Relation of strength distribution of Nb3Al filaments to strength of multifilamentary superconducting composite wire

The distribution of tensile strength of Nb3Al filaments and its relation to tensile strength of Nb,AI multifilamentary superconducting composite wire were studied. The main results can be summarized as follows. (1) The tensile strength of the extracted filaments with an average diameter of 24 mu m was estimated based on the two-parameter Weibull distribution function. The shape and scale parameters were 7.0 and 530 MPa (for a standard length of 1 m), respectively. (2) Although the scatter of the strength of the Nb3Al filaments was large, that of the multifilamentary composite was very small. This means that, when a large number of filaments are embedded in a composite, the stress leading to overall fracture of the composite is not very different from sample to sample, even though the strengths of the embedded filaments are significantly different. This feature was confirmed by means of a computer-aided Monte Carlo simulation. (3) It was shown by experiment and simulation that the strength of the Nb3Al composite wire has a very slight dependence on length, although the strength of the Nb3Al filament decreases markedly with increasing length. This result indicates that, even if the length of the composite wire is extended from a short, laboratory scale sample to an industrial scale, the reduction in strength will be very small.