• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.281-287
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• 2011

We consider the uncertainty in the elastic buckling formula for a thin tube. We take into account the measurement uncertainty of Young's modulus and Poisson's ratio and the tolerance of the tube thickness and diameter. Elastic buckling must be prohibited for a thin tube such as a nuclear fuel rod that must satisfy a self-stand criterion. Since the predicted critical buckling pressure overestimated that found in the experiment, the determination of the minimum safety factor is crucial. The uncertainty in each parameter (i.e., Young's modulus, Poisson's ratio, thickness, and diameter) is mutually independent, so the safety factor is evaluated as the sum of the inverse of each uncertainty. We found that the thickness variation greatly affects the uncertainty. The minimum safety factor of a thin tube of Zirconium alloy is evaluated as 1.547 for a thickness of 0.87 mm and 3.487 for a thickness of 0.254 mm.

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.359-368
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• 2013

This paper presents a simplified analysis method using the elastic equivalent modelling not using the global finite element modelling of deck for the basic design GFRP composites deck with cellular tubes or sandwich structural type. In order to verify the validation of the simplified method ANSYS software package is used and compared the results analyzed on the global finite element modelling and the elastic equivalent modelling. And the laboratory testing by 4-point bending is conducted to compare the results based on the simplified analysis method proposed in this paper. The comparison of the results based on the analysis and the testing are discussed. It is found that the presented simplified analysis is applicable to the use in the basic design GFRP composite deck.

• Composites Research
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• v.37 no.2
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• pp.101-107
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• 2024

Demand for submarine cable is increasing due to advances in submarine power transmission technology and submarine cable manufacturing technology. Submarine cable use various types of protective equipment to prevent problems such as high maintenance costs in the event of cable damage and power outages during maintenance periods. Among them, flexible protection tube is a representative protective equipment to protect cables and respond to external forces such as waves and current. The flexible protection tube is made of polyurethane 85A hyperelastic material, so the calculation of mechanical behavior is carried out using mechanical properties based on experimental results. In this study, a study was conducted to determine the bending performance and tensile performance of flexible protection tube through analytical methods. The physical properties obtained through the multiaxial tensile test of polyurethane 85A were used for the analysis. Bending and tensile performance were determined for the maximum bending moment standard of 15 kN·m and the tensile load standard of 50 kN. As a result, it was confirmed that when the maximum bending moment of 15 kN·m of the flexible protection tube occurred, the bending performance of the MBR was secured at 13 m and when a tensile load of 50 kN, it was applied the maximum vertical displacement was 968 mm, confirming that the tensile performance was secured.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.315-318
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• 2003

Recently, condenser tube which is used for a cooling system of automobiles is mainly manufactured by the conform extrusion but this method is inferior as compared with direct extrusion in productivity per the unit time and in the equipment investment. Therefore, it is essential for the conversion of direct extrusion with porthole die. The direct extrusion with porthole die can produce condenser tube which has the competitive power in costs and qualities compared with the existing conform extrusion. This study is designed to evaluate metal flow, welding pressure, extrusion load tendency of mandrel deflection that is affected by variation of porthole shape in porthole die. Estimation is carried out using finite element method under the non-steady state. Also this study was examined into the cause of mandrel fracture through investigating elastic deformation of mandrel during the extrusion.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.66-72
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• 2003

In case of hollow cylinder extrusion using porthole die, the effects of extrusion parameters-temperature, the speed of extrusion, the shape of the die and mandrel-on metal flow in porthole die extrusion of aluminum have been investigated. However, there have been few studies about condenser tube extruded by porthole die. Original metal flow of condenser tube by porthole die extrusion is similar to hollow cylinder extrusion but the estimation of metal flow for extrusion parameters is different. For example, variation of chamber length in hollow extrusion only affects the welding pressure, however, the welding chamber length in condenser tube extrusion influences to the welding pressure as well as the deflection of mandrel. This study was designed to evaluate metal flow, welding pressure, extrusion load, tendency of mandrel deflection according to angular variation in the bottom of chamber in porthole die. Estimation was carried out using finite element method in as non-steady state. Analytical results can provide useful information the optimal design of porthole die.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.55.1-55.1
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• 2010

차세대 디스플레이용 전극 재료는 투명하면서도 낮은 저항값을 가져야 하는 투명 전극 재료로 금속, 금속산화물, 전도성 고분자, 탄소재료 등을 들 수 있다. 금속재료는 전도도는 우수하지만, 낮은 투과도로 투명전극 재료로 적절하지 않고, 대표적인 금속산화물 재료인 indium tin oxide (ITO)의 경우, 우수한 투과성과 낮은 면저항을 기반으로 차세대 디스플레이용 전극으로 현재 사용되고 있다. 하지만 ITO 박막은 휘거나 접을 때 기계적 안정성이 취약한 문제점을 나타내고 있다. 이러한 문제점을 극복하기 위해 전도성과 탄성계수가 높고, 저온에서 대면적 공정이 가능한 CNT을 투명 박막 전극 연구가 활발히 진행되고 있다. 하지만 투명전극 제조시, 탄소 나노튜브 간의 van der waals 인력에 의한 응집 현상으로 인한 분산의 불안정성과 분산제 사용으로 인하여 탄소 나노튜브 박막전극의 전기적, 광학적 특성이 저하를 야기한다. 이에 본 실험에서는 아크 방전 공정으로 합성한 SWCNT 분산액을 사용하여 spray coating 방법으로 glass 위에 박막을 형성하였다. SWCNT 투명 박막 전극 위에 DC sputtering을 이용하여 얇은Ni를 도포한 후, $450{\sim}500^{\circ}C$, ethylene gas 분위기의 thermal CVD방법으로 Carbon NanoFibers (CNFs)를 생성시킴과 동시에 분산제를 burning out하였다. CNF 성장 전후의 투명 박막의 전기적 특성은 four point probe를 이용하여 면저항과 UV-vis 장비를 이용하여 가시광선 영역에서의 광학적 투과도를 측정 비교하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.999-1005
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• 2011

The effects of strain-induced crystallization (SIC) on the mechanical properties of elastomeric composites as functions of extension ratio (${\lambda}$), multiwalled carbon nanotube (CNT) content, and carbon black (CB) content are investigated. The differential scanning calorimetry (DSC) analysis shows that the degree of crystallinity increases with the increase in the CB and CNT content. As ${\lambda}$ increases, the glass transition temperature (Tg) of the composites increases, and the latent heat of crystallization (LHc) of the composites is maximum at ${\lambda}$=1.5. It is found that the mechanical properties have a linear relation with LHc, depending on the CNT content. According to the TGA (thermogravimetric analysis), the weight loss of the composite matrix is 94.3% and the weight of the composites decreases with the filler content. The ratio of tensile modulus ($E_{comp}/E_{matrix}$) is higher than that of tensile strength (${\sigma}_{comp}/{\sigma}_{matrix}$) because of the CNT orientation inside the elastomeric composites.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.439-447
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• 2010

In this paper, the resonant characteristic of a Tonpilz transducer with a fixed tail mass has been researched and the feasibility to utilize the transducer in that resonant frequency has been analyzed. The additional resonance is occurred by adhering an elastic tube to the tail mass of a conventional Tonpilz transducer and fixing the other end of the tube. The characteristic of this low resonant mode is analyzed by means of the finite element method, then it is shown that this mode is affected by the variation of the stiffness of the tube as well as the mass of the head mass and tail mass. Based on the analysis results, the Tonpilz transducer is designed to meet specific performance conditions.

• Transactions of Materials Processing
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• v.15 no.5 s.86
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• pp.354-359
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• 2006

The elastomer forming process was employed for many operations which included piercing, sheet metal forming and tube metal forming process. This paper presents cylindrical tube forming process using rubber material such as polyurethane. For elastomer forming process, tensile tests at room temperature were performed to obtain the material properties of polyurethane and tube. In particular, biaxial tensile test were carried out to obtain the coefficient of strain energy function of the rubber material. Finite element analyses were also carried out to investigate the forming load and formability of tube. It was compared with the experimental results about the forming load and the formability of tube. From these results, it was investigated a forming process to decrease the forming load for elastomer forming process.