• Title/Summary/Keyword: micro-stress

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A Study on the Plane Couette Flow Using Micropolar Fluid Theory

  • Kim, Youn-Jea;Kim, Tae-An
    • Journal of Mechanical Science and Technology
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    • v.18 no.3
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    • pp.491-498
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    • 2004
  • An analysis of the plane Couette flow between two parallel plates of a viscous, incompressible, micropolar fluid is presented. Especially, the effects of non-zero values of the micro-gyration boundary condition coefficient and pressure gradient on the flow fields are studied. Numerical results show that the micro polar parameter was found to have much more of an impact on the flow behaviors. It is also observed that the micro-gyration boundary condition coefficient influenced on the coefficients of skin friction and couple stress due to its different effect on the surface stress.

Finite Element Analysis for Shape Prediction on Micro Lens Forming (마이크로 렌즈 성형시 형상예측을 위한 유한요소해석)

  • 전병희;홍석관;표창률
    • Transactions of Materials Processing
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    • v.11 no.7
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    • pp.581-588
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    • 2002
  • Among the processes to produce micro lens, the process using press molding is a new technology to simplify the process, but it contains many unknown variables. The press-molding process proposed in this paper was simplified into two step process, the first step is the pressing to design the preform for glass element, the second step is the annealing to reduce the residual stress. It is important to estimate the amount of shrinkage of glass gob and the residual stress during process. It Is difficult to evaluate the process variables as mentioned above through the experiment. The influences due to process variables was evaluated by using FEM parametric analysis. The results in this paper can be applicable to produce micro lens.

Fabrication of a Micro Actuator with p$^+$ Si Cantilevers for Optical Devices (p$^+$ Si 외팔보 구조를 이용한 광학 소자용 마이크로 구동기의 제작)

  • Park, Tae-Gyu;Yang, Sang-Sik
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.50 no.5
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    • pp.249-252
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    • 2001
  • The paper represents the design and fabrication of an electrostatic micro actuator with $p^+$,/TEX> Si cantilevers. The micro actuator consists of a plate suspended by four $p^+$,/TEX> silicon cantilevers and an electrode on a glass substrate. The $p^+$,/TEX> Si structure is fabricated by the boron diffusion process and the anisotropic wet etch process. The cantilevers of the micro actuator curl down because of the residual stress gradient in $p^+$,/TEX> silicon. When the electrostatic forec is applied to the $p^+$,/TEX> cantilevers, the vertical displacement of the plate can be achieved. The deflection of the cantilever due to the residual stress gradient and the vertical displacement by electrostatic force were calculated. The displacement of the plate was measured with a laser displacement meter for various input voltages and frequencies. The feasibility of the proposed micro actuator for the applications to optical pickup devices or optical communication devices was confirmed by the experiments.

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A New Antistiction Method Using Polymer Suspension for Fabrication with Polysilicon Micromachining (다결정 실리콘 마이크로머시닝 제작 시 폴리머 지지를 이용한 옆 방향 정착방지 방법의 제안)

  • Lim, Hyung-Taek;Yoon, Choong-Hyun;Kim, Yong-Kweon
    • Proceedings of the KIEE Conference
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    • 1999.07g
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    • pp.3331-3333
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    • 1999
  • A novel antistiction method using photo resist is proposed and verified to improve the yield of polysilicon micromachining process. $7.5{\mu}m-thick$ polysilicon is used as a structural layer. Residual stress and stress gradient originated from polysilicon deposition with LPCVD process is relaxed by doping and thermal treatment. The stress gradient of stress-free polysilicon layer is $-0.755MPa/{\mu}m$.

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Fatigue crack behavior under constant stress and periodic overstressing (일정응력 및 과대과소응력하에서의 피로크랙 발생전파거동)

  • 송삼홍;이경노
    • Journal of the korean Society of Automotive Engineers
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    • v.13 no.1
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    • pp.57-65
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    • 1991
  • It is experimented under rotary bending stress that the spacing of two micro hole flaws is adjacent and that it is distant. In order to observe the behavior of fatigue crack propagation, two kinds of specimens are tested under constant stress and periodic overstressing. Although the crack occurs faster when two micro-hole flaws are adjacent than when they are distant, but there is no difference of the number of fracture cycles between two. The crack propagates slower under low-high block stress than under high-constant stress, and it propagates faster under high-low block stress than under low-constant stress. The influence of two-step block stress is serious right after the stress varies.

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Buckling and vibration of porous sandwich microactuator-microsensor with three-phase carbon nanotubes/fiber/polymer piezoelectric polymeric nanocomposite face sheets

  • Arani, Ali Ghorbanpour;Navi, Borhan Rousta;Mohammadimehr, Mehdi
    • Steel and Composite Structures
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    • v.41 no.6
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    • pp.805-820
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    • 2021
  • In this research, the buckling and free vibration of three-phase carbon nanotubes/ fiber/ polymer piezoelectric nanocomposite face sheet sandwich microbeam with microsensor and micro-actuator surrounded in elastic foundation based on modified couple stress theory (MCST) is investigated. Three types of porous materials are considered for sandwich core. Higher order (Reddy) and sinusoidal shear deformation beam theories are employed for the displacement fields. Sinusoidal surface stress effects are extracted for sinusoidal shear deformation beam theory. The equations of motion are derived by Hamilton's principle and then the natural frequency and critical buckling load are obtained by Navier's type solution. The determined results are in good agreement with other literatures. The detailed numerical investigation for various parameters is performed for this microsensor-microactuator. The results reveal that the microsensor-microactuator enhanced by increasing of Skempton coefficient, carbon nanotubes diameter length to thickness ratio, small scale factor, elastic foundation, surface stress constants and reduction in porous coefficient, micro-actuator voltage and CNT weight fraction. The valuable results can be expedient for micro-electro-mechanical (MEMS) and nano-electro-mechanical (NEMS) systems.

Stress Measurement of films using surface micromachined test structures (표면 미세 가공된 구조체를 이용한 박막의 응력 측정)

  • 이창승;정회환;노광수;이종현;유형준
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.11a
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    • pp.721-725
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    • 1996
  • The microfabricated test structures were used in order to evaluate the stress characteristics in films. The test structures were fabricated using surface micromachining technique, including HF vapor phase etching as an effective release method. The fabricated structures were micro strain gauge, cantilever-type vernier gauge and bridge for stress measurement, and cantilever for stress gradient measurement. The strain was measures by observing the deformation of the structures occurred after release etching and the amount of deformation can be detected by micro vernier gauge, which has gauge resolution of 0.2${\mu}{\textrm}{m}$. The detection principles and the degree of precision for the measured strain were also discussed. The characteristics of residual stress in LPCVD polysilicon films were studied using these test structures. The stress gradient due to the stress variation through the film thickness was calculated by measuring the deflection at the cantilever free end.

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Thermo-mechanical vibration analysis of functionally graded micro/nanoscale beams with porosities based on modified couple stress theory

  • Ebrahimi, Farzad;Mahmoodi, Fateme;Barati, Mohammad Reza
    • Advances in materials Research
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    • v.6 no.3
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    • pp.279-301
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    • 2017
  • Thermo-mechanical vibration characteristics of in homogeneousporous functionally graded (FG) micro/nanobeam subjected to various types of thermal loadings are investigated in the present paper based on modified couple stress theory with consideration of the exact position of neutral axis. The FG micro/nanobeam is modeled via a refined hyperbolic beam theory in which shear deformation effect is verified needless of shear correction factor. A modified power-law distribution which contains porosity volume fraction is used to describe the graded material properties of FG micro/nanobeam. Temperature field has uniform, linear and nonlinear distributions across the thickness. The governing equations and the related boundary conditions are derived by Extended Hamilton's principle and they are solved applying an analytical solution which satisfies various boundary conditions. A comparison study is performed to verify the present formulation with the known data in the literature and a good agreement is observed. The parametric study covered in this paper includes several parameters such as thermal loadings, porosity volume fraction, power-law exponents, slenderness ratio, scale parameter and various boundary conditions on natural frequencies of porous FG micro/nanobeams in detail.

Analysis of Thermal Performance in a Micro Flat Heat Pipe with Axially Trapezoidal Groove (그루브형 마이크로 히트파이프의 열전달특성에 대한 연구)

  • Suh, Jeong-Se
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.360-364
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    • 2001
  • Numerical Aanlysis is made on the thermal performance of micro heat pipe in a axial flat grooved channel. The flow of liquid and vapor is investigated in trapezoidal grooves and the effect of variable shear stress along the interface of the liquid and vapor considered. The results from this study are obtained in the axial variation of pressure difference between vapor and liquid, contact angle, velocity of liquid and vapor and so forth. In addition, maximum heat transport capacity of micro-heat pipe is provided by varying the operation temperature, and compared with that from Schneider and Devos's model in which the interfacial shear stress is neglected.

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