• E2M - 전기 전자와 첨단 소재
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• 제10권3호
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• pp.239-246
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• 1997

The ZnO is stabilize dielectric constant over a broad temperature range because its addition makes the relaxation time short. In this study, the composite oxide material (B $a_{0.85}$ $Ca_{0.15}$)Ti $O_{3}$ was mixed by ZnO additive material and the dielectric polarization characteristics was studied. The relative density was over 90[%] at all specimen in the structural characteristics. Among of the specimen, the relative density of (B $a_{0.85}$ $Ca_{0.15}$)Ti $O_{3}$ with ZnO (0.4mol) has a 95[%]. The grain size of composite oxide material with an increasing ZnO increased and it was 1.0[.mu.m]-1.22[.mu.m]. In the electrical characteristics, the charge and discharge current was increased by ZnO addition. The dielectric relaxation time was increased by space charge polarization at above 110[.deg. C] and the dielectric relaxation time was fixed by space charge polarization of para-dielectric layer at below 110[.deg. C]. The dielectric relaxation time was maximum when the grain size was small. The dielectric relaxation time is decreased with an additive material ZnO and interface polarization, existing void at the grain and grain boundary. The remnant polarization is increased and the coercive electric field is decreased by ZnO.

• 한국구조물진단유지관리공학회 논문집
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• 제20권4호
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• pp.94-103
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• 2016

궤도가 역사의 상부에 위치하여 열차운행으로 인하여 발생한 진동이 직접 전달되는 선하역사에서 구조물 진동과 이로 인한 구조물기인 소음이 기준치보다 높은 것으로 나타남에 따라, 기존 선하역사에 대하여 열차 운행의 중단 없이 진동저감이 가능한 경제적, 효율적 방안이 요구된다. 이에 본 연구에서는 진동전달 경로상의 기둥에 워터젯 공법으로 기둥단면에서 피복재 부분을 파쇄한 후 진동전달 절연기능을 가지는 에폭시 소재의 방진재를 보강하여 진동을 저감시키기 위한 구조진동절연시스템을 개발하였다. 방진재의 보강체적을 변수로 한 진동절연 시스템을 실제역사 기둥의 1/4축소모형에 적용하고, 충격가진 시험을 통한 진동저감 성능과 횡하중 반복가력시험을 통한 구조적 성능을 검증하고자 하였다. 충격가진 실험결과로부터 구조진동절연시스템을 적용할 경우 고유 진동주기가 하향되어 진동응답 특성이 변화되고 감쇠비는 약 15~30%까지 증가를 나타내어 진동저감 성능이 있음을 알 수 있었다. 또한 반복하중 가력에 의한 구조성능 실험에서 하중-변위 및 강성변화에 대한 고찰과 연성도 및 에너지 소산의 증가를 보인 결과로 부터 구조부재로의 기능을 유지함을 확인 할 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.269-272
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• 2005

Epoxy resins are gradually becoming some of the most important and versatile polymers in modem civil engineering. Because epoxy resins have some unigue properties, such as toughness, versatility of viscosity and curing conditions, good handling characteristics, high adhesive strength, inertness, low shrinkage compared to most other thermo-setting resins and concrete, and resistance to chemicals, they have found many applications in construction castings, repair materials, road or bridge deck pavements, coatings, and as structural or non structural adhesives. In this applications, epoxy resins are widely used for polymer concretes, grouting materials, injection glues, and sealants. In this paper, characteristics of deformation of repair material after repaired have been investigated by viscosity of repair material and the width of crack. It is believed that flexural strength of epoxy resin with low viscosity is high because tensile strength is high and elongation at break is low, fracture energy is low.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.569-576
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• 2003

Fundamental issues in static finite element analysis of reinforced concrete panel subjected to biaxial tensile loads are discussed. This paper is trying to bring our attention to the appropriate use of concrete material models such as cracking criteria, tension stiffening model and the steel models which are basically used in the nonlinear finite element analysis of reinforced concrete panels. We mainly investigate the sensitivity of available material models and finite element technologies to the finite element analysis result using our recent reinforced concrete panel experiment result. Throughout this study, we found that the judicious use of the material models and finite element technologies with the sound understanding of structural characteristics can only guarantee the accurate prediction of panel behaviour.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.159-163
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• 1999

A seat frame structure in automotive vehicles made of polymer matrix composite to achieve weight reduction at low cost was developed. In order to design and manufacture the actual product, studies on material selection, and structural analyses were performed. Structural analyses were performed with a finite element analysis. Analyses were done for several cases suggested in various safety regulations of FMVSS(Federal Motor Vehicle Safety Standards). Each result was utilized to modify the actual shape to obtain a lighter, safer and more stable design. The final design was used to produce a sample bottom plate of the seat structure. Substitution of the material resulted in a weight reduction effect with equivalent strength, fatigue and impact characteristics. Furthermore, several effects from the replacement of the material besides weight reduction were also examined.

• 한국공작기계학회논문집
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• 제17권3호
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• pp.34-39
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• 2008

In this study, CFRP(Carbon Fiber Reinforced Plastics) that has high specific strength and elastic modulus and low thermal strain was used as a material for the lightweight structural member. CFRP is a fiber material as anisotropic material. The anisotropic material is characterized by the change of its mechanical properties according to stacking orientation angle. CFRP orientation angle was oriented in [A/B]s in order to examine the effect of CFRP orientation angle on the characteristics of energy absorption. CFRP is very weak to the impact from the outside. So, when impact is applied to CFRP, its strength is rapidly lowered. The hybrid material was manufactured by combining CFRP to aluminum which is lightweight and widely used for structural members of the automobile. The hybrid member was shaped as a side member that could support the automobile engine and mount and absorb a large amount of impact energy at the front-end in case of automobile collision. The bending test device was manufactured in accordance with ASTM standard, and mounted to UTM for bending test. For comparing bending characteristics of the hybrid member with those of Aluminum and CFRP member, tests were performed for aluminum, CFRP and hybrid member, respectively.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.275-278
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• 소성∙가공
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• 제14권6호
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.111-118
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• 2006

The elastic buckling strength of a corrugated culvert made of orthotropic material such as FRP was evaluated. The height and length of a corrugated wave and the thickness of the culvert were considered as factors affecting the buckling strength of the culvert. And also, the ratio of the longitudinal stiffness and transverse stiffness was considered as the parameter affecting on the buckling strength of the used orthotropic material. Buckling strengths of various corrugated culvert models with different shapes and stiffness ratio were evaluated by FE analyses and a formula to estimate the elastic buckling strength was suggested from the regression with FE analysis results. Analysis results show that a corrugated culvert has superior buckling strength to a general flat pipe and the suggested formula estimates accurate buckling strength of the corrugated culverts made of orthotropic material.

• 항공우주시스템공학회지
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• 제10권1호
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• pp.103-110
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• 2016

This study shows the statistical properties of the domestic composite material prepregs test result. During the last three years(2012.5~2015.6) the prepreg specimen tests have been performed by referring to NCAMP developed test procedure which was approved by FAA. The database of (1) Carbon Tape, (2) Glass Fabric, and (3) Carbon Fabric composite material prepregs' characteristics have been established for certified aircraft structures. This qualified materials can be used for aircraft structural design through proper material equivalency procedures.