• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.26-30
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• 2003

Since the dimension of cold forged part is larger than the cavity size of forging die, the difference results from the various features, such as, the elastic characteristics of die and workpiece, thermal influences, and machine-elasticity. All of these factors should be considered to get more accurate prediction of the dimension of forged part. In this paper, severe FE techniques are proposed to improve the prediction accuracy of dimension for cold forged part. To validate the importance of the above mentioned factors, and the estimated results are compared with the experimental results. The used model is a closed die upsetting of cylindrical billet. The calculated dimensions are well coincided with .the measured values based on the proposed techniques. The proposed techniques have put two simple but important points into Fe simulation. One is the separation of forging stages into 3 steps, from a loading through punch retraction to ejecting stage. The other is the dimensional change, according to the temperature changes due to the deformation. The FE analysis could predict the dimension of cold forged part within the $10{\mu}m$, based on the more realistic consideration.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.125-134
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• 1990

In order to utilize coal ash, which we go to great expense to scrap, as subba se course material, this study attempts to examine the deformation characteristics of coal ash with the addition of some cement when repeated loads are applied. The material of coal ash is obtained from Young dong and Youngwol thermal power plant. The results are : Unconfined compression strength shows rectilineal increase in propotion to the cement addition ratio. Within the scope of repeated loads of experimental condition, modulus of elasticity tends to decrease while compression strength shows about 21% increase.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.449-465
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• 2017

The aim of the present work is to present a computational study of the non-linear aero-elastic behavior of a multi-layered Thermal Protection System (TPS). The severity of atmospheric re-entry conditions is due to the combination of high temperatures, high pressures and high velocities, and thus the aero-elastic behavior of flexible structures can be difficult to assess. In order to validate the specific computational model and the overall strategy for structural and aerodynamics analyses of flexible structures, the simplified TPS sample tested in the 8' High Temperature Tunnel (HTT) at NASA LaRC has been selected as a baseline for the validation of the present work. The von $K{\acute{a}}rm{\acute{a}}n^{\prime}s$ three dimensional large deflection theory for the structure and a hybrid Raleigh-Ritz-Galerkin approach, combined with the first order Piston Theory to describe the aerodynamic flow, have been used to derive the equations of motion. The paper shows that a good description of the physical behavior of the fabric is possible with the proposed approach. The model is further applied to investigate structural and aero-elastic influence of the number of the layers and the stitching pattern.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.611-633
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• 2020

In this paper, a comprehensive review of nanostructures that exhibit piezoelectric behavior on all mechanical, buckling, vibrational, thermal and electrical properties is presented. It is firstly explained vast application of materials with their piezoelectric property and also introduction of other properties. Initially, more application of material which have piezoelectric property is introduced. Zinc oxide (ZnO), boron nitride (BN) and gallium nitride (GaN) respectively, are more application of piezoelectric materials. The nonlocal elasticity theory and piezoelectric constitutive relations are demonstrated to evaluate problems and analyses. Three different approaches consisting of atomistic modeling, continuum modeling and nano-scale continuum modeling in the investigation atomistic simulation of piezoelectric nanostructures are explained. Focusing on piezoelectric behavior, investigation of analyses is performed on fields of surface and small scale effects, buckling, vibration and wave propagation. Different investigations are available in literature focusing on the synthesis, applications and mechanical behaviors of piezoelectric nanostructures. In the study of vibration behavior, researches are studied on fields of linear and nonlinear, longitudinal and transverse, free and forced vibrations. This paper is intended to provide an introduction of the development of the piezoelectric nanostructures. The key issue is a very good understanding of mechanical and electrical behaviors and characteristics of piezoelectric structures to employ in electromechanical systems.

• Proceedings of the Korean Institute of Building Construction Conference
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• v.y2004m10
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• pp.77-81
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• 2004

The massive structures are not free to move with vibration, differential settlement, thermal stresses because, construction and expansion joint, crack etc., can be large enough to cause leakage as deformation of waterproofing. It has been depended on the test method of tensile/tear strength which is waterproofing performance as behavior of concrete structure crack. However, not to practically confirm the creep applied to concrete surface, even waterproofing membrane have more performance than definite strength and elasticity. Therefore, in this study will focus on the test method to consider a resistance performance about loose adhesion and deformation of waterproofing and behavior of concrete structure as construction/expansion joint, crack. Performance test method on the influence as behavior of concrete structure crack is to choose waterproofing materials and construction method which possible to confront with behavior of 50mm crack in the atmosphere and low temperature. Examine the deformation of waterproofing membrane and loose adhesion which can occur to structure in general job site, suggest standard testing method to analyze correlation waterproofing membrane and structure with 5-types of materials used in this study, such as Adhesion membrane and sheet complex, sheet and urethane complex, self-adhesive sheet, spray poly-urea, spray membrane of rubberized Asphalt.

• The Korean Journal of Community Living Science
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• v.21 no.4
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• pp.551-558
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• 2010

It is a normal circumstance to have high temperature and high humidity in Greenhouses even though these climates are changed by the area, season, climates, the size of the greenhouse, and the crops being raised. Workers in the greenhouses have complained about their uncomfortable work environment and discomfort from the hot conditions, including sunburn. The farmers' ailments are not significantly different between those working in the in greenhouses and those working in the fields. The Farmers' syndrome was almost two times higher for women than those of men for greenhouse workers. This study was developed for functional fatigue clothes for plastic greenhouses which are known for high temperatures and humidity. The ergonomic function and thermal comforts of fatigue clothes were evaluated in the climatic chamber($30.0^{\circ}C$, 70.0%R.H.). The current fatigue clothes which are made of cotton or nylon were purchased at the market. The developed clothes are made of highly absorbent and high speed drying polyester. And these fabrics have excellent elasticity. In this study, the functional fatigue clothes were designed with longsleeved sport shirts and Full length pants. Tre, Tsk, Hcl, HR and the personal subjective sensations such as heat, humidity, and comfortableness were significantly lower when subjects wore the developed clothes made with polyester than the previous attire.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.34-39
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• 2003

Morphing wing sections actuated by piezoceramic actuator LIPCA have been designed and their actuation displacements estimated by using the therml analogy and MSC/NASTRAN based on the linear elasticity. The wing sections are fabricated as the design and tested for evaluation. Measured actuation displacements were larger than the estimated values mainly due to the material non-linearity of the PIT wafer. The morphing wing sections can be used for control surfaces of small scale UAVs or MAVs.

• Journal of the Korean Society of Clothing and Textiles
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• v.27 no.1
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• pp.134-142
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• 2003

Performances of Taekwondo fabrics were evaluated in respect of fiber component. yarn count, weave structure and wearing comfort. As a beginning step, we investigated the present situation of Taekwondo wears by questionnaire from pro and amateur Taekwondo players. Samples employed in this study were cotton/nylon blend fabric that was newly woven for this study as well as fabrics of current Taekwondo wears for sale in the market. Their fundamental properties measured were such as air permeability, water vapor transport. wickability, absorption rate, Qmax values, thermal conductivity, durability, hand value, and etc. In addition, subjective wearing sensations were evaluated using Taekwondo wears made of those fabrics. From the results of the objective measurement and the subjective wearing test, we estimated the total fitness of fabrics as a Taekwondo wear. From the questionnaire we could see that pro players and amateurs wanted highly absorbing, quick drying, and soft-tough and complained abrasive surfaces and static elasticity of current fabrics. In view of the results so far achieved, nylon blended fabrics newly woven in this study, showed better comfort-related properties from both of the objective and subjective tests. It was also represented that finer yams enhanced water absorption and touch, and fabrics with rough surface such as honeycomb weave was superior in wearing comfort as well as aesthetic appearance.

• Structural Engineering and Mechanics
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• v.38 no.2
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• pp.171-193
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• 2011

One of the possible alternatives of simulation-based time-dependent reliability assessment of pre-stressed biconcave and biconvex cable trusses, the Monte Carlo method, is applied in this paper. The influence of an excessive deflection of cable truss (caused by creep of cables and rheologic changes) on its time-dependent serviceability is investigated. Attention is given to the definition of the basic random variables and their statistical functions (basic, mutually dependent random variables such as the pre-stressing forces of the bottom and top cable, structural geometry, the Young's modulus of elasticity of the cables, and the independent variables, such as permanent load, wind, snow and thermal actions). Then, the determination of the response of the cable truss to the loading effects, and the definition of the limiting values considering serviceability of the structure are performed. The potential of the method, using direct Monte Carlo technique for simulation-based time-dependent reliability assessment as a powerful tool, is emphasized. Results obtained by the First order reliability method (FORM) are compared with those obtained by the Monte Carlo simulation technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1988-1992
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• 2011

Polypropylene (PP)-SEBS/silicate composites with PP content of 35, 40, and 45wt% were fabricated by melt compounding at $200^{\circ}C$, using lab scale Brabender mixer. The content of silicate was fixed at 5wt%. The thermal properties of the PP-SEBS/silicate composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). The melting temperature of PP-SEBS compound decreased up to $141^{\circ}C$ with SEBS content. TGA result indicates an increase in degradation temperature when the silicate was added in the PP-SEBS compound. The rheological properties of the compounds were measured by dynamic Rheometer. PP-SEBS/silicate composite indicates higher shear thinning and elastic property than PP-SEBS compound. Van Gurp-Palmen analysis was applied in order to certify an increase in elasticity.