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Description
In previous studies, Jc-strain relation in the reversible range and the irreversible external-tensile strain (ε_irr_t) of MgB2 filament were reported. In general, it is said that ε_irr_t is almost equal to the pre-compressive strain caused by cooling after heat treatment. In this study, the irreversible external-compressive strain (ε_irr_c) of MgB2 multifilament wire was measured. In measurements, a copper plate was soldered to a sample wire, then the sample wire was bent while the copper plate was applied outward. ε_irr_c can be measured by evaluating Ic vs bending-radius relation, because the external tensile strain by bending is negligible in this situation. In the damaged sample wire, some buckling were observed in inner filaments on bending. It suggests that the irreversible damage was made by compressive strain. In addition, ε_irr_c of additional sample wires, which have larger pre-compressive strain and were heat treated by higher temperature were measured. The difference values between ε_irr_t and ε_irr_c of samples were roughly same value. From this results, we can minimize the reversible bending radius by controling pre-compressive strain and thickness of copper plate.
