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$MgB_2$ bulk의 미세구조와 임계전류밀도에 미치는 polyacrylic acid doping 효과
이승묵,황수민,이창민,주진호,김찬중,Lee, S.M.,Hwang, S.M.,Lee, C.M.,Joo, J.,Kim, C.J. 한국초전도학회 2010 Progress in superconductivity Vol.11 No.2
We fabricated the polyacrylic acid (PAA)-doped $MgB_2$ bulks and characterized their lattice parameters, actual C substitutions, microstructures, and critical properties. The boron (B) powder was mixed with PAA using N,N-dimethylformamide as solvent and then the solution was dried out at $200^{\circ}C$ and crushed. The C treated B powder and magnesium powder were mixed and compacted by uniaxial pressing at 500 MPa, followed by sintering at $900^{\circ}C$ for 1 h in high purity Ar atmosphere. We observed that the PAA doping increased the MgO amount but decreased the grain size, a-axis lattice constant, and critical temperature ($T_c$), which is indicative of the C substitution for B sites in $MgB_2$. In addition, the critical current density ($J_c$) at high magnetic field was significantly improved with increasing PAA addition: at 5 K and 6.6 T, the $J_c$ of 7 wt% PAA-doped sample was $6.39\;{\times}\;10^3\;A/cm^2$ which was approximately 6-fold higher than that of the pure sample ($1.04\;{\times}\;10^3\;A/cm^2$). This improvement was probably due to the C substitution and the refinement of grain size by PAA doping, suggesting that PAA is an effective dopant in improving $J_c$(B) performance of $MgB_2$.
샌드위치 구조를 가지는 복합재의 손실계수 향상을 위한 설계
이창민(C. M. Lee),전관수(G. S. Jeon),강동석(D. S. Kang),김병준(B. J. Kim),김종훈(J. H. Kim),강명환(M. H. Kang),서영수(Y. S. Seo) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.3
Underwater weapon system is required to structurally strong material, since as it is directly exposed to external shock. It should also be using the lightweight material in order to take advantage of buoyancy. Composite materials meet these requirements simultaneously. Particularly in the case of submarine, composite materials are widely used. It is important to have a high strength enough to be able to withstand external shock, but it is also important to attenuate it. In a method for the shock damping, viscoelastic damping materials are inserted between the high strength composite material as a sandwich structure. Shock attenuation can be evaluated in the loss factor. In ASTM(American Society of Testing Materials), evaluation method of the loss factor of cantilever specimens is specified. In this paper, mode tests of the cantilever are performed by the ASTM standard, in order to calculate the loss factor of the viscoelastic damping material by the specified expression. Further, for verifying of the calculated loss factor, mode test of compound beams is carried out. In addition, the characteristics of the material were analyzed the effect on the loss factor.
이창민(C.M. Lee),신영훈(Y.H. Shin),이기선(K.S. Lee) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Rocket, held using the CCA for the mission, a plurality of recording devices, and navigation equipment. In case of a projectile which is entered the water after fired into the air, after performing stages and fairing separated in flight to enter the underwater. It is caused by the explosion of gunpowder mainly, vibration phenomenon of a large transition is induced structurally very, also on entering the water, have a significant shock structurally separated. If shock is transmitted directly to the CCA through the body, it can be caused malfunction of payloads, resulting in failure of the mission of the projectile. In order to ensure the stability against shock and apply the insulation system, mainly to amplify the vibration of the payloads, and is vulnerable to environmental vibrations excessive low frequency region. Therefore, in this paper, target resonance frequency is calculated using the relative displacement and allowable relative displacement of CCA to excitation for improved shock resistance ultimately.