• Transactions of Materials Processing
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• v.31 no.3
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• pp.136-142
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• 2022

The purpose of this study was to investigate the effects of sample thickness and support structure on the residual stress of Hastelloy X superalloy samples fabricated by laser powder bed fusion (LPBF), which is an additive manufacturing process. The residual stresses of LPBF samples with different thicknesses and support structures were measured using X-ray diffraction. The results revealed that as the thickness of sample increased from 2.5 mm to 20 mm, its tensile residual stress gradually decreased from 443.5 MPa to 182.2 MPa. Additionally, the residual stress in the bottom region of sample was higher than that in the top region, and the residual stress difference in the bottom and top regions became more pronounced as the sample thickness decreased. The residual stress of LPBF sample also varied depending on the structure of support. The residual stress of sample decreased with increasing contract area between the sample and the support, because the larger contract area led to smaller temperature gradient throughout the sample.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.1
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• pp.7-11
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• 2020

Carbon solubility on the paste deposition methods in the carbon-doped TiZrN coating was investigated in terms of lattice distortion and atomic concentration. After depositing the carbon paste by the dip coating, spin coating and screen printing, the laser was ablated to form the carbon gradient layer. Thickness and the concentration of doped carbon depended on the paste deposition method. Crystal structure analysis indicated that more lattice distortion occurred when coating layers were doped with spin coating and screen printing than when coating layers were doped with dip coating. The XPS depth profile showed that the thickness of carbon gradient layer by dip coating was about 30 nm, spin coating and screen printing are approximately 100 nm, formed more gradient layer. The hardness before laser carburization was about 30 GPa, and the hardness of 31 GPa with dip coating and 37 GPa with spin coating and screen printing. It was indicated that paste deposition methods for laser carburization contributed to lattice distortion and gradient layer.

• Korean Journal of Optics and Photonics
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• v.18 no.4
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• pp.256-263
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• 2007

High NA objective design by using SELFOC materials was studied, and two kinds of objective for optical pick-up were designed. The SELFOC materials have radial gradient index distribution, and it gives additional degree of freedom in optical design. Therefore, we expect that optical design of high NA objective without aspheric surface will be possible. In this study, the variation of ms spot diameter was investigated as a function of quadratic constant and refractive index on axis for various combinations of axial thickness and entrance pupil diameter. For the survey, Code V was used for optimization and evaluation of the objective lenses. The result suggested that larger quadratic constant and higher refractive index on axis could give us better imaging performance for all combinations of axial thickness and pupil diameter. Based on the survey, we designed high NA objectives for DVR. There were two kinds of design solution consisting two spherical SELFOC lenses. The solution I had positive-positive lens configuration with short over-all-length, but it had poor off-axial performance compared with the solution II. The solution II had negative-positive lens configuration with good off-axial imaging performance. But the solution II had some disadvantages, long over-all-length and large diameter of the second lens.

• Journal of Acupuncture Research
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• v.21 no.4
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• pp.31-51
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• 2004

Objective: The propose of this study is to investigate the characteristics of combustion in indirect moxibustion with garlic. Methods: We observed the characteristics of combustion by the variations of the thickness(3mm, 4mm, 5mm) of a slice for indirect moxibustion with garlic and mass(80mg, 100mg, 120mg) of moxa cone and existence of holes. The temperature of indirect moxibustion for garlic insulation with holes was higher than temperature of indirect moxibustion for garlic insulation without holes. Combustions time in the preheating period is about 1 minute, it varies by the existence of holes, the thickness of a slice for indirect moxibustion with garlic, and the density of moxa cone. Results: Maximum temperature of heating period was $38.7{\sim}46.2^{\circ}C$, combustion time in the heating period was 118~164sec and maximum ascending temperature gradient was $0.102{\sim}0.264^{\circ}C/sec$. Retaining period was shorter than heating period and stimulus of heating retains more, because it is higher than body temperature. By this report, indirect moxibustion with garlic is more effective with holes and the appropriate thickness of a slice for indirect moxibustion with garlic is 3.5~4mm. It is appropriate that the diameter of moxa cone is 8mm and height of that is 10mm. With this condition, effective combustion period is 120sec, maximum temperature is $42{\sim}44^{\circ}C$, maximum ascending temperature gradient is $0.14{\sim}0.16^{\circ}C/sec$. It is necessary to study clinical correlations for more accurate quantitative standard.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.206-213
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• 2013

Transient response of a crack in a functionally graded piezoelectric material (FGPM) interface layer between two dissimilar homogeneous piezoelectric layers under anti-plane shear is analyzed using integral transform approaches. The properties of the FGPM layer vary continuously along the thickness. Laplace and Fourier transforms are used to reduce the problem to two sets of dual integral equations, which are then expressed to the Fredholm integral equations of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGPM to show the effects on electric loading, gradient of the material properties, and thickness of the layers. Computed results yield following conclusions: (a) the DERR increases with the increase of the gradient of the material properties of the FGPM layer; (b) certain direction and magnitude of the electric impact loading impedes crack extension; (c) increase of the thickness of the FGPM layer and the homogeneous piezoelectric layer which has larger material properties than those of the crack plane are beneficial to increase of the resistance of transient fracture of the FGPM layer.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.3
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• pp.3477-3491
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• 1974

Following are the results of the study on the property of falling permeation of stratified soil in the close state under existence of stagnant water on a soil layer. 1. When on the stratified soil a least permeating layer was put on the soil layer the load Pressure was present owing to appearance of saturation close state driving decrease of the pressure in the lower layer, on the other hand when the least permeating layer was placed under the layer the lower least permeating layer pressure was decreased. 2. In the case of least permeating layer the variation of current gradient according to the respective level after treating the layer was enormous and due to usal storage phenomena for the Kl layer which was coarse that was trifle. 3. The permeability of the respective layer of stratified soil in the close state died not always coincide with that of single layer. 4. Generally Zunker's equation of average permeability was valid but actually calculated permeating velocity after treating the layer of stratified soil was seriously differ from the measured value owing to the variation of current gradient, especially when the pressure head at the layer boundany was discontinuous the validity of the equation of average permeability was seemed to be doubtful. 5. The permeating velocity of stratified soil was regulated by the least permeating layer, i.e. it is thought to be rational to estimate the value by calculating the current gradient with its proper permeability, pressure headon the layer and its thickness.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1712-1721
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• 2004

A method of measuring the thermal diffusivity of semi-infinite solid material at room temperature using photothermal displacement is proposed. In previous works, within the constant thickness of material, the thermal diffusivity was determined by the magnitude and phase of deformation gradient as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of parameters, such as, radius and modulation frequency of the pump beam and the thermal diffusivity, was studied. We propose a simple analysis method based on the zero -crossing position of real part of deformation gradient and the minimum position of phase as the relative position between two beams. It is independent of parameters such as power of pump beam, absorption coefficient, reflectivity, Poisson's ratio, and thermal expansion coefficient.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.403-413
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• 1985

Hot-wire measurements of second and third-order mean products of velocity fluctuations have been made in the separated, reattached, and redeveloping boundary layer behind a vertical fence. Mean velocity, wall static pressure distributions have also been measured in the whole flow field. Upstream of the reattachment point, the separated shear layer developes as a free mixing layer, but the gradient of the maximum slope thickness, turbulent intensities and the Reynolds shear stress are higher than that of the mixing layer due to initial streamline curvature and the effects of highly turbulent recirculating flow region. In the reattachment region, Reynolds shear stress and triple products near the surface is far more rapid than the decrease of the shear stress; that is the presence of the solid wall has a marked effect on the apparent gradient diffusivity of intensity or shear stress and throws doubts upon the usefulness of the simple gradient diffusivity model in this region.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.4 no.2
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• pp.155-160
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• 2004

In this paper, we describe the results of a study on the edge enhancement of X-ray images by using their fuzzy system representation. A set of gray scale X-ray images was generated using the EGS4 computer code. An aluminum plate or a lead plate with three parallel strips taken out has been used as the object with the thickness and the width of the plate, and the gap between the two strips varied. We started with a comparative study on a set of the fuzzy sets for their applicability as the input fuzzy sets for the fuzzy system representation of the gray scale images. Then we describe how the fuzzy system is used to sharpen the edges. Our algorithm is based on adding the magnitude of the gradient not to the pixel value of concern but rather to the nearest neighboring pixel in the direction of the gradient. We show that this algorithm is better in maintaining the spatial resolution of the original image after the edge enhancement.