• Tribology and Lubricants
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• 제19권2호
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• pp.102-108
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• 2003

The height of laser bumps has been considered as the limit of the minimum flying height in the contact start-stop (CSS) of hard disk drives. In this paper, tribological interactions at flying height under laser bumps are investigated in a spin stand for development of ultra-low flying head-disk interface. With the reduction of the spinning speed in a spin stand, the flying height is decreased under the height of laser bumps and, then, head-disk interactions are investigated using AE and stiction/friction signals. During seek tests and 20000 cycle-sweep tests, AE and stiction/friction signals are not significantly changed and there are no catastrophic failures of head-disk interface. Bearing analysis and AFM analysis show that there are signs of wear and plastic deformation on the disks. It is suggested that flying height could be as low as and, sometimes, lower than laser bump height.

• 소성∙가공
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• 제13권3호
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• pp.230-235
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• 2004

A new design based on the appropriate geometry of molded part and type of runner system under the optimal processing conditions was proposed to minimize the micro weld lines on the sub deco surface molded by two shot molding. Theoretical and experimental studies were conducted to examine the cause of the weld lines during the overmolding process in two shot molding. Various dimensions and geometries of substrate$(1^{st}shot)$ and the wall thickness of overmold$(2^{nd}shot)$ have been proposed to avoid the weld lines which are the most inevitable appearance defects occurred on the sub deco. The each design proposal was analyzed by mold flow analysis after part modeling. The analysis results were compared with molded part from mass production tool. It could be seen that from the analysis that the proper geometry of plastic part and type of runner system considering pressure drop under the optimal processing conditions were the most influential factors to avoid weld lines occured on the sub deco.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1125-1128
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• 2007

The laminating technique for developing flexible liquid crystal display was demonstrated by using a thin UV curable polymer film and a plastic substrate with patterned polymer wall structure. We adopted the rigid wall structure to provide a solid mechanical support for the stable molecular alignment of liquid crystals (LCs) in the device. The cover film was prepared to have an ability of aligning LC molecules by patterning a micro-groove structure using the soft-lithographic process. These two substrates can be assembled tightly by the laminating and one-step UV irradiation process because of the adhesive nature of the used UV curable polymers. Proposed method can be used to fabricate the flexible LC display with simplicity and also be applicable for a cost-effective roll-to-roll process.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년 추계학술발표대회 개요집
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• pp.109-111
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• 2006

In this study, microstructure and mechanical properties for the friction stir welded 2519Al-T87 alloy of the thickness of 38.8mm were studied using DSC, OM, SEM and micro hardness tester. DSC analysis show that GP Zone, ${\theta}'$ and $\theta$ phases in upper part and ${\theta}'$ and $\theta$ phase in lower part of the FSW zone. Recrystallized large grains are observed in HAZ, and elongated small and large grain in the TMAZ. In SZ, very small grains forms by high plastic deformation and heat from friction by tool and specimen.

• 소성∙가공
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• 제3권2호
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• pp.229-242
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• 1994

An approximate procedure based on a combination micro-macroscopic theories of plasticity for predicting the crystallographic texture during the plane strain forming of fcc metals has been developed. This procedure is divided into two steps. Firstly, we extract the history of the deformation gradient at all deformed elements with a elasto-plastic finite element method using isotropic plasticity model. Secondly, we use this deformation gradient history to predict the crystallographic deformation texture based on the Bishop-Hill theory. Renouard and Wintenberger' method is chosen for selecting the active slip systems. The predicted results have been compared with reported experimental results. The calculated results are in good agreement with their results.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권2호
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• pp.45-55
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• 2007

In this study, two types of fatigue tests were conducted. Firs, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. Creep deformation was dominant in thermal fatigue and plastic deformation was main parameter for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• 소성∙가공
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• 제16권5호통권95호
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• pp.406-411
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• 2007

The microstructure and the hardness of interstitial free steel processed by equal channel angular pressing (ECAP) was investigated experimentally. ECAP processing of route A and route C was compared with regard to grain refinement by transmission electron micrographs. Micro hardness evolution was correlated with the gram structure produced by ECAP. Especially, the effects of the ECAP processing temperature and the number of processing passes were discussed in terms of grain refinement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.547-548
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• 2009

분산제 코팅 및 단일형상을 가진 폴리아미드 섬유보강 콘크리트 기술을 적용하여 160MPa 초고강도 콘크리트의 내화성능을 평가한 결과, 콘크리트의 압송성능을 개선했을 뿐만 아니라 콘크리트의 내화성능 관리기준을 만족하였다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.564-568
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• 2006

Smooth picture module is operated by vibration to tilt the light from the DMD (digital micro mirror device) of DLP projection TV, which makes the screen of the TV smoother and DMD chip cost lower. To satisfy the vibration characteristics of smooth picture module, it is designed by optimizing moment of inertia, spring constant and damping coefficient, using structural and fluid dynamic simulation that showed a good agreement with experimental data. To reduce the material cost and moment of inertia, engineering plastic is used and the reliability is estimated. A VCM (voice coil motor) type actuator for smooth picture has to satisfy performance requirements such as higher driving force, lower power consumption, and lower cost. The initial design and optimization for VCM was performed using FE analysis. It allowed us to optimize the design of magnetic circuit of the proposed actuator to obtain higher force while maintaining a lower cost.

• 한국정밀공학회지
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• 제15권5호
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• pp.167-175
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• 1998

A mathematical formulation is presented to model anisotropy from the deformation textures developed in a forming process. In this work, a micro-mechanical-based polycrystalline analysis is implemented into a consistent finite element method for the anisotropic, viscoplastic deformation of polycrystalline metals. As suggested by Taylor, the deformation of each grain in an aggregate is assumed to be same as the macroscopic deformation of an aggregate or a macro-continuum point. Algorithms are developed to represent the plastic anisotropy, such as the anisotropic yield surface and R-value, from the predicted deformation texture. As applications, the evolution of texture in rolling, upsetting and drawing/extrusion processes are simulated and the corresponding changes of mechanical properties such as yield surface and R-value are predicted.