Thermo-mechanical properties of bulk high Tc, superconductors

1循环热冲击：对大型单磁区Dy123块材进行了110次循环热冲击拉伸试验。虽然弹性模数E和极限抗拉强度UTS在a、b轴上没有变化，但在c轴上下降了一半。在较小的试件中，UTS和断裂韧性均未发现损伤。热循环使附着在钛棒上的试件的抗弯强度略有降低。在添加Dy123块体的10wt%Ag颗粒中，E值略有下降，而UTS有所增加。颗粒通过颗粒附近的残余压缩应力来防止热损伤，有限元分析软件Ansys对快速冷却后的非稳态热应力进行了分析，解释了上述不同尺寸试件损伤的差异。结果表明，随着块体直径增加到100 mm，块体厚度增加，热应力增大，但在厚度为25 mm时达到饱和。纯样品a、b轴的最大热应力较大，含银样品的c轴最大热应力较大。这是由于c轴具有较高的热导率和E。2块体-金属复合材料：直接粘结或通过块体中间层粘结到Al和Ti棒上的块体样品在77K的UT按顺序较高。虽然粘着铝的试件在高热应力区断裂，但在有夹层的试件上则不是这样。UTS与有限元模拟拉伸试验中的最大应力相对应。3低温热力参数：利用我们的传导冷却制冷式系统，评估了20K以下块体和金属的导热系数和热膨胀系数与热应力的温度关系。

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.