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Delamination Characteristics in Wide REBCO Coated Conductor Tapes Under Transverse Loading
Gorospe, Alking,Dedicatoria, Marlon J.,Hyung-Seop Shin Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>Superior characteristics and great potential of coated conductor (CC) tapes are some of the promises in pursuit of energy efficient application in electrical field. However, in electric device applications, the coefficient of thermal expansion (CTE) mismatch of each constituent layer, screening current, excessive radial tensile stresses during operation, and other coil fabrication related reasons might cause delamination damage in CC tapes. It was reported that the delamination among its constituent layers resulted to the degradation of its electromechanical properties on coil application. Therefore, the investigation on its delamination behavior is necessary for device application design. In this study, using the anvil test method, the delamination behaviors in 12-mm-wide Cu stabilized and brass laminated GdBa<SUB>2</SUB>Cu<SUB>3</SUB>Oy CC tapes with stainless steel substrate were investigated. The mechanical delamination strength of the CC tapes for differently assembled upper anvil and CC tape configurations about widthwise direction was investigated by using a 4 mm × 8 mm size upper anvil. Mechanical delamination strength of the CC tape was not enhanced by the addition of brass laminate and showed no significant difference depending on the superconducting side or the substrate side. Furthermore, both CC tapes exhibited similar delamination mechanisms and sites but showed different fracture morphologies.</P>
Delamination behaviors of GdBCO CC tapes under different transverse loading conditions
Gorospe, Alking B.,Bautista, Zhierwinjay M.,Shin, Hyung-Seop The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.3
In superconducting coil applications particularly in wet wound coils, coated conductor (CC) tapes are subjected to different type of stresses. These include hoop stress acting along the length of the CC tape and the Lorentz force acting perpendicular to the CC tape's surface. Since the latter is commonly associated with delamination problem of multi-layered CC tapes, more understanding and attention on the delamination phenomena induced in the case of coil applications are needed. Difference on the coefficient of thermal expansion (CTE) of each constituent layer of the CC tape, the bobbin, and the impregnating materials is the main causes of delamination in CC tapes when subjected to thermal cycling. The CC tape might also experience cyclic loading due to the energizing scheme (on - off) during operation. In the design of degradation-free superconducting coils, therefore, characterization of the delamination behaviors including mechanism and strength in REBCO CC tapes becomes critical. In this study, transverse tensile tests were conducted under different loading conditions using different size of upper anvils on the GdBCO CC tapes. The mechanical and electromechanical delamination strength behaviors of the CC tapes under transverse tensile loading were examined and a two-parameter Weibull distribution analysis was conducted in statistical aspects. As a result, the CC tape showed similar range of mechanical delamination strength regardless of cross-head speed adopted. On the other hand, cyclic loading might have affected the CC tape in both upper anvil sizes adopted.
Gorospe, Alking B.,Shin, Hyung-Seop The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.4
REBCO coated conductor (CC) tapes with superior mechanical and electromechanical properties are preferable in applications such as superconducting coils and magnets. The CC tapes should withstand factors that can affect their performance during fabrication and operation of its applications. In coil applications, CC tapes experience different mechanical constraints such as tensile or compressive stresses. Recently, the critical current ($I_c$) degradation of CC tapes used in coil applications due to delamination were already reported. Thermal cycling, coefficient of thermal expansion mismatch among constituent layers, screening current, etc. can induce excessive transverse tensile stresses that might lead to the degradation of $I_c$ in the CC tapes. Also, CC tapes might be subjected to very high magnetic fields that induce strong Lorentz force which possibly affects its performance in coil applications. Hence, investigation on the delamination mechanism of the CC tapes is very important in coiling, cooling, operation and design of prospect applications. In this study, the electromechanical properties of REBCO CC tapes fabricated by reactive co-evaporation by deposition and reaction (RCE-DR) under transversely applied loading were investigated. Delamination strength of the CC tape was determined using the anvil test. The $I_c$ degraded earlier under transverse tensile stress as compared to that under compressive one.
Influence of Edge Geometry on the Delamination Strength of REBCO CC Tapes Using Anvil Test Method
Gorospe, Alking,Dedicatoria, Marlon James,Hyung-Seop Shin Institute of Electrical and Electronics Engineers 2016 IEEE transactions on applied superconductivity Vol.26 No.4
<P>In wet-wound epoxy impregnated coils, the whole coated conductor (CC) tape structure experiences radial/ transverse tensile stress due to large Lorentz force, which might induce delamination damage and in turn affects its transport performance during operation. The characterization of the delamination strength of CC tapes is therefore necessary for such practical applications. The anvil testing method was done to characterize the mechanical properties of REBCO CC tapes considering the possible transverse tensile stress condition in CC tape windings in coil applications. The delamination strength of three different CC tape samples slit from a 12-mm-wide one was determined using two different sized upper Cu anvils. It was observed that the slitting process has resulted to different CC tape edge geometries such as burrs and filleted corners of the substrate layer. As a result, significantly lower mechanical delamination strength was exhibited by the CC tapes when their whole width was covered by the upper anvil. Using the wide upper anvil, the edge geometry such as burrs and thick stabilizing layer played an important role on the delamination damage of the CC tape. Using a statistical method, the intrinsic strength of the CC tapes was distinguished from those that were affected by poor soldering, misalignment, and other external factors during the tests. Delamination sites mainly occurred within the REBCO film and on the buffer/REBCO interface. Finally, delamination schematics were drawn based on the delaminated CC tape's morphology.</P>
Gorospe, Alking,Bautista, Zhierwinjay,Hyung-Seop Shin,Oguro, Hidetoshi,Awaji, Satoshi IEEE 2017 IEEE transactions on applied superconductivity Vol.27 No.4
<P>Superior mechanical and electromechanical properties of the coated conductor (CC) tapes made them a viable option for coil and magnet applications. In this study, investigation on the characteristics of I<SUB>c</SUB> under different B, T, and ε conditions were conducted. Tensile load was applied using the Katagiri type test rig under different high magnetic field and low-temperature conditions wherein irreversible strain, ε<SUB>irr</SUB> was determined. The I<SUB>c</SUB> behavior with magnetic field of both reactive co-evaporation by deposition and reaction (RCE-DR) and metal organic chemical vapor deposition (MOCVD) processed CC tapes at different T and B were obtained. The critical irreversible strain limit ε<SUB>irr</SUB> of Cu-stabilized REBCO CC tape increased with decreasing temperature from 65 K down to 20 K. This behavior was resulted from the increased yield strength of the CC tape due to thermal hardening effect.</P>
Gorospe, Alking,Bautista, Zhierwinjay,Shin, Hyung-Seop IOP 2016 Superconductor science & technology Vol.29 No.10
<P>Coated conductor (CC) tapes utilized in high-current-density superconducting cables are commonly subjected to different loading modes, primarily torsion and tension especially in the case of twisted stacked-tape cable. Torsion load can occur due to twisting along the length or when winding the CC tapes around a former, while tension load can occur due to pre-tension when coiled and as a hoop stress when the coil is energized. In this study, electromechanical properties of single CC tapes under torsion load were investigated using a new test apparatus. The results could provide basic information for cable designers to fully characterize stacked cables. Copper-electroplated and brass-laminated CC tapes fabricated with different deposition techniques were subjected to pure torsion and combined tension-torsion loading. The critical current, <I>I</I> <SUB>c</SUB> degradation behaviours of CC tapes under torsional deformation were examined. Also, the effect of further external lamination on the <I>I</I> <SUB>c</SUB> degradation behaviour of the CC tapes under such loading conditions was investigated. In the case of the combined tension-torsion test, short samples were subjected to twist pitches of 200 mm and 100 mm. Critical parameters including reversible axial stress and strain in such twist pitch conditions were also investigated.</P>