Thermo-mechanical properties of bulk high Tc, superconductors

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1 Cyclic thermal shocks : Tensile tests on the specimens cut from large single domain Dy123 bulk subjected to 110 cycles of thermal shock by cooling to 77K have been conducted. Although the Young's modulus, E, and the ultimate tensile strength, UTS, did not change in a, b axis, they decreased to half in c-axis. In the small specimens, no damage was found in UTS and the fracture toughness. The thermal cycle slightly lowered the UTS of specimen adhered to Ti rod. In the 10wt% Ag particle added Dy123 bulk, E slightly decreased and UTS increased. The particles prevent the thermal damage through the compressive residual stress near the particle.The finite element method analysis, ANSYS, on the non-steady state thermal stress by rapid cooling explained the difference of damage in specimens with different size mentioned above. It was shown that the increase in diameter to 100 mm and thickness of the bulk raise the thermal stress but it saturates at 25 mm thickness. While the maximum thermal stress in a, b axis was larger in plain sample, those in c-axis was larger in Ag added sample. This is due to the higher thermal conductivity and E in c-axis.2 Bulk-metal composite : The UTS at 77K of the bulk specimens adhered directly or via the bulk interlayer to the Al and Ti rods were higher in the order. Although the specimens adhered to Al were broken in the high thermal stress region, it was not the case in specimens with interlayer. The UTS corresponded with the maximum stress in the FEM simulated tensile test.3 Cryogenic thermal parameters : Using our conduction cooling refrigerating type system, the temperature dependence of thermal conductivity and coefficient of thermal expansion relevant to the thermal stress of bulk and metals down to 20K were evaluated.