Differences and similarities in fatigue behaviour and its influences on critical current and residual strength between Ti-Nb and Nb3Al superconducting composite wires
Differences and similarities in fatigue behaviour and its influences on critical current and residual strength between Ti-Nb and Nb3Al superconducting composite wires
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Ti-Nb与Nb3Al超导复合线材疲劳行为的异同及其对临界电流和残余强度的影响
DOI：
10.1088/0953-2048/13/4/311
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发表时间：
2000
影响因子：
3.6
通讯作者：
Kazuo Watanabe
中科院分区：
文献类型：
--
作者：
Shojiro Ochiai;Y. Oki;Fumiaki Sekino;H. Ohno;M. Hojo;H. Moriai;S. Sakai;M. Koganeya;K. Hayashi;Y. Yamada;N. Ayai;Kazuo Watanabe
研究了室温疲劳损伤对低铜比(1.04)Ti-Nb超导复合丝4.2K的临界电流和室温剩余强度的影响。并与Nb3Al复合材料的实验结果进行了比较。结果表明，TiNb复合材料的断裂表面由静载荷下的延性断裂转变为循环载荷下的脆性断裂，而Nb3Al复合材料在两种载荷下均表现为脆性断裂；TiNb复合材料的断裂强度由净应力准则给出，而Nb3Al的断裂强度由应力强度因子准则给出；在TiNb复合材料中，临界电流Ic随应力循环次数的增加而减小，同时随残余强度c，r的增加而减小，而在Nb3Al复合材料中，Ic降低的时间晚于c，r。另一方面，两种复合材料都有如下相似之处：疲劳裂纹在铜中的形核导致纤维断裂；随着应力循环次数的增加，损伤按阶段I(覆铜中裂纹的形成)、阶段II(疲劳裂纹向内芯的稳定扩展)和阶段III(整体断裂)的顺序发展，其中阶段II发生在超过85%~90%的疲劳寿命的后期；在中等最大应力下，许多大的裂纹在不同的截面上扩展到芯部，但在高和低最大应力下没有；相应地，对于中等最大应力，远离主裂纹的部分的临界电流和剩余强度较低，而对于低最大应力和高最大应力则不是。
The influences of fatigue damage introduced at room temperature on critical current at 4.2 K and residual strength at room temperature of Ti-Nb superconducting composite wire with a low copper ratio (1.04) were studied. The experimental results were compared with those of Nb3 Al composite. The following differences between the composites were found: the fracture surface of the Ti-Nb filaments in the composite varies from a ductile pattern under static loading to a brittle one under cyclic loading, while the Nb3 Al compound always shows a brittle pattern under both loadings; the fracture strength of the Ti-Nb composite is given by the net stress criterion but that of Nb3 Al by the stress intensity factor criterion; in the Ti-Nb composite the critical current Ic decreases with increasing number of stress cycles simultaneously with the residual strength c ,r , while in the Nb3 Al composite Ic decreases later than c ,r . On the other hand, both composites have the following similarities: the filaments are fractured due to the propagation of the fatigue crack nucleated in the copper; with increasing number of stress cycles, the damage progresses in the order of stage I (formation of cracks in the clad copper), stage II (stable propagation of the fatigue crack into the inner core) and stage III (overall fracture), among which stage II occurs in the late stage beyond 85 to 90% of the fatigue life; at intermediate maximum stress, many large cracks grow into the core portion at different cross sections but not at high and low maximum stresses; accordingly, the critical current and residual strength of the portion apart from the main crack are low for the intermediate maximum stress but not for low and high maximum stresses.