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우주 안테나용으로 연구 중인 열 자극 기반 형상기억폴리머로 된 축소 모형 안테나의 전개 실험을 수행하였다. 전개 실험을 위하여 양쪽 말단에 isocyanate기를 갖는 프리폴리머와 다관능기의 폴리올을 반응시켜 우레탄 형상기억폴리머를 합성하였으며, 2 mm의 두께를 갖는 원형 모양의 전개 시편을 제조하였다. 표면 부착형 가열 요소를 사용하여 형상기억폴리머 안테나 축소 모형을 전개한 결과, 가열요소의 크기와 방향 등에 따라 형상기억폴리머 시편의 온도 상승이 큰 차이를 나타내었다. 다양한 시도를 통하여 형상기억폴리머 시편을 전개시킬 수 있는 최적의 조건을 제시하였다. A deploying test of small-scale antenna models made of thermal stimulus-based shape memory polymer (SMP) was conducted; this material has been researched as a candidate for aerospace antenna applications. For the test, urethane SMP was synthesized from the prepolymer with diisocyanate and multi-functional polyol, and the circle-shaped specimens with a thickness of 2 mm were fabricated. The results of the deploying test of the SMP small-scale antenna model attached with heating element showed that the size and orientation of heating elements affect the temperature increase of the SMP specimens. The optimal attachment condition is suggested to deploy SMP effectively.
Energy can be reclaimed and stored for later use to recharge a battery or power a device through a process called energy harvesting. Piezoelectric is being widely investigated for use in harvesting energy from motion such as body movement and machine vibration. This paper presents a simple analytical model to describe output voltage effectiveness of a Piezo-Composite Generating Element (PCGE) from vibration and its experimental verification. PCGE is composed of layers of carbon/epoxy, PZT ceramic and glass/epoxy. During the manufacturing process, the stacked layers were cured at an elevated temperature of 177℃ in an autoclave, which made the PCGE pre-stressed due to a mismatch in the coefficients of thermal expansion between the constituent layers. For the experiments, three kinds of lay-up configurations of PCGE were utilized to verify the model and to approve its ability to convert oscillatory mechanical energy into electrical energy. The predicted performances are much in agreement with experimental ones.
In this study, the dynamic characteristic of an artificial wing mimicking an Allomyrina Dichotoma beetle's hind wing was investigated using a non-contact measurement method. The natural frequency, mode shape, and damping ratio of first two basic vibration modes in the operating frequency range were determined using a Bruel & Kjaer (B&K) fast Fourier transform analyzer along with a laser sensor. To confirm the results, a three-dimensional digital image correlation (3D-DIC) method along with high speed digital cameras was employed to construct the mode shapes of the wing when it was vibrated at pre-determined natural frequency. The mode shapes by DIC method showed a good agreement with those by laser displacement sensor. These results provide a method to investigate the modal analysis of a light weight structure like insect wing as well as construct the mode shape using DIC.
테이프래핑 구조물은 유도무기의 노즐 구조에 많이 사용되고 있는데 주로 주자직 복합재료를 띠모양으로 이은 다음 이를 맨드럴에 경사각을 가지게 감는 방법으로 제작된다. 적층된 구조물은 고압의 오토클레이브나 하이드로 클레이브에서 성형된다. 테이프래핑 구조물은 적층 형태가 일방향 복합재료의 경우와는 다르며, 제작 시 주어진 경사각을 고려한 해석이 필요하다. 본 연구에서는 테이프래핑 구조물에 대한 해석 기법을 고찰하였다. 먼저 4점 굽힘 실험에 대한 유한요소 해석 결과와 실험 결과를 비교함으로써 테이프래핑 구조물의 모델링 기법의 타당성을 검증하였다. 4점 굽힘 실험의 파단 하중과 이방성 파단 판정식의 결과를 비교함으로써 최적의 이방성 파단 판정식을 확인하였다. Tape-wrapped structures have been generally used in nozzle parts of guided missiles. A continuous band of woven composite material is wrapped around a mandrel that is designed to produce real products. After going through a vacuum bagging process, this woven composite material is cured in a high-pressure autoclave or hydroclave. However, tape-wrapped structures are difficult to analyze because of its large thickness and inclined lay-up. The present study investigates the method of analysis and failure prediction of tape-wrapped structures. The four-point bending test and its finite element analysis were performed to study how to model tape-wrapped structures and investigate their failure characteristics.
Thermal output is a big source of errors on measuring the thermal deformation of specimen when a strain gage is used. Although several methods have been developed and used to solve this problem, in the range of measuring temperature is limited. In this work, we introduce digital image correlation (DIC) technique to measure a full-field the thermal deformation of a aluminum plate. We compared the deformation results of DIC and strain gage to judge the capability of the DIC. Additionally, we measured the thermal deformation of a ring structure using DIC and the result was quite matched with theoretical solutions.
This presentation is focused on the introduction of a pre-stressed piezoelectric actuator, LIPCA (LIghtweight Piezo-Composite Actuator), which has been developed in 1999. The UPCA consists of a PZT ceramic wafer, carbon fiber composite layers with high modulus and near-zero CTE(coefficient of thermal expansion), and glass/epoxy layers with low modulus and high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by lightweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 ℃) after following an autoclave bagging process. The LIPCA has shown better actuation performance and the main 'reason for the good actuation displacement performance of the LIPCA is a compressive stress state occurs in the PZT layer due to a mismatch in the coefficient of thermal expansion during the curing process. In this presentation, the applications of the LIPCA to several engineering problems will be explained.
The nature can be the best source of learning tool for scientists to devise mechanical equivalents for the process of locomotion. Among various forms of forward swimming locomotion, the helical wave propulsion of flagella was successfully imitated from bacteria and proposed in this study. To evaluate the efficiency of this propulsion system, we designed and fabricated a biomimetic thruster and evaluated their thrust performance experimentally. Besides we considered the effect of “complex” filaments which comes from Rhizobium Meliloti bacteria to “plain” filaments on the thrust force produced by single flagellum at low Reynolds numbers. To compare the efficiency of propulsion together, an experimental setup was constructed to measure the thrust force produced by a single flagellum in silicone oil. The experimental results were in agreement with theoretical values predicted by the Resistance Force Theory (RFT) model and the maximum thrust force of complex flagellum were achieved at pitch angle of small helix q<SUB>s</SUB>=45°. In addition, we found that the thrust force generated by the complex flagellum has a value about 10 percent higher than that of plain flagellum with the same equivalent diameter.