: TC-85 aligners in every activation group showed less force on teeth than Zendura and ATMOS. Significant force levels from 0.0 mm activation were present and stayed consistent over the course of 14 days. Comparisons made for baseline measurements to 7-days and 14-days showed statistically significant change from the baseline force level. Conclusion: TC-85 aligners demonstrated lower, more consistent forces with fewer side effects. Aligners can generate forces even when no activation is programmed. No major decreases in force levels over time were observed; the intra-oral clinical simulated environment and length of observation time could contribute to this.

• Design & Manufacturing
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• 제17권3호
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• pp.8-14
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• 2023

In this study, basic research was conducted on manufacturing technology of thick-walled light guide a component that controls the light source of automobile lamps. As a preliminary study for manufacturing the final injection molded parts, a model for analyzing the influence of micro patterns on light guides is presented. The optical characteristics of the light guide were analyzed according to the change of the curvature radius of the micro-optical pattern, and the injection molding characteristics of the light guide according to the change of injection molding conditions were analytically evaluated. It was confirmed that the luminance uniformity improves as the R value decreases for changes in the micro-pattern R value, but it was confirmed that there are technical limitations in actual injection mold core processing and high-replication injection molding. Injection molding analysis showed that cooling channel design is very important compared to general injection molding due to thick-wall characteristics and thickness variation. It was also confirmed that the cooling channel has a great influence on the cycle time and birefringence result due to residual stress. As a result of analyzing the influence of filling time, holding condition, and cooling on shrinkage, it was found that the cooling water temperature has a significant effect on the shrinkage of ultra-fine light guide parts, and the holding condition also has a significant effect.

• 지질공학
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• 제25권1호
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• pp.93-102
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• 2015

지반은 동결이 발생함에 따라 물리적 특성이 변화하며, 동결현상에 따른 기초구조물의 안정성 평가는 설계시 중요한 고려사항 중 하나이다. 본 연구에서는 동결 및 전단과정 중 연직응력 변화에 따른 동결토의 전단강도 및 강성을 평가하고자 하였다. 동결토의 강도평가를 위하여 직접전단실험을 수행하였으며, 직접전단실험 중 강성평가를 위한 전단파 측정을 동시에 수행하였다. 실험수행을 위하여, 동결용 직접전단상자를 제작하였으며, 상·하부 전단상자의 벽면에는 전단파 트랜스듀서인 벤더 엘리먼트를 각각 설치하였다. 시료는 주문진사 및 실트, 그리고 증류수를 이용하여 포화도 10%로 혼합하였으며, 상대밀도가 모든 조건에서 동일하게 유지되도록 조성하였다. 조성된 시료는 -5℃까지 동결을 진행시킨 후, 온도를 유지한 상태로 직접전단실험을 수행하였다. 동결 및 전단과정 중 시료에는 다양한 크기의 연직응력이 가해졌으며, 전단과정 중 수평변위에 따른 전단응력 및 수직변위, 그리고 전단파를 측정하였다. 실험결과, 모든 구속조건의 경우에서 동결 혹은 전단과정의 연직응력이 증가함에 따라 전단강도는 증가하였으며, 전단과정의 연직응력만 증가한 경우보다 동결과정의 연직응력도 함께 증가한 경우 전단강도가 더 크게 증가하는 것으로 나타났다. 또한, 전단파 속도의 변화는 측정위치에 따라 다른 경향을 보였으며, 전단면을 통과하여 측정한 경우 전단파 속도는 전단변형이 진행됨에 따라 감소하는 것으로 나타났다. 본 연구는 동결 및 전단과정 시 구속조건의 효과를 평가한 연구로써, 포화도가 낮은 상태의 동결토의 강도 및 강성에 대한 기초자료로 활용될 수 있을 것으로 예상된다.

• 한국농공학회지
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• 제26권1호
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• pp.52-72
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• 1984

This study was performed to obtain the basic data which can be applied to the use of epoxy resin mortars. The data was based on the properties of epoxy resin mortars depending upon various mixing ratios to compare those of cement mortar. The resin which was used at this experiment was Epi-Bis type epoxy resin which is extensively being used as concrete structures. In the case of epoxy resin mortar, mixing ratios of resin to fine aggregate were 1: 2, 1: 4, 1: 6, 1: 8, 1:10, 1 :12 and 1:14, but the ratio of cement to fine aggregate in cement mortar was 1 : 2.5. The results obtained are summarized as follows; 1.When the mixing ratio was 1: 6, the highest density was 2.01 g/cm$^3$, being lower than 2.13 g/cm$^3$ of that of cement mortar. 2.According to the water absorption and water permeability test, the watertightness was shown very high at the mixing ratios of 1: 2, 1: 4 and 1: 6. But then the mixing ratio was less than 1 : 6, the watertightness considerably decreased. By this result, it was regarded that optimum mixing ratio of epoxy resin mortar for watertight structures should be richer mixing ratio than 1: 6. 3.The hardening shrinkage was large as the mixing ratio became leaner, but the values were remarkably small as compared with cement mortar. And the influence of dryness and moisture was exerted little at richer mixing ratio than 1: 6, but its effect was obvious at the lean mixing ratio, 1: 8, 1:10,1:12 and 1:14. It was confirmed that the optimum mixing ratio for concrete structures which would be influenced by the repeated dryness and moisture should be rich mixing ratio higher than 1: 6. 4.The compressive, bending and splitting tensile strenghs were observed very high, even the value at the mixing ratio of 1:14 was higher than that of cement mortar. It showed that epoxy resin mortar especially was to have high strength in bending and splitting tensile strength. Also, the initial strength within 24 hours gave rise to high value. Thus it was clear that epoxy resin was rapid hardening material. The multiple regression equations of strength were computed depending on a function of mixing ratios and curing times. 5.The elastic moduli derived from the compressive stress-strain curve were slightly smaller than the value of cement mortar, and the toughness of epoxy resin mortar was larger than that of cement mortar. 6.The impact resistance was strong compared with cement mortar at all mixing ratios. Especially, bending impact strength by the square pillar specimens was higher than the impact resistance of flat specimens or cylinderic specimens. 7.The Brinell hardness was relatively larger than that of cement mortar, but it gradually decreased with the decline of mixing ratio, and Brinell hardness at mixing ratio of 1 :14 was much the same as cement mortar. 8.The abrasion rate of epoxy resin mortar at all mixing ratio, when Losangeles abation testing machine revolved 500 times, was very low. Even mixing ratio of 1 :14 was no more than 31.41%, which was less than critical abrasion rate 40% of coarse aggregate for cement concrete. Consequently, the abrasion rate of epoxy resin mortar was superior to cement mortar, and the relation between abrasion rate and Brinell hardness was highly significant as exponential curve. 9.The highest bond strength of epoxy resin mortar was 12.9 kg/cm$^2$ at the mixing ratio of 1:2. The failure of bonded flat steel specimens occurred on the part of epoxy resin mortar at the mixing ratio of 1: 2 and 1: 4, and that of bonded cement concrete specimens was fond on the part of combained concrete at the mixing ratio of 1 : 2 ,1: 4 and 1: 6. It was confirmed that the optimum mixing ratio for bonding of steel plate, and of cement concrete should be rich mixing ratio above 1 : 4 and 1 : 6 respectively. 10.The variations of color tone by heating began to take place at about 60˚C, and the ultimate change occurred at 120˚C. The compressive, bending and splitting tensile strengths increased with rising temperature up to 80˚ C, but these rapidly decreased when temperature was above 800 C. Accordingly, it was evident that the resistance temperature of epoxy resin mortar was about 80˚C which was generally considered lower than that of the other concrete materials. But it is likely that there is no problem in epoxy resin mortar when used for unnecessary materials of high temperature resistance. The multiple regression equations of strength were computed depending on a function of mixing ratios and heating temperatures. 11.The susceptibility to chemical attack of cement mortar was easily affected by inorganic and organic acid. and that of epoxy resin mortar with mixing ratio of 1: 4 was of great resistance. On the other hand, when mixing ratio was lower than 1 : 8 epoxy resin mortar had very poor resistance, especially being poor resistant to organicacid. Therefore, for the structures requiring chemical resistance optimum mixing of epoxy resin mortar should be rich mixing ratio higher than 1: 4.

• 대한토목학회논문집
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• 제32권5A호
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• pp.307-315
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• 2012

최근 국내에서도 압축강도 180 MPa, 인장강도 10 MPa 이상의 초고성능 섬유보강 콘크리트(Ultra High Performance Fiber Reinforced Concrete, UHPFRC)가 개발되었다. 그러나 UHPFRC는 물-결합재비가 낮고 다량의 고분말 혼화재료를 혼입하며, 굵은 골재를 사용하지 않기 때문에 초기 재령에서의 자기수축이 크고, 표면이 급격히 건조하는 등 기존의 일반 콘크리트(Normal Concrete, NC) 및 고성능 콘크리트(High Performance Concrete, HPC)와는 다른 재료적 특성을 보인다. 그러므로 본 연구에서는 UHPFRC에 적합한 재료 실험 방법과 규정을 제안하고 극 초기 재령에서의 강도 특성을 평가하기 위하여 응결 및 수축, 인장 실험을 수행하였다. 응결 실험 결과 파라핀 오일을 UHPFRC의 모르타르 표면에 적용할 경우 표면에서의 급격한 건조현상을 효율적으로 억제할 수 있는 것으로 나타났으며, 시멘트와 배합수의 수화반응을 지연 또는 촉진 시키지 않는 것으로 나타나 응결 실험 시 표면건조 방지제로 적합한 것으로 판단되었다. 또한, 링-테스트를 수행하여 내부 강재 링의 온도와 변형률의 경향이 달라지는 시점을 수축 응력 발현 시점으로 정의하였으며, 이를 응결 실험과 비교하여 본 결과 응결침에 걸리는 관입 저항력이 약 1.5 MPa일 때 수축 응력이 발현되는 것으로 나타났다. 이는 초결 및 종결보다 약 0.6시간, 2.1시간 빠른 것이며, 상기 시점을 UHPFRC의 자기수축 측정 시점(time-zero)으로 규정하였다. 마지막으로, 본 연구에서는 극 초기 재령 인장강도 측정 장비를 제작하여 초결시점에서부터 UHPFRC의 인장강도와 탄성계수를 측정하였으며, 이를 고려한 UHPFRC의 인장강도 및 탄성계수 예측식을 제안하였다.