• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.30-33
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• 2009

본 논문에서는 형상기억합금의 특징적인 거동을 모사하기위한 구성방정식을 제안한다. 제안되는 구성방정식은 기존의 소성모델을 기초로 하는 현상학적인 모델로, 소성 경화이론에서 사용되는 항복곡면에 대응되는 상변이 곡면을 정의하여 형상기억합금의 비선형 거동을 모사한다. 단, 상변이 곡면이 1개만 존재하는 소성모델과는 다르게, 오스테나이트에서 마르텐사이트로의 정방향 상변이와 마르텐사이트에서 오스테나이트로의 역방향 상변이를 각각 해석하기위해 독립적인 2개의 상변이 곡면을 정의해주게 된다. 기계적 하중만이 아닌 열적 하중의 변화에도 비선형 거동을 보이는 형상기억합금의 특성을 반영하기위해 상변이 곡면은 응력과 온도의 함수로 정의되며, 이렇게 정의된 상변이 곡면을 바탕으로 리턴 매핑 알고리즘을 적용하여 열적하중과 기계적하중의 변화에 따른 형상기억합금의 거동을 모사하는 구성방정식을 제안하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.490-495
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• 2001

This paper deals with an analysis and countermeasure for improving the shock performance of laptop computers. The shock analysis is carried out by using the commercial program of LS-DYNA3D. Also the analysis is verified by the measurements from modal tests and shock tests. The available countermeasures are investigated theoretically and experimentally to find the effective methods of reducing the shock acceleration on hard disk driver during one side fall test. The hard disk drive is the most sensitive part in a laptop computer. This research shows the effects of the spring constant of rubber pad, the reinforcement of mechanical parts and the location of a hard disk driver, on the shock reduction.

• Journal of Welding and Joining
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• v.12 no.4
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• pp.151-161
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• 1994

FCAW has wide application in ship fabrication, maintenance and field erection. It has many advantages over SMAW.SAW and GMAW process. In many applications, the FCAW provides highquality weld metal. This method can reduce weld defects especially porosity and spatter. But the fatigue characteristics of those deposited metal have been rarely investigated. The purpose of this study is to investigate the cyclic stress-strain behavior and fatigue tests by the constant strain control were carried out on the rounded smooth specimen with deposited metal using the metal type flux cored wire. As the results of this study for the deposited metal welded by the metal type flux cored wire, the hardening or softening characteristics under cyclic load were investigated and cyclic stress-strain curve, strain-fatigue life curve, stress-strain function and fatigue life relation which are useful to estimate the fatigue life under the stress concentration condition were obtained.

• Transactions of Materials Processing
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• v.25 no.3
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• pp.189-194
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• 2016

In the current study, spring-back of DP980 steel sheet was numerically evaluated for U-bending using a yield function with a hardening model. For spring-back prediction, two types of yield functions - Hill'48 and Yld2000-2d - were considered. Additionally, isotropic hardening and the Yoshida-Uemori model were used to investigate the spring-back behavior. The parameters for each model were obtained from uniaxial tension, uniaxial tension-compression, uniaxial tension-unloading and hydraulic bulging tests. The numerical simulations were performed using the commercial software, PAM-STAMP 2G. The results were compared with experimental data from a U-bending process.

• Journal for History of Mathematics
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• v.29 no.2
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• pp.103-143
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• 2016

We study the topics of the lectures in Analysis in 19th century at Ecole Polytechnique of France through the lists of the contents of the Cours d'Analyse by Cauchy, Sturm and Jordan, respectively and also we show how they stated the definitions of functions, continuity and limits in their Cours d'Analyse. Through this, we see that in 19th century, in France, analysis included differential and integral calculus, differential equations, variations and applications of these to differential geometry, and it was far from today's mathematical analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.961-966
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• 2001

The schematic design process is formulated to develop the vibroisolating rubber mount in optical disc drives. The dynamic model of vibration isolation system is established by using a rigid body with 6 degree of freedom and linear springs with damping property. Considering the practical vibration condition of DVDP(Digital Versatile Disk Player), the required properties of vibroisolating rubber mounts are investigated. Also finite element model of a vibroisolating rubber mount is used to obtain shape design concept and identify the characteristics of a rubber mount which satisfies the required properties from previous design stage. Finally the evaluation method of dynamic properties of vibroisolating rubber mounts is established by utilizing modal test method. Based on the developed process, vibroisolating rubber mounts with a good performance have been developed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.586-591
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• 2001

Dynamic analysis using impulse responses is formulated to estimate effect of slider rail shape on dynamic responses. Impulse responses are obtained on numerical nonlinear model including rigid motion of slider and fluid motion of air bearing under the slider. Dynamic characteristics of slider motion are evaluated by utilizing the decay ratio of impulse responses and modal frequencies from frequency response functions. The dynamic characteristics of the developed NFR(Near Field Recording) slider are checked by comparing those of HDD sider(Nutcracker). Also, sensitivities of slider position conditions and rotation speed on the dynamic characteristics are investigated. The researches show that the utilized method is a good indicator of designing the better slider.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.737-741
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• 2000

Portable communication devices such as laptop computers suffer impact-induced failure in their usage. Drop/impact performance of these products is one of important concerns of product design. Because of the small size of this kind of electronics products, it is very expensive, time-consuming and difficult to conduct drop tests to directly detect the failure mechanism and identify their drop behaviors. Finite element analysis provides a vital, powerful vehicle to solve the problems. The models are created with HYPERMESH, and the analysis is carried out with LS-DYNA3D. The analysis is focused on HDD impact behavior in acceleration peak values.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.221-229
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• 1992

A series of experiments on the resuspension of deposited fine-grained sediments were carried out in a recirculating straight flume to investigate the influence of the sediment type, water content and bed shear stress (${\tau}_b$) on the resuspension characteristics of the sediments. The sediments were sampled from Youngkwang coast and Youngdo coast which are located in the western sea and southeastern sea of Korea, respectively. Critical bed shear stress (${\tau}_c$) for resuspension was deduced for each experimental series. For the same sediment, critical bed shear stress for resuspension decreased but suspension mass or rate increased with increasing water content. The resuspension of deposited fine-grained sediments depended strongly on the water content, and the sediment type characterizing the inter-particle bond strength. It has been found that critical bed shear stress for resuspension in the unidirection flow is about 4 times higher than that in the combined wave-current flow, In case of lower bed shear stress, after an initially high suspension, suspension mass approaches a constant value due to the bed hardening with increasing time, but in case of higher bed shear stress, suspension mass increased successively due to the bed softening with time. Initial suspension rate, $E={\alpha}_3({\tau}_b/{\tau}_c-1)^{\beta}$ (where ${\alpha}_3$ and ${\beta}$=empirical constants), was estimated for each experimental series, ${\alpha}_3$ and ${\beta}$ values for the same sediment increased with water content.

• Journal of the Korea Institute of Building Construction
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• v.14 no.1
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• pp.110-117
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• 2014

The objective of this study is to investigate an effect of curing temperature on autogenous shrinkage of high strength cement mortar with 0.15 of W/B incorporating fly ash and silica fume in terms of equivalent age. The contents of fly ash and silica fume are varied from 10% to 30%. Non linear regression model applying equivalent age was used to estimate the autogenous shrinkage evolution. To obtain apparent activation energy($E_a$), setting time method by Pinto and existing method were calculated and compared respectively. Test results showed that use of silica fume increased autogenous shrinkage while use of fly ash decreased it. It was also found that poor agreements were obtained when $E_a$ by setting time was applied. But, application of existing $E_a$ resulted in a good agreement between calculated autogenous shrinkage and measured one.