• 한국자동차공학회논문집
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• 제2권4호
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• pp.100-111
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• 1994

Observations on the near-nozzle behavior of an unsteady fuel spray through single cylindrical hole nozzle were made by phase Doopler anemometer and microphotographs. At the edge of the spray, droplet velocity peaked during needle opening and closing. Droplet sizes tended to be small on the edge of spray. The near-nozzle spray angle taken from the microphotographs was time-dependent, even though it increased with gas-to-liquid density ratio as expected. The near-nozzle spray angle was the greatest on the initial stage and decreased to a relatively constant value after about one third of the total injection duration regardless of the ambient gas conditions, even in the near-vaccum condition. The wider near-nozzle spray angle in the early stage is due to the flow characteristics inside the nozzle rather than aerodynamic interactions. However, once the spray was established, aerodynamic interactions are essential in the near-nozzle atomization.

• Steel and Composite Structures
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• 제17권5호
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• pp.641-665
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• 2014

This paper presents the analytical solutions for the size-dependent static analysis of the functionally graded (FG) beams with various boundary conditions based on the nonlocal continuum model. The nonlocal behavior is described by the differential constitutive model of Eringen, which enables to this model to become effective in the analysis and design of nanostructures. The elastic modulus of beam is assumed to vary through the thickness or longitudinal directions according to the power law. The governing equations are derived by using the nonlocal continuum theory incorporated with Euler-Bernoulli beam theory. The explicit solutions are derived for the static behavior of the transversely or axially FG beams with various boundary conditions. The verification of the model is obtained by comparing the current results with previously published works and a good agreement is observed. Numerical results are presented to show the significance of the nonlocal effect, the material distribution profile, the boundary conditions, and the length of beams on the bending behavior of nonlocal FG beams.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.413-417
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• 2004

Recent experiments have shown the 'size effects' in micro/nano scale. But the classical plasticity theories can not predict these size dependent deformation behaviors because their constitutive models have no characteristic material length scale. The Mechanism - based Strain Gradient(MSG) plasticity is proposed to analyze the non-uniform deformation behavior in micro/nano scale. The MSG plasticity is a multi-scale analysis connecting macro-scale deformation of the Statistically Stored Dislocation(SSD) and Geometrically Necessary Dislocation(GND) to the meso-scale deformation using the strain gradient. In this research we present a study of nano-indentation by the MSG plasticity. Using W. D. Nix and H. Gao s model, the analytic solution(including depth dependence of hardness) is obtained for the nano indentation , and furthermore it validated by the experiments.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.205-208
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• 2001

Localized shear band is investigated through the analysis of one-dimensional model for simple shearing deformation of thermally rate dependent material. Generally mesh size or interval of nodes play an important role in determining the overall flow behavior of the material. In order to observe these size effects we adapted non-local theory by including higher order strain gradients of the equivalent strain into the constitutive equation for the flow stress. for the ease of convergence and numerical stability the inplicit finite difference scheme is employed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.322-325
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• 2009

An enhanced continuum model for the size dependent strengthening of particle reinforced composites is presented. The model accounts explicitly for the enhanced strength in a discretely defined "punched zone" around the particle in a metal matrix composite as a result of geometrically necessary dislocations developed through a CTE mismatch. The size of the punched zone presents an intrinsic length scale, and this results in the size dependence of the overall behavior of the composite. Results show that predicted 0.2% offset yield stresses are increasing with smaller inclusions and larger volume fractions and this length-scale effect on the enhanced strength can be observed by explicitly including GND region around the particle.

• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.120-127
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• 2022

Molybdenum disulfide (MoS₂) has been widely used as a catalyst for the bifunctional activities of hydrogen and oxygen evolution reactions (HER and OER). Here, we investigated size dependent HER and OER performance of MoS₂. The smallest size (90 nm) of MoS₂ exhibits the lowest overpotential of -0.28 V at -10 mAcm^-2 and 1.52 V at 300 mAcm^-2 with the smallest Tafel slopes of 151 and 176 mVdec^-1 for HER and OER, respectively, compared to bigger sizes (2 ㎛ and 6 ㎛) of MoS₂. The better HER and OER performance is attributed to high electrochemical active surface area (6 × 10^-4 cm²) with edge sites and low charge transfer resistance (18.1 Ω), confirming that the smaller MoS₂ nanosheets have the better catalytic behavior.

• 대한기계학회논문집
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• 제16권10호
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• pp.1869-1876
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• 1992

본 연구에서는 고온에서 높은 강도특성을 유지하면서 동시에 내마모성이 뛰어 나 가스터어빈의 부재로서의 사용이 기대되는 탄화규소(SiC) 세라믹에 대하여, 고체입 자의 충격에 의해 생기는 손상에 미치는 입자의 재질 및 크기의 영향을 조사하였다. 또 각 형태의 손상발생 임계치와 강도저하에 미치는 입자크기의 영향에 관해서도 검토 하였다.

• 한국정밀공학회지
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• 제13권6호
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• pp.145-151
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• 1996

In sawing operation of cubic zirconia, the performance of diamond cutter blade is very dependent on the blade variables. This investigation presents experimental results which show the effects of the blade variables such as concentration, grain size of diamond, types of diamond abrasives, and bond materials on the behavior of the blades. Based on the experimental results an optimum blade condition for the sawing of cubic zirconia was recommended.

• Steel and Composite Structures
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• 제18권2호
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• pp.425-442
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• 2015

This paper addresses theoretically the bending and buckling behaviors of size-dependent nanobeams made of functionally graded materials (FGMs) including the thickness stretching effect. The size-dependent FGM nanobeam is investigated on the basis of the nonlocal continuum model. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a sinusoidal variation of all displacements through the thickness without using shear correction factor. The material properties of FGM nanobeams are assumed to vary through the thickness according to a power law. The governing equations and the related boundary conditions are derived using the principal of minimum total potential energy. A Navier-type solution is developed for simply-supported boundary conditions, and exact expressions are proposed for the deflections and the buckling load. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and stability responses of the FGM nanobeam are discussed in detail. The study is relevant to nanotechnology deployment in for example aircraft structures.

• Advances in nano research
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• 제13권2호
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• pp.165-174
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• 2022

In the present study, a hybrid model of artificial neural network (ANN) and internet of things (IoT) is proposed to overcome the difficulties in deriving governing equations and numerical solutions of the dynamical behavior of the nano-systems. Nano-structures manifest size-dependent behavior in response to static and dynamic loadings. Nonlocal and length-scale parameters alongside with other geometrical, loading and material parameters are taken as input parameters of an ANN to observe the natural frequency and damping behavior of micro sensors made from nanocomposite material with piezoelectric layers. The behavior of a micro-beam is simulated using famous numerical methods in literature under base vibrations. The ANN was further trained to correlate the output vibrations to the base vibration. Afterwards, using IoT, the electrical potential conducted in the sensors are collected and converted to numerical data in an embedded mini-computer and transferred to a server for further calculations and decision by ANN. The ANN calculates the base vibration behavior with is crucial in mechanical systems. The speed and accuracy of the ANN in determining base excitation behavior are the strengths of this network which could be further employed by engineers and scientists.