Critical currents of MgB2 wires prepared in situ and ex situ subjected to axial stress

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Single-core MgB2 composite wires prepared by in situ and ex situ PIT processes weresubjected to axial tension and pressure. Their transport critical currentsIc were measured as afunction of axial strain ε with a U-shaped spring set-up at liquid helium temperature andexternal magnetic fields ranging from 3.5 to 6 T. For all wires,Ic changes linearly and reversibly with applied strain, up to a sample-dependent reversible strain limitεirr. Thevalue of εirr depends mainly on the degree of pre-compression, on themechanical properties of the sheath and also on the structure of theMgB2 core. In contrast to ex situ wires, the aspect ratio of in situ wires does not affect the value ofεirr. On theother hand, in situ wires are typically more sensitive to axial strain, i.e. they display a stronger reversibleIc variation and a steeper irreversible degradation, which is attributed mainly to the higherporosity of in situ cores.