• Title/Summary/Keyword: tip radius

Search Result 155, Processing Time 0.027 seconds

A Numerical Approach to Young's Modulus Evaluation by Conical Indenter with Finite Tip-Radius (유한선단반경을 갖는 원뿔형 압입자에 의한 영률평가 수치접근법)

  • Lee, Jin-Haeng;Kim, Deok-Hoon;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.32 no.1
    • /
    • pp.35-42
    • /
    • 2008
  • Instrumented sharp indentation test is a well-directed method to measure hardness and elastic modulus. The sharp indenter such as Berkovich and conical indenters have a geometrical self-similarity in theory, but the self-similarity ceases to work in practice due to inevitable indenter tip-blunting. In this study we analyzed the load-depth curves of conical indenter with finite tip-radius via finite element method. Using the numerical regression data obtained from Kick's law, we first confirmed that loading curvature is significantly affected by tip radius as well as material properties. We then established a new method to evaluate Young's modulus, which successfully provides the value of elastic modulus with an average error of less than 2%, regardless of tip-radius and material properties of both indenter and specimen.

The Effects of Surface Energy and Roughness on Adhesion Force (표면에너지와 거칠기가 응착력에 미치는 영향)

  • Rha, Jong-Joo;Kwon, Sik-Cheol;Jeong, Yong-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.30 no.11 s.254
    • /
    • pp.1335-1347
    • /
    • 2006
  • Surface energies calculated from measured contact angles between several solutions and test samples, such as Si wafer, $Al_2O_3$, $SiO_2$, PTFE(Polytertrafluoroethylene), and DLC(Diamond Like Carbon) films, based on geometric mean method and Lewis acid base method. In order to relate roughness to adhesion force, surface roughness of test samples were scanned large area and small by AFM(Atomic Force Microscopy). Roughness was representative of test samples in large scan area and comparable with AFM tip radius in small scan area. Adhesion forces between AFM tip and test samples were matched well with order of roughness rather then surface energy. When AFM tips having different radius were used to measure adhesion force on DLCI film, sharper AFM tip was, smaller adhesion force was measured. Therefore contact area was more important factor to determine adhesion force.

Effect of Shockwave on Diesel Spray Characteristics in Ultra High Pressure Injection (극초고압 디젤분무의 충격파가 디젤분무특성에 미치는 영향)

  • Jeong, Dae-Yong;Lee, Jong-Tai
    • Journal of ILASS-Korea
    • /
    • v.10 no.1
    • /
    • pp.10-16
    • /
    • 2005
  • To investigate the effect of shockwave on diesel spray characteristics under ultra high pressure injection, the velocity of spray tip and shock wave were investigated using the visualization of spray by schlieren method. Spray characteristics such as the spray radius, height, and droplets size were analyzed. It is found in this study that shock wave, produced by ultra high injection pressure, propagates faster than spray tip. Spray radius of right side of nozzle tip was shorter than that of left side and spray height of right side of nozzle tip was thicker than that of left side. Droplets sue was increased at 414MPa in injection pressure because of pressure gradient between inner and outer of tile spray caused by shockwave.

  • PDF

Numerical Analysis of Tip Vortex Cavitation Behavior and Noise on Hydrofoil using Dissipation Vortex Model and Bubble Theory (소산이 고려된 보오텍스 모델과 버블 이론을 이용한 수중익 날개 끝 보오텍스 캐비테이션 거동 및 소음의 수치적 해석)

  • Park, Kwang-Kun;Seol, Han-Shin;Lee, Soo-Gab
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.43 no.2 s.146
    • /
    • pp.177-185
    • /
    • 2006
  • Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.

Material Transfer of MoS2 Wear Debris to Diamond Probe Tip in Nanoscale Wear test using Friction Force Microscopy (마찰력현미경을 이용한 나노스케일 마멸시험 시 다이아몬드 탐침으로의 MoS2 마멸입자 전이현상)

  • Song, Hyunjun;Lim, Hyeongwoo;Seong, Kwon Il;Ahn, Hyo Sok
    • Tribology and Lubricants
    • /
    • v.35 no.5
    • /
    • pp.286-293
    • /
    • 2019
  • In friction and wear tests that use friction force microscopy (FFM), the wear debris transfer to the tip apex that changes tip radius is a crucial issue that influences the friction and wear performances of films and coatings with nanoscale thicknesses. In this study, FFM tests are performed for bilayer $MoS_2$ film to obtain a better understanding of how geometrical and chemical changes of tip apex influence the friction and wear properties of nanoscale molecular layers. The critical load can be estimated from the test results based on the clear distinction of the failure area. Scanning electron microscopy and energy-dispersive spectroscopy are employed to measure and observe the geometrical and chemical changes of the tip apex. Under normal loads lower than 1000 nN, the reuse of tips enhances the friction and wear performance at the tip-sample interface as the contact pair changes with the increase of tip radius. Therefore, the reduction of contact pressure due to the increase of tip radius by the transfer of $MoS_2$ or Mo-dominant wear debris and the change of contact pairs from diamond/$MoS_2$ to partial $MoS_2$ or Mo/$MoS_2$ can explain the critical load increase that results from tip reuse. We suggest that the wear debris transfer to the tip apex should be considered when used tips are repeatedly employed to identify the tribological properties of ultra-thin films using FFM.

Microscopic fracture criterion of crack growth initiation (연성 균열성장 개시의 미시적 파괴조건)

  • 구인회
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.11 no.5
    • /
    • pp.740-745
    • /
    • 1987
  • For the prediction of the crack growth initiation from a blunt notch or a precrack in a prestrained material under plane strain tension and small-scale yielding conditions, a microscopic fracture criterion is proposed in terms of the crack tip opening displacement(COD) needed for the attainment of fracture strain at a microstructural distance. Smooth blunting of a crack tip with an initial root radius is assumed, and strain distributions on the crack-line axis are calculated at each deformation stage until the distributions against an original distance normalized to the COD are insensitive to an initial root radius. This case of no initial-root-radius effect is taken as for a sharp crack tip, on which the criterion is applied to determine the characteristic length of material from a critical COD for a fatigue-precracked specimen. The predicted COD at the fracture initiation from a crack with an initial root radius or a prestraining shows reasonable agreement with experimental values.

Nanoscale Processing on Silicon by Tribochemical Reaction

  • Kim, J.;Miyake, S.;Suzuki, K.
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
    • /
    • 2002.10b
    • /
    • pp.67-68
    • /
    • 2002
  • The properties and mechanism of silicon protuberance and groove processing by diamond tip sliding using atomic force microscope (AFM) in atmosphere were studied. To control the height of protuberance and the depth of groove, the processed height and depth depended on load and diamond tip radius were evaluated. Nanoprotuberances and grooves were fabricated on a silicon surface by approximately 100-nm-radius diamond tip sliding using an atomic force microscope in atmosphere. To clarify the mechanical and chemical properties of these parts processed, changes in the protuberance and groove profiles due to additional diamond tip sliding and potassium hydroxide (KOH) solution etching were evaluated. Processed protuberances were negligibly removed, and processed grooves were easily removed by additional diamond tip sliding. The KOH solution selectively etched the unprocessed silicon area. while the protuberances, grooves and flat surfaces processed by diamond tip sliding were negligibly etched. Three-dimensional nanofabrication is performed in this study by utilizing these mechanic-chemically processed parts as protective etching mask for KOH solution etching.

  • PDF

New Current-Voltage Model for Statistically Distributed Field Emitters

  • Lee, Myoung-Bok;Lee, Jae-Hoon;Kwon, Ki-Rock;Hahm, Sung-Ho;Lee, Jong-Hyun;Lee, Jung-Hee
    • 한국정보디스플레이학회:학술대회논문집
    • /
    • 2002.08a
    • /
    • pp.1039-1040
    • /
    • 2002
  • For the I-V modeling of sharp tip arrays and nanostructured planar emitters, we propose a new and much practical I-V relation including tip height and radius by considering a statistical distribution of tip radius. Frequently observed nonlinearity of Fowler-Nordheim plot for sharp tip and tip arrays was successfully simulated and then, an application example was provided to extract relevant emission-governing parameters of sharp tip.

  • PDF

A Study on the Wear of Diamond Stylus for Surface Roughness Measurement (표면거칠기 측정용 다이아몬드 촉침의 마모에 관한 연구)

  • Han, Eung-Kyo;Rho, Byung-Ok;Park, Du-Won;Kim, Jong-Ock
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.8 no.3
    • /
    • pp.105-113
    • /
    • 1991
  • The practicability of Ion-Sputter machining renders it possible to make diamond stylus for surface roughness measurement with micro stylus tip radius less than 2${\mu}mR$, and to measure surface roughness of fine-machined surface. In this study, we researched the wear or Ion-Sputtered stylus with 0.1${\mu}mR$ and 0.5${\mu}mR$ for micro-figure measurement and polished stylus with 0.5${\mu}mR$ according to measurement distance. As a result, we know that the case of Ion-Sputtered stylus is worn down easilier the case of polished stylus. And we know that in the evaluation of stylus wear, it is more useful method that examine the wear by measuring the variation of stylus tip radius than by evaluating the variation of Ra values.

  • PDF

Analysis of Measuring Error of Surface Roughness by Contact Stylus Profilometer (촉침에 의한 표면 거칠기 측정 오차 해석)

  • Cho, Nahm-Gyoo;Kwon, Ki-Hwan
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.16 no.12
    • /
    • pp.174-181
    • /
    • 1999
  • This paper describes the effect of the stylus tip size on the shape error in surface topography measurement. To analyze the distortional effect of an actual surface geometry origination from the finite stylus size, the surface is modeled as a sinusoid and the stylus tip as a circle. The magnitude of this distortion is defined as the ration of standard deviation, and this is expressed as an analytic function of the stylus tip radius and the geometrical parameter of a sinusoid. In this paper, the spectrum analysis of the profile is applied to investigate the distortional effect due to the mechanical filtering of the stylus in the frequency domain. and, the cumulative power spectrum is proposed to assess the shape error of measured data according to the various stylus tip sizes. From these results, a new method to select proper stylus tip radius is proposed.

  • PDF