아닐링처리에 따른 NbTi초전도 선재의 RRR거동에 미치는 피로손상의 영향

신형섭,오상엽 安東大學校 工業技術硏究所 2000 공업기술연구논문집 Vol.7 No.1

9본으로 구성된 Cu-Ni/NbTi/Cu 복합선재의 RRR에 대한 피로손상의 영향을 연구하기 위하여 상온에서 피로시험을 실시하고, 12K에서 잔류저항을 측정하였다. 피로시험은 아닐링열처리한 초전도 선재를 사용하였다. 피로시험시 소선간의 fretting이 발생한 가능성이 높았지만, 9본 Cu-Ni/NbTi/Cu 복합선재의 피로시험을 통하여 S-N선도를 구살 수 있었다. 피로시험후 NbTi소선의 저항을 측정한 결과, 아닐링한 선재의 RRR값이 처녀재보다 3배가 높았으나, 피로 반복수가 증가함에 따라 격자결함과 Cu안정화재 내부에 전위와 같은 손상의 누적 원인으로 RRR값이 감소하였다. In order to investigate how the fatigue damage influences on the RRR of a 9 strand Cu-Ni/NbTi/Cu composite cable, the fatigue test at room temperature and the residual resistivity measurement test at 12K were carried out. The annealing treated superconducting cable was used in the fatigue test. A conventional S-N curve could be obtained through the fatigue test of the 9 strand Cu-Ni/NbTi/Cu composite cables, despite a high possibility of fretting among strands. From the resistivity measurement of a NbTi strand after fatigue tests, it was found that the RRR for annealed cables was 3 times higher than that for as received one, but with increasing the repeated number the RRR decreased which was resulted from the accumulation of damage such as lattice defects and dislocations within the Cu stabilizer.

소다라임유리에서 구형입자 충격손상에 미치는 가압조건의 영향

신형섭,오상엽 安東大學校 工業技術硏究所 2001 공업기술연구논문집 Vol.8 No.1

가압치구를 이용해 접촉압력을 가할 수 있는 실험장치를 개발하여 가압 구속조건이 구형입자 충격시 발생하는 충격손상의 영향을 조사하였다. 소다라임유리 (33×33×8mm)에 직경3mm인 WC와 Steel구를 각각 30~200m/s의 속도로 충격을 가하였다. 그리고 3가지 다른 조건, 즉 가압치구가 없는 경우, 가압치구가 있으며 압력 p=0㎫, p=200㎫ 를 가한 조건을 설정하였다. 입자충격으로 인하여 ring, radial 등과 같은 균열이 발생되었다. 시험편에 가한 접촉응력이 시험편 내부 응력장을 변화시켰다. 따라서 가압치구가 없는 시험편의 손상영역은 입자충격속도가 증가함에 따라 증가하였다. 200㎫의 접촉압력을 가한 시험편의 경우는 가압치구가 없는 경우에 비해 감소하였다. An experimental investigation was made, which comprise a pressing die, to evaluate the influence of pressing condition on the damage induced by a spherical impact. Steel and WC sphere in 3mm diameter impacted to soda-lime glass specimen with dimension of 33 x 33 x 8mm in the impact velocity range of 30m/s to 200m/s. Three different contact conditions were given for the impact damage evaluation, which are, the cases without pressing die, the cases of p=0㎫ and p=200㎫ with pressing die. The spherical impact had produced various kinds of damage such as ring cracks, cone cracks and radial cracks. The contact pressure applied to the specimen changed stress fields developed in the specimen which suppressed the structural bending of specimen and development of radial cracks. The extent of induced damage in the specimen with contact pressure of 200㎫ was reduced, as compared with the cases of without pressing die or with contact pressure of 100㎫.

Critical Current Degradation Behavior in YBCO Coated Conductors Under Torsional Strain

Hyung-Seop Shin,Dizon, J.R.C.,Tae-Hyung Kim,Dong-Woo Ha,Sang-Soo Oh Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2

<P>The I<SUB>c</SUB> degradation behaviors of a YBCO coated conductor (CC) tape (RABiTS/MOD) was investigated using a sample holder which gives torsional angles to HTS tapes. The I<SUB>c</SUB> degradation in YBCO CC tape under torsional strains occurred gradually which is a characteristic feature under torsion. Uniform torsional deformation was induced in the YBCO CC tape evident from the consistent I<SUB>c</SUB> degradation behavior at each subsection along the longitudinal direction of the tape. Similar with the tension case, the reversible behavior of I<SUB>c</SUB> under torsional loading was found. The irreversible strain, epsiv<SUB>irr.t.</SUB>, was ~0.6%. The critical strain defined by the 95% I<SUB>c</SUB> retention criterion was 1.4% which was located within the irreversible limit. The n-value-thetas behavior in the YBCO CC tape was similar to the I<SUB>c</SUB>/I<SUB>c0</SUB>-thetas behavior.</P>

Critical Current Degradation Behavior in Lap-Jointed Coated Conductor Tapes With IBAD Substrate Under Uniaxial Tension

Hyung-Seop Shin,Dedicatoria, Marlon J,Sang-Soo Oh IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3

<P>Considering the expansion of application field of coated conductor (CC) tapes, it is preferred to adopt IBAD substrate which has high yield strength to resolve the strength problem. The electro-mechanical characteristics of the CC tapes will be influenced by the superconductor type and the deposition process adopted during manufacturing. In this study, the Ic degradation behavior of jointed IBAD processed CC tapes under uniaxial tension has been investigated. The I<SUB>c</SUB> degradation behavior of the jointed CC tapes under uniaxial tension has also been compared with those in single tapes. Differently processed YBCO and SmBCO CC tapes with IBAD substrate have been used as samples. The CC tapes jointed by mechanical controlled method were subjected to uniaxial loading. Joint resistances and critical current of lap-jointed specimens have been derived from the I - V curves obtained at each tensile load at 77 K under self-field. In the case of YBCO CC tapes, lap-jointed tape showed a comparable irreversible strain limit with the single tape.</P>

Bending Strain Characteristics of Critical Current in Double-Layered Bi-2223 Superconducting Tapes

Hyung-Seop Shin,Dizon, J.R.C.,Bonifacio, R.,Sung-Taek Park,Dong-Woo Ha,Sang-Soo Oh IEEE 2008 IEEE transactions on applied superconductivity Vol.18 No.2

<P>The evaluation of reliability of HTS tapes is necessary for practical applications such as magnet, power cables, motors, SMES and HTS coils. The bending strain effect on the critical current, I<SUB>c</SUB>, in multifilamentary Bi-2223 HTS tapes have been investigated. Single and double layered tapes (for high current capacity) were subjected to thermal and pressurization cycles at pressurized liquid nitrogen (LN<SUB>2</SUB>) up to 1 MPa. After the pressurization test, the subsequent occurrence of damage like ballooning due to the diffusion and expansion of LN<SUB>2</SUB> into the tapes were investigated and compared. The Bi-2223 tapes showed different I<SUB>c</SUB> degradation behavior depending upon the geometry and ratio of reinforcement to superconductor adopted.</P>

Analysis of Impact Fracture Behavior in Bulk Amorphous Metals Using Instrumented Impact Testing Apparatus

Shin, Hyung Seop,Kim, Ki Hyun Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.326 No.-

<P>In order to investigate the mechanical behavior of newly developed materials such as bulk amorphous metals, it is essential to use small-size specimens. An instrumented impact testing apparatus was devised which could provide a load-displacement curve on subsize Charpy specimens under impact loading without oscillations. The impact fracture behaviors of Zr-based bulk amorphous metals (BAM) were investigated by using the instrumented impact tester using both V-notched and precracked subsize Charpy specimens. It was found that most of the fracture energy absorbed was used in the process of crack initiation through the development of shear bands.</P>

Review of progress in electromechanical properties of REBCO coated conductors for electric device applications

Shin, Hyung-Seop,Dedicatoria, Marlon The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.4

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes have already been commercialized but still possess some issues in terms of manufacturing cost, anisotropic in-field performance, $I_c$ response to mechanical loads such as delamination, homogeneity of current transport property, and production length. Development on improving its performance properties to meet the needs in practical device applications is underway and simplification of the tape's architecture and manufacturing process are also being considered to enhance the performance-cost ratio. As compared to low temperature superconductors (LTS), high temperature superconductor (HTS) REBCO CC tapes provide a much wider range of operating temperature and a higher critical current density at 4.2 K making it more attractive in magnet and coil applications. The superior properties of the REBCO CC tapes under magnetic field have led to the development of superconducting magnets capable of producing field way above 23.5 T. In order to achieve its optimum performance, the electromechanical properties under different deformation modes and magnetic field should be evaluated for practical device design. This paper gives an overview of the effects of mechanical stress/strain on $I_c$ in HTS CC tapes due to uniaxial tension, bending deformation, transverse load, and including the electrical performance of a CC tape joint which were performed by our group at ANU in the last decade.

Establishment of an easy I_c measurement method of HTS superconducting tapes using clipped voltage taps

Shin, Hyung-Seop,Nisay, Arman,Dedicatoria, Marlon,Sim, KiDeok The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.2

The critical current, $I_c$ of HTS superconducting tapes can be measured by transport or contactless method. Practically, the transport method using the four-probe method is the most common. In this study, a simple test procedure by clipping the voltage lead taps have been introduced instead of soldering which reduces time and effort and thereby achieving a much faster measurement of $I_c$. When using a pair of iron clips, $I_c$ value decreased as compared with the measured one by standard method using soldered voltage taps and varies with the width of the clipped specimen part. However, when using a pure Cu clip, both by clipping and by soldering voltage taps give a comparable result and $I_c$ measured are equal and close to the samples specification. As a result, material to be used as voltage clip should be considered and should not influence the potential voltage between the leads during $I_c$ measurement. Furthermore, the simulation result of magnetic flux during $I_c$ measurement test showed that the decrease of $I_c$ observed in the experiment is due to the magnetic flux density, $B_y$ produced at the clipped part of the sample by the operating current with iron clips attached to the sample.

Comparison of the Bending Strain Effect on Transport Property in Lap- and Butt-Jointed Coated Conductor Tapes

Hyung-Seop Shin,Dedicatoria, Marlon J IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3

<P>Although long-length superconducting wires are now being developed and manufactured, there is still a need for jointing in coil manufacturing and power cables for power distribution which requires miles in length. Therefore, it is important to develop an easy and practical jointing that has an acceptable electrical and mechanical integrity. Depending upon the applications, jointed coated conductor (CC) tapes will experience different stresses and strains during manufacturing and operation that could affect its transport property. Bending strain characterization is necessary since CC tapes are being wound into coils for magnet applications and other electrical devices. In this study, two joint types soldered by mechanical controlled jointing with uniform pressure application have been adopted. Critical currents of the jointed tapes have been measured at 77 K and self field. In the case of easy bending test, a new test procedure has been adopted considering the non-uniform flexural stiffness between jointed and unjointed parts of the sample. Relationship between the critical current and bending strain in easy bending mode has been investigated.</P>

Influence of crystallization on the deformation behavior of Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glass in the supercooled liquid region

Shin, Hyung-Seop,Jeong, Young-Jin,Choi, Ho-Yeon,Inoue, Akihisa Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-

<P><B>Abstract</B></P><P>The deformation behavior of a Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB> (numbers indicate at.%) bulk metallic glass (BMG) under uniaxial tensile loading at different temperatures within the supercooled liquid region was investigated. The variations in the deformation behavior of few material, which resulted from the crystallization induced at low strain rates during testing is discussed. The Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB> BMG showed either homogeneous or inhomogeneous deformation depending on the test conditions of initial strain rate and temperature adopted. It exhibited a maximum elongation of about 560% at the condition of 680K, 5×10<SUP>−4</SUP>s<SUP>−1</SUP>. The increase of the time elapsed during testing at 700 and 720K produced strain hardening due to crystallization at the later part of deformation. The onset of crystallization which occurred during the plastic deformation was accelerated as the initial strain rate increased. X-ray diffraction and hardness results confirmed the influence of the crystallization induced on the deformation behavior of Zr<SUB>55</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB>Cu<SUB>30</SUB> BMG.</P>