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A complete set of critical current data for a Nb3Sn bronze wire under axial and transverse loads has been measured as a function of magnetic field in the range between 12 and 19 T. For this purpose a new probe was developed for the application of a transverse compressive force with a gauge length of 120 mm. The device is based on a one-turn Walters spring, thus circumventing the problem of current transfer. The probe allows the application of voltage criteria of 0.01 µV cm−1 or less, allowing a detailed study of the n values. As expected, the conductor is more affected by transverse compressive stress than by axial tensile stress. The conductor already starts to degrade at small transverse stresses and the rate of degradation increases with the magnetic field. On the wires measured so far, unloading from 160 MPa yields a recovery of the critical current to 87% of its initial value. The obtained results encourage further investigations of differently processed Nb3Sn superconductors (internal tin, powder in tube) or others (e.g. Nb3Al) and may be helpful for modelling.

High-performance Nb3Sn conductors are intended to be used in large-scale magnets like the International Thermonuclear Experimental Reactor (ITER) and in the upgrade of the Large Hadron Collider (LHC). Due to the occurrence of high electromagnetic forces, a detailed knowledge of the response of the critical current to the three-dimensional mechanical loads acting on the wires inside the cables is required. A detailed analysis of transverse stress effects on the critical current for powder-in-tube and bronze route Nb3Sn wires is presented. In an earlier publication, we have described the effect of transverse stress exerted on a Nb3Sn wire by means of two parallel plates. In the present paper, we analyse the effect of transverse stress exerted simultaneously by four walls on a wire being confined in a U-shaped groove. In order to get a more realistic picture of the situation of wires embedded in a Rutherford cable, the compression by four walls was also performed after impregnating the wire with epoxy in the same U-shaped groove. The result is very different from the case of pressing by means of two walls: the effect of pressure on Ic is now strongly reduced, which is attributed to the almost hydrostatic pressure in the U-shaped groove. This is further confirmed by the comparison between the effects of axial and transverse loads on the upper critical field and the pinning force. The present data are also compared against the effects of mechanical load on the critical current of cables in large-scale magnets.

Polymer/carbon nanotube (CNT) composite monofilaments were produced and tested for sensing activity. Polylactide (PLA) was the polymer selected for humidity sensing, while a mixture of polypropylene (PP) and poly(ε-caprolactone) (PCL) was used for temperature sensing. The PP/PCL/CNT composite filaments developed a co-continuous structure with CNT localized in the PCL phase. The filaments were characterized in terms of tensile properties and electrical resistivity. Textile fabrics were produced with both types of filaments. The electrical resistance of the fabrics subjected to humidity or temperature variations was measured in a climatic chamber.

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The electromechanical behavior of a Nb 3 Al wire manufactured according to the RHQT process (rapid-heating, quenching and transformation) has been investigated at magnetic fields between 15 and 19 T at 4.2 K. Of particular interest was the critical current, I c , as a function of transverse pressure up to 300 MPa and as a function of axial tensile stress. The studied wires are pieces of a 870 m long copper stabilized Nb 3 Al wire with a rectangular cross section of 1.81 mm × 0.80 mm. It was observed that the critical current at 300 MPa transverse pressure, applied to the narrow side, is reduced to 93%, 90% and 88% of its stress free value at 15 T, 17 T and 19 T, respectively. After unloading from 300 MPa I c recovers to 94% and 97% at 19 T and 15 T, respectively. A field dependence of the effect is visible above 200 MPa. For completeness, the critical current was also measured under axial tensile strain. The maximum of I c is at 0.15% applied strain and irreversibility has been observed above 0.26%. Finally a stress versus strain measurement at 4.2 K has been carried out allowing the conversion from axial strain to stress.

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