• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.273-278
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• 1998

In this paper, basic micro-mechanical properties of unidirectional CFRP composite shell such as bonding strength, fiber volume fraction and void fraction are measured and tensile strength test is performed with a fixture. And then fracture surfaces are observed by SEM. In case of basic micro-mechanical properties, bonding strength is reduce with decreasing of radius of each ply in a shell for the effect of residual stress, fiber volume fraction is smaller than plate, and void fraction is vise versa. For these reason, tensile strength of shell is smaller than plate fabricated with same prepreg. For failure mode shell has many splitted part along its length, and it is assumed that this phenomenon is caused by the difference of bonding strength for residual stress.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.6
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• pp.50-57
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• 2006

The investigation of microscopic precision in high speed endmilling is necessary for machinability evaluation, and the environmentally conscious machining technology have more important position in recent machining process. The microscopic precision of workpiece is influenced by machining environments variation as cutting fluid type and lubricant method. In this study, the cutting forces according to variation of cooling and lubrication are investigated by specially designed tool dynamometer. And the surface roughness, micro hardness and residual stress are evaluated according to machining environment. The characteristics of damaged layer in environmentally conscious machining and conventional machining using cutting fluid are compared experimentally.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.256-259
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• 2008

An micro-probe tip must be manufactured using thin film to evaluate integrity of the semiconductor with narrow distance between pads. In this study, fatigue tests were performed for BeCu thin film which is used in micro-probe tip of semiconductor test machine. The thin film was manufactured by electro plating process, and the specimens were fabricated by wire-cut electric discharge method to make hour glass type specimen of $5000{\mu}m$ width, $29200{\mu}m$ length and $30{\mu}m$ thickness. The fatigue test of load control with 10Hz frequency was performed, in ambient environment. The fatigue cycles were tension-tension with mean stress, at stress ratio, R=0.1.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.333-338
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• 2000

Induction surface hardening is widely used to enhance local strength and hardness. However, most research is only to have a focus on fatigue life and fatigue behavior is not so much studied. So, in this study, Cr-Mo steel alloy(SCM440) was used to show the effect of residual stress and micro hole on the fatigue strength for base metal and induction surface hardened specimen. In addition, the fatigue characteristic between surface hardened and fully hardened steel is somewhat different. It is caused by hardness distribution, residual stress and inclusions etc.. Crack origins are generally micro inclusions for the high strength steel. So, the distribution of inclusions is analyzed statistically.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.397-398
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• 2006

The advanced piezoelectric ceramic composite actuator, which is called LIPCA with the FRP and the optimization of the laminate configuration, was performed to maximize the stress transfer and the fiber bridging effect. This study evaluated the effect of variable electric fields on the PZT characteristic, laminate configuration and fatigue characteristics under the resonance frequency, which meant the largest performance range and the changes of its interlaminar phase were also evaluated by stages. In conclusions, Comparing with the fatigue lift of intact LIPCA, the fatigue life of LIPCA embedded by the artificial delamination was decreased up to 50%. The micro void growth and the coalescence of epoxy were actively made at the interlaminar phase subject to the large tensile stress.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.505-506
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• 2006

Size reduction of micro-aperture using additional deposition is presented in this study. PECVD process was used for additional deposition. Rate of deposition is different with deposition direction because corners of shadowmask membrane have a taper. Deposition into backside showed better than deposition into frontside with size reduction. Shadowmask membrane with two materials has stress because of the difference of a coefficient of thermal expansion The cantilever of membrane bend to opposite direction of deposition. Deposition to both frontside and backside could reduce inside stress.

• Journal of the Korean institute of surface engineering
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• v.43 no.5
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• pp.243-247
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• 2010

The micro Vickers hardness and internal stress of Ni-Fe metal thin film synthesized by electrodeposition method at $25^{\circ}C$ were studied as a function of bath composition, and surface microstructure and atomic compositions of thin films were investigated by SEM and EDS. And the shape change of $200\;{\AA}$ Ni-Fe nanowires made using anodic aluminum oxide(AAO) templates by electrodeposition method were observed by SEM as a function of ultrasonic treatment time and bath composition. The Fe deposition contents on the substrate non-linearly increased with Fe ion concentration over total metal ion concentration. In case of low Fe contents film, the grain size is smaller and denser than high Fe contents deposited films, and the micro Vickers hardness increased with Fe contents of electrodeposited films. These results affected the shape change of nanowire after ultrasonic treatments.

• Structural Engineering and Mechanics
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• v.43 no.5
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• pp.657-678
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• 2012

The mismatch of ply orientations in composite laminates can cause high interlaminar stress concentrations near the free edges. Evaluation of these interlaminar stresses and their role in the progressive damage analysis of laminates is desirable. Recently, the authors developed a new method to relate the physically based micromechanics approach with the meso-scale CDM considering matrix cracking and induced delamination. In this paper, the developed method is applied for the analysis of edge effects in various angle-ply laminates such as $[10/-10]_{2s}$, $[30/-30]_{2s}$ and $[45/-45]_{2s}$ and comparing the results with available traditional CDM and experimental results. It is shown that the obtained stress-strain behaviors of laminates are in good agreement with the available experimental results and even in better agreement than the traditional CDM results. Variations of the stresses and stiffness components through the laminate thickness and near the free edges are also computed and compared with the available CDM results.

• Journal of Fisheries and Marine Sciences Education
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• v.5 no.2
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• pp.128-137
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• 1993

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into buffer layer of turbulent boundary layer on flat plate. The buffer layer of boundary was specified by minus velocity gradient of law of the wall. When the buffer layer region of turbulent boundary layer is filled with micro-bubble of air and viscous of the region is kept low, the velocity profile in the region should be changed substantially. Then the Reynolds stress in the buffer layer region becomes less, which guide to higher velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.8
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• pp.1455-1460
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• 2007

This paper reports the piezoelectric microspeakers that are audible in open air with high quality piezoelectric AlN thin film deposited onto Mo/Ti electrode. This successful achievement, compared to the previous results, is followed by manipulating two material properties: the one is to use a compressively stressed silicon nitride film as a supporting diaphragm (even tensile stressed, around +20 MPa) and the another is to use high quality AlN thin film with compressive residual stress (less than -100 MPa). With these materials, the Sound Pressure Level (SPL) of the fabricated micro speakers shows more than 60 dB from 100 Hz to 15 kHz and the highest SPL is about 100 dB at 9.3 kHz with 20 Vpeak-to-peak sinusoidal input and with 10 mm distances from the fabricated micro speakers to the reference microphone (B&K Type 2669 & 4192L).