Calculated stress distribution in a PbMo6S8 wire performing the Ic vs. ϵ experiment

The precompression of the superconducting filament in a PbMo₆ S₈ monofilamentary wire at 4.2 K. which was experimentally observed as a prestrain in an I_c vs. ε experiment, was simulated with the calculation of the thermal stress distribution using a triaxial elastic stress model. The occurrence of different prestress conditions, due to the choice of different barrier materials (Ta, Nb, and Mo) and as consequence of a varying reinforcing stainless steel content, was investigated by calculations and compared with experimental results. The change of the stress state in the filament with external axial stress shows a significant amount of hydrostatic stress even at the J_c maximum, which explains the observed degradation of superconductivity. For the presently used Chevrel-phase wire configurations with the unfavorable thermal expansion of the barrier materials, the hydrostatic stress component, e.g. the radial stress in the filament. is important for achieving a good bonding at the layer interfaces and creating the wanted prestress in the filament. If no alternative methods and materials for the barrier are found in the future, enhanced mechanical wire properties can only be obtained by a reduced layer thickness of the barrier, which would additionally improve the overall critical current density of the wire