Beomkeun Kim

A flexible lead-free piezoelectric nanogenerator based on vertically aligned BaTiO3 nanotube arrays on a Ti-mesh substrate

A uniform piezoelectric film on a flexible substrate is highly desirable for the construction of mechanical energy harvesting devices and self-powered sensors. In this study, we synthesized piezoelectrically active tetragonal phase BaTiO3 (BTO) nanotube arrays uniformly coated on a flexible Ti-mesh substrate by in situ conversion of anodized TiO2 nanotubes using a low temperature hydrothermal process. The direct conversion of the TiO2 nanotube to tetragonal phase BTO provides an excellent way to make flexible composites with a uniform distribution and enhanced volume fraction of piezoelectrically active BTO film. Based on the merits of the tetragonal phase BTO film on a Ti-mesh substrate, a novel fully bendable and mechanically robust piezoelectric nanogenerator (PENG) was fabricated. The oriented tetragonal phase BTO nanotube film on the Ti-mesh substrate was encapsulated in a polydimethylsiloxane (PDMS) elastomeric layer and assembled between two indium tin oxide (ITO) coated polyethylene terephthalate (PET) electrodes to form a flexible PENG. The PENG device can harvest mechanical energy from repeated bending and releasing motions. The resulting output voltage and current reached up to 10.6 V and 1.1 μA, respectively. The output power generated was sufficient to instantaneously light a full screen liquid crystal display (LCD). The Ti-mesh/BTO-based PENG device is lead-free and does not have a toxic dispersion enhancer. It is a promising candidate for self-powered sensors and biomedical device applications.

Effect of a fastener hole design of inlet flanges on the durability of the exhaust manifold for a turbo-diesel engine

Abstract A clever design of fastener hole, which allows sliding behaviour, is investigated so as to understand the effect on the durability of the exhaust manifold for a turbo-diesel engine. Finite element analysis and experiments are performed to investigate the thermal deformation of the exhaust manifold with the fastener hole design. Temperature-dependent material properties of the exhaust manifold and sliding behaviour between the manifold and cylinder head are considered for the finite element model. A considerable amount of sliding between the manifold and cylinder head owing to the permanent deformation of the exhaust manifold are expected from the analysis. Experiments followed to verify results of the analysis. The plastic strain range, which is often used as the criterion for crack initiation, was estimated and compared with that of the exhaust manifold with a conventional fastener hole design, which does not allow sliding between the manifold and the cylinder head. Results revealed that a fastener hole design that allows sliding of the exhaust manifold, increases the durability of the exhaust manifold for the turbo-diesel engine.

Development of Mathematical Model to Predict Specific Wear Rates of Graphite Seal

ABSTRACT The dry sliding wear behavior of graphite that is used as the sealing material to cut off hot gas was evaluated as a function of applied load, sliding speed and temperature. The reciprocating wear tests were carried out at room temperature and elevated tempera tures. An attempt has been made to develop a mathematical model by response surface methodology and an analysis of variance technique was applied to confirm the validity of the developed model. Als o, the wear mechanism was compared through the observation of the worn surface by SEM analysis. 초 록 고온고압의 밸브에서 연소가스의 유입을 방지하는 흑연 씰은 밸브 축의 구동으로 인한 마찰 및 마모에 노출된다. 흑연 씰의 마모로 인해 고온 가스 제어가 불가능해지기 때문에 씰의 마모 특성을 예측하는 것은 매우 중요하다. 본 논문은 비마모율을 마모 특성에 대한 척도로 설정하고 접촉하중, 미끄럼 속도, 온도 등을 변수로 하여 흑연의 왕복동 마모 시험을 수행하였다. 반응표면분석법에 근거하여 실험계획을 정립하고 시험 결과에 대하여 분산분석법을 통하여 유효한 수학적 모델을 제시하였다. 또한, 마모 된 표면의 SEM 분석을 통해 특정 조건에서의 마모 메커니즘을 분석하고 비교하였다.Key Words: Graphite(흑연), Reciprocating Wear Test(왕복동 마모 시험), Specific Wear Rate(비마모율), Response Surface Methodology(반응표면분석법), Analysis of Variance(분산분석법)1. 서 론 내마모성이 뛰어난 흑연은 마찰 마모 기구에