Nb_3Sn超导股线热应变分析模型研究

Thermal Strain Analysis Model of Nb_3Sn Superconducting Strands

ITER聚变反应堆上Nb3Sn超导股线是由脆性金属间化合物构成的,由于其间各组分不同的热胀冷缩系数和不同的弹性模量,使得股线从热反应温度或热处理温度到室温、以至到低温运行时,会在Nb3Sn复合物中产生热应变。为了研究Nb3Sn的热应变和构建相应的数学模型,进行了加热期间局部应变测量以及室温下的拉力测试。根据Nb3Sn股线不同组分应力/应变曲线所显示的弹塑特性,对它们进行量化分析。测试分析发现,在室温下沿轴向加载到Nb3Sn超导丝的局部应变是压缩应变,高温下是拉应变;另外用数值分析计算方法可以再现依靠温度的轴向热应变。

The Nb3Sn superconducting strands used for ITER （international thermal-nuclear experimental reactor） consist of brittle intermetallic compounds. Due to the different coefficients of thermal expansion and different moduli of elasticity among the components, thermal strain is generated in the composite from heat treatment temperature down to room temperature, even to operating temperature （4.2 or 4.5 K）. In order to research thermal strain and build the mathematic model of the Nb3Sn strands, local strain measurements during heating by means of quantum beams and tensile tests at room temperature were carried out. According to the elasto-plastic behavior of Nb3Sn revealed in the stress curves, the thermal strain was evaluated. The results show that the local strain exerted on superconducting （SC） filaments along the axial direction is compressive at room temperature and tensile at high temperatures. Moreover, the temperature dependence of thermal strain can be reproduced well by the numerical calculation method proposed in the paper