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The objective of this study is to develop a unified, three-dimensional micromodel which can describe the nonlinear elastoplastic constitutive behavior of MMC's with continuous fibers, particles, or aligned short fibers as the reinforcement. In the micromodel, both the reinforcement and the matrix may has elastic and/or elastic deformation, respectively. However, as in most cases, the development is shown for elastic reinforcement in an elastoplastic matrix. The micromodel uses a repeating unit-cell model with eight subcells. For a particulate or an aligned short fiber composite, one center subcell represents the particle or the short fiber while the rest of the subcell represent the matrix. On the other hand, two aligned subcells indicate the fiber for a fibrous composite. The micromodel yields the overall effective constitutive equation for an MMC with elastoplastic deformation in the matrix material. The effective stress-strain plots of various MMC's are predicted using the micromodel for a wide variation of the reinforcement, volume fraction. These results are compared to those obtained from the finite element analysis, and the two results agree very well.
This study aims to find out cooling characteristics of TMA(Tri-Methyl-Amine, (CH₃)₃N) 25wt%-clathrate compound with ethanol(CH₃CH₂0H) such as supercooling, phase change temperature and specific heat. For this purpose, ethanol is added as per weight concentration and cooling experiment is performed at -6∼-8℃, cooling heat source temperature, and it leads the following result. (1) Phase change temperature is decreased due to freezing point depression phenomenon. Especially, it is minimized as 3.8 ℃ according to cooling source temperature in case that 0.5wt% of ethanol is added. (2) If 0.5wt% of ethanol is added, average supercooling degree is 0.9℃ and minimum supercooling is 0.8, 0.7℃ according to cooling heat source temperature. The restraint effect of supercooling is shown. (3) Specific heat shows tendency to decrease if ethanol is added. It is 3.013∼3.048 kJ/kgK according to cooling heat source temperature if 0.5wt% of ethanol is added. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound by adding additive, ethanol. This can lead to shorten refrigerator operation time of low temperature thermal storage system and improve COP of refrigerator and efficiency of overall system. Therefore energy can be saved and efficiency can be improved much more.
본 연구에서는 덤플형 내부 구조제를 가진 ISB 판넬의 굽힘 및 파손 특성을 분석/고찰하고자 한다. 딩플형 내부 구조체를 가진 ISB 판넬의 설계조건에 따른 변형 형상, 최대하중 및 최대하중에서의 변위와 같은 특성치 및 파손 형태를 분석하기 위하여 정적 3접 굽힘 시 험을 통한 하중-변위 곡선과 파손 형상을 얻었다. 또한, 본 실험 결과를 이용하여 ISB 판 넬 설계 변수의 굽힘 특성 및 파손 모드 영향성을 분석하였다. 본 연구 결과 딩플형 내부 구조체를 가진 ISB 판넬의 굽힘 및 파손 특성은 덤플형 내부구조체의 반경비와 ISB 판넬 의 재료 방향에 따라 제어 가능함을 알 수 있었다. The objective of this pater is to investigate into bending and failure characteristics of ISB panel with dimple shapes as inner structures. Through three-points bending test, the force-displacement curve and the failure shape are obtained to examine the deformation pattern, characteristic data including maximum load and displacement at the maximum load and failure pattern for the ISB panel. In addition, the influence of design parameters for ISB panel on the bending stiffness and failure mode has been found. From the results of the experiments, it has been shown that bending and failure characteristics of the ISB panel can be controlled by the ratio of radius and the direction of the material.
RT and UT are largely used as a non-destructive assessment of welding defects. RT shows difficulty in radioactive exposure and real-time detection. UT shows difficulty in quantitative detection of defects, and examination of a wide area in a short time. In order to settle the aforementioned disadvantages, many researchers try to find solution. In this paper, we apply a new examination method to verify the effectiveness in order to supplement the disadvantages of UT and RT, the existing non-destructive methods. The new method proposed in this paper is to use a difference in heat conductivity. If there is a discontinuous part, that is an internal defect. there is a difference in heat conductivity. Using this fact, it is possible to check the existence of an internal defect due to a temperature difference on the part with a defect and the part without a defect when the welded part is heated. The temperature difference on the surface indicated by the difference in heat conductivity can be checked for a wide area within a short time, by means of a thermal Image camera thereby to settle the disadvantage of the conventional non-destructive inspection methods. The thermal image method, however, has a disadvantage in that thermal load must be given to the tested sample and it is difficult to quantify measured data. In order to overcome this disadvantage, we will describe preliminary test and the like for applying thermal load on the tested sample including a welding defect, photographing images by means of a thermal image camera, analyzing thermal images, and analyzing welding defects.
Since a standard lens has small sight angle, a fish-eye lens can be used in order to obtain wide sight angle for the robot vision system. In spite of the advantage. the image through the lens has variable resolution; the central information of the lens is of high resolution, but the peripheral information is of low resolution. Owing to this difference of resolution, the variable resolution image should be transformed to a uniform resolution image in order to determine the positions of the objects in the image. In this work, the correction method using a neural network for the distorted image is presented and the performance is analyzed.
Existing test methods for thick-section specimens (4mm) have not provided precise compressive properties to date for the analysis and design of thick structure. A survey of the failure behavior of such thick specimens revealed that the failure initiated at the top corner of the specimen and propagated down and across the width of the specimen as premature failure, not typically reported for thin compression specimens. In the current study, the cause of the premature failure for thick specimens (T800/924C and IM7/8552) was identified experimentally and numerically. The premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Furthermore it was identified that the failure location within gauge section does not have an influence on the compressive strength from the experimental result performed with the unwaisted specimens (failure around junction of end tab and gauge section) and the waisted specimens (failure at the middle of gauge section). Finally, clear 1-D thickness and 3-D scaling effects on the compressive strength of unidirectional composite laminates existed. The main factors influencing the effects were due to manufacturing defects such as void content and fibre waviness.
Four solar stills that were fabricated each with cubes and glazing tilted angles of 15°, 30°, 45°, 60°, were compared with the quantities of condensed water. The quantities of condensed water were analysed with the weather conditions and temperatures for three months, On fine days, the quantity of average condensed water was more similar to those of 15° and 30°than to those of 45° and 60°, The quantity of condensed water produced by those of 45° and 60° were very irregular compared to those of 15° and 30", On rainy days, the quantity of condensed water was the most in that of 30° than those of the other angles and in cloudy, rainy and sunny conditions, the condensation quantity was the largest in that of 60°.
Conceptual structural design of the main wing for the 20 seats WIG(Wing in Ground Effect) flight vehicle, which will be a high speed maritime transportation system for the next generation, was performed. The high stiffness and strength Carbon-Epoxy material was used for the major structure and the skin-spar with a foam sandwich structural type was adopted for improvement of lightness and structural stability. As a design procedure for this study, firstly the design load was estimated with maximum flight load, and then flanges of the front and the rear spar from major bending load and the skin structure and the webs of the spars were preliminarily sized using the netting rules and the rule of mixture. In order to investigate the structural safety and stability, stress analysis was performed by Finite Element Codes such as NASTRAN/PATRAN and NISA II. From the stress analysis results, it was confirmed that the upper skin structure between the front spar and rear spar was very unstable for the buckling. Therefore in order to solve this problem, a middle spar and the foam sandwich structure at the upper skin and the web were added. After design modification. even thought the designed wing weight was a little bit heavier than the target wing weight, the structural safety and stability of the final design feature was confirmed. Moreover. in order to fix the wing structure at the fuselage, the insert bolt type structure with six high strength bolts was adopted for easy assembly and removal.
Door cursor is the important part which is located between the window and guide-rail and has a function which transfers the power of the window motor to window. The door cursor is made by the insert injection molding technology which can be used for the part which has insert core in the plastic molding. Because the heat from the injection mold can influence the size of the insert core, the insert injection molding is the difficult work and the need of computer simulation is increased to reduce the trial and error of mold. To investigate the various factor of the injection mold, three kinds of design of mold are proposed. The short-shot, temperature distribution, distortion, pressure distribution, weld line for each design are discussed. As a result, the Case 2 and Case 3 were proved as the better designs compared to the original one.
This study is performed to investigate the supercooling improvement and cooling characteristics change of TMA 25 wt% clathrate compound by additives as a low temperature storage material at -6℃ heat source. The used additives are acetone 0.3 wt%, ethylene glycol 0.2 wt% and ethanol 0.5 wt%. The experimental results showde that the phase change temperature is decreased by 0.1~1.6℃ in case of TMA 25 wt% clathrate compound with additives. Also the degree of supercooling is improved by 7. 2℃ in case of ethanol 0.5 wt%. Additionally the specific heat is decreased and the rate of volume change is increased when additives is added TMA 25 wt% clathrate compound.