• 한국해양공학회지
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• 제23권4호
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• pp.69-77
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• 2009

Structural analysis of a brake shoe for commercial vehicle was performed using finite element method. Since the strength of a brake shoe is affected by the magnitude and distribution shape of the contact pressure with the drum, the contact pressure between the shoe friction material and drum was calculated using a 2-Dimensional non-linear contact analysis in a state. And the brake was actuated by input air pressure and the drum of it was calculated both stationary and dynamic based on forced torque applied to the drum during the static state analysis. The results of the above analysis were then used as the load boundary conditions for a 3-Dimensional shoe model analysis to determine the maximum strain on the shoes. In the analysis model, the values of tensile test were used for the material properties of the brake shoes and drum, while the values of compression test were used for the friction material. We assumed it as linear variation, even though the properties of friction material were actually non-linear. The experiments were carried out under the same analysis conditions used for fatigue test and under the same brake system which equipped with a brake drum based on the actual axle state in a vehicle. The strains were measured at the same locations where the analysis was performed on the shoes. The obtained results of the experiment matched well with those from the analysis. Consequently, the model used in this study was able to determine the stress at the maximum air pressure at the braking system, thereby a modified shoe model in facilitating was satisfied with the required endurance strength in the vehicle.

• 대한기계학회논문집A
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• 제28권11호
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• pp.1711-1718
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• 2004

When the tracked vehicle is running on various types of terrain, the physical properties of the interacting ground can be different. In this paper, the interactions between track link and soft soil ground are investigated using static sinkage theory of soil ground. Grouser surfaces of a track link and triangular patches of ground are implemented for contact detection algorithm. Contact force at each segment area of a track link is computed respectively by using virtual work concept. Bekker's static soil sinkage model is applied for pressure-sinkage relationship and shear stress-shear displacement relationship proposed by Janosi and Hanamoto is used for tangential shear forces. The repetitive normal loads of a terrain are considered because a terrain element is subject to the repetitive loading of the roadwheels of a tracked vehicle. The methods how to apply Bekker's soil theory for multibody track system are proposed in this investigation and demonstrated numerically by high mobility tracked vehicle.

• Tribology and Lubricants
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• 제31권6호
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• pp.294-301
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• 2015

In this paper, we predict the rotordynamic force coefficients of tilting pad journal bearings (TPJBs) with rocker-back pivots, and we compare the predictions to recently published predictions and test data. The present TPJB model considers the rocker-back pivot stiffness calculated based on the Hertzian contact-stress theory, which is nonlinear with the application of a force . For the five-pad TPJB in load-between-pad and load-on-pad configurations, the predictions show the pressure- and film-thickness distributions, the deflection and stiffness of the individual pivots, and bearing stiffness and damping coefficients. The minimum film thickness and peak pressure occur at the bottom pad on which the applied load is directed. Because of the preload, the pres- sure is positive even at the upper pad in the opposite direction to the applied load. The pivot deflection and stiff- ness are maximum at the bottom pad that receives the heaviest pressure load. The predicted stiffness coefficients increase as the static load and rotor speed increase, while the damping coefficients decrease as the rotor speed increases, but increase as the static load increases. In general, the predicted stiffness coefficients agree well with the test data. The predicted damping coefficients overestimate the test data, particularly for large static loads. In general, the current predictive model considering the pivot stiffness improves the accuracy of the rotordynamic performance compared to previously reported models.

• Tribology and Lubricants
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• 제37권1호
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• pp.25-30
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• 2021

The surface texture produced via surface texturing is an important approach for controlling the tribological behavior of friction behavior of mechanical devices. The purpose of this study is to investigate the effect of grooves generated via ultrasonic nanocrystal surface modification (UNSM) technology on the tribological performance of AISI 4150 steel against stainless steel 316L. In the study, tribological tests are performed under two different regimes, namely mixed and hydrodynamic lubrication, by varying the applied normal load and reciprocating speed during the tests. According to the test results, the friction coefficient decreases as static load (10 N, 30 N, and 50 N) of UNSM technology increases in the mixed lubrication regime. Conversely, the friction coefficient increases as the static load (10 N, 30 N, and 50 N) of UNSM technology increases in the hydrodynamic lubrication regime. Hence, the results indicate that micro-grooves generate hydrodynamic pressure in the outlet, which increases the oil film thickness between the two mating surfaces. This potentially leads to a reduction in friction in the mixed lubrication regime due to the prevention of contact of asperities and debris. However, the results indicate an adverse effect in the hydrodynamic lubrication regime. In this regard, additional experiments should be performed to investigate the effect of grooves generated by UNSM technology at varying conditions on the friction behavior of AISI 4150 steel, which in turn can be controlled by the generated pressure and oil film thickness at the contact interface.

• Structural Engineering and Mechanics
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• 제30권3호
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• pp.263-278
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• 2008

Structural pipe-in-pipe cross-sections have significant potential for application in offshore oil and gas production systems because of their property that combines insulation performance with structural strength in an integrated way. Such cross-sections comprise inner and outer thin walled pipes with the annulus between them fully filled by a selectable thick filler material to impart an appropriate combination of properties. Structural pipe-in-pipe cross-sections can exhibit several different collapse mechanisms and the basis of the preferential occurrence of one over others is of interest. This paper presents an elastic analyses of a structural pipe-in-pipe cross-section when subjected to external hydrostatic pressure. It formulates and solves the static and elastic buckling problem using the variational principle of minimum potential energy. The paper also investigates a simplified formulation of the problem where the outer pipe and its contact with the filler material is considered as a 'pipe on an elastic foundation'. Results are presented to show the variation of elastic buckling pressure with the relative elastic modulus of the filler and pipe materials, the filler thickness and the thicknesses of the inner and outer pipes. The range of applicability of the simplified 'pipe on an elastic foundation' analysis is also presented. A brief review of the types of materials that could be used as the filler is combined with the results of the analysis to draw conclusions about elastic buckling behaviour of structural pipe-in-pipe cross-sections.

• 센서학회지
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• 제22권2호
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• pp.100-104
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• 2013

A superhydrophobic mesh is a unique structure that blocks water, while allowing gases, sound waves, and energy to pass through the holes in the mesh. This mesh is used in various devices, such as gas- and energy-permeable waterproof membranes for underwater sensors and electronic devices. However, it is difficult to fabricate micro- and nano-structures on three-dimensional surfaces, such as the cylindrical surface of a wire mesh. In this research, we successfully produced a superhydrophobic water-repellent mesh with a high contact angle (> $150^{\circ}$) for nanofibrous structures. Conducting polymer (CP) composite nanofibers were evenly coated on a stainless steel mesh surface, to create a superhydrophobic mesh with a pore size of $100{\mu}m$. The nanofiber structure could be controlled by the deposition time. As the deposition time increased, a high-density, hierarchical nanofiber structure was deposited on the mesh. The mesh surface was then coated with Teflon, to reduce the surface energy. The fabricated mesh had a static water contact angle of $163^{\circ}$, and a water-pressure resistance of 1.92 kPa.

• 한국항공우주학회지
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• 제39권8호
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• pp.719-724
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• 2011

비공기압 타이어(Non-Pneumatic tire)는 공기압 타이어와는 다르게 스포크(Spoke)로 공기압의 역할을 담당하는 새로운 타이어이다. 이 타이어는 공기압 타이어의 펑크에 대한 위험과 공기압 유지가 필요 없는 장접을 가졌으며, 공기가 존재하지 않는 우주에서도 사용이 가능하다. 본 연구에서는 음의 각으로 이뤄진 허니컴 구조의 비공기압 타이어를 수직 하중에 따른 접지압을 구하여, 이를 공기압 타이어와 비교하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.746-757
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• 2021

To investigate the mechanism of friction-induced vibration and noise of ship water lubricated stern bearings, a two-degree-of-freedom (2-DOF) nonlinear self-excited vibration model is established. The novelty of this work lies in the detailed analysis of influence of different parameters on the stability and nonlinear vibration characteristics of the system, which provides a theoretical basis for the various friction vibration and noise phenomenon and has a very important directive meaning for low noise design of water lubricated stern bearings. The results reveal that the change of any parameter, such as rotating speed of shaft, contact pressure, friction coefficient, system damping and stiffness, has an important influence on the stability and nonlinear response of the system. The vibration amplitudes of the system increase as (a) rotating speed of shaft, contact pressure, and the ratio of static friction coefficient to dynamic friction coefficient increase and (b) the transmission damping between motor and shaft decreases. The frequency spectrum of the system is modulated by the first mode natural frequency, which is continuous multi-harmonics of the first mode natural frequency. The response of the system presents a quasi-periodic motion.

• Composites Research
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• 제25권3호
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• pp.76-81
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• 2012

대기압 플라즈마 처리를 통해 탄소나노튜브(CNT) 표면은 개질 되며 개질된 입자의 표면과 탄소섬유 강화 CNT 페놀 복합재료간에 계면접착력에 변화를 확인하였다. CNT 표면에 플라즈마 처리에 따라 표면 변화가 발생되고 표면 개질의 결과를 확인하기 위해 FT-IR을 사용하였다. 또한, 정적 접촉각 실험법을 통해 플라즈마 처리에 따른 CNT의 젖음성을 비교 평가하였다. 순수 CNT 입자의 접촉각은 $118^{\circ}$ 였으나, 플라즈마 처리를 할 경우 $60^{\circ}$도로 표면 개질을 통해 젖음성이 향상됨을 확인하였다. 탄소섬유와 CNT-페놀복합재료 간 계면접착력은 플라즈마 처리에 따라 겉보기 강성도가 증가되는 결과를 확인하였으며, 음향방출 실험법과 전기저항 측정법을 병행한 이중기지평가법을 통해 계면전단강도 (IFSS)를 계산하여 계면접착력 향상을 확인하였다.

• 대한토목학회논문집
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• 제28권3A호
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• pp.357-366
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• 2008

본 연구는 교량 신축이음에 대해서 윤하중 재하실험을 통해 윤하중 재하 특성을 분석하고 이를 토대로 신축이음에서의 윤하중 재하기준을 마련하는 기초데이터를 확보하고자 실시하였다. 이를 위해 국내에서 많이 사용되고 있는 레일신축이음과 핑거신축이음에 대하여 시험체를 제작하고 실제 타이어 바퀴를 사용한 정적 윤하중 재하실험을 실시하였다. 윤하중에 접촉된 레일과 핑거에서 윤하중 분배율을 파악하였는데, 레일신축이음에서 중앙 레일이 지지하는 분담율은 윤하중 크기가 증가함에 따라 감소하는 것으로 나타났고 핑거신축이음에서는 접촉 면적 증가에 따라 거의 증가하지 않고 일정하게 됨을 알 수 있었다. 윤하중 재하 특성이 기존 설계기준과 많은 차이를 나타내고 있으므로 신축이음 설계를 위한 윤하중 접지압력 분포에 대한 합리적인 기준 마련이 필요하다고 판단되었다.