We investigate the influence of lengthwise mechanical strain on the critical current (
Ic), the strain effects, for three kinds of “powder-in-tube (PIT)" route MgB
2 conductors. We tested
in situ monocore MgB
2/iron,
ex situ monocore MgB
2/stainless steel, and
ex situ 14-filament MgB
2/nickel tapes.
Ic was measured for each sample as a function of lengthwise external strain in magnetic fields (
B) at 4.2, 15, 20, and 25K using a U-shaped rig made of stainless steel. Even though the fabrication process and conductor configuration (number of filaments, width, and thickness) are different, the
Ic-strain relations were essentially the same in all MgB
2 samples. By increasing the strain, large and irreversible degradation occurred after linear and reversible
Ic-strain relation up to the maximum of
Ic (
Icm). The slope of linear
Ic-strain relation in the reversible regime, d(
Ic/
Icm)/d(strain), depends on both temperature and magnetic field. We discuss the relations between d(
Ic/
Icm)/d(strain) and magnetic fields normalized by the irreversibility field (
Birr.) We also examined the strain effect of
ex situ PIT monocore in Nb
3Sn/stainless steel tape. The
Ic-strain relation obtained is a parabolic one that has been reported so far for many kinds of multifilamentary Nb
3Sn conductors. This indicates that the linear strain dependence of
Ic in MgB
2 conductors is an essential feature of MgB
2.
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