Experimental Study on Fatigue Properties of REBCO Mechanical Lap Joint Under Cyclic Tensile Loading

High-temperature superconducting mechanical joint, which can be dismantled, plays a particularly important role in the fabrication of demountable magnet for fusion device. In this article, the mechanical lap joint using indium foil as bonding material is manufactured. First, the monotonous tensile character of the lap joint is studied, and then mechanical characteristics under tensile fatigue loading are tested in different conditions, such as applied pressure in the production process, stress ratio, holding time, and loading frequency of cyclic loading. The monotonous test shows that the critical current of lap joint gradually decreases as the tensile load increases at first stage, and then drastically reduces as the tension reaches a certain value. Meanwhile, after the critical current has already been permanent degradation, the joint resistance gradually increases as the tensile load increases. The tensile fatigue loading test shows that the lower the applied pressure in production process, the shorter cycle life of the joint. When the stress ratio is larger, the joint resistance increases more obviously with the increase of the loading cycles. Moreover, lower frequency or longer holding time under maximum tension makes the critical current degradation more obvious and the fatigue life of the joint shorter.