RELATION OF STRENGTH DISTRIBUTION OF NB3AL FILAMENTS TO STRENGTH OF MULTIFILAMENTARY SUPERCONDUCTING COMPOSITE WIRE

The distribution of tensile strength of Nb3Al filaments and its relati on to tensile strength of Nb,AI multifilamentary superconducting compo site wire were studied. The main results can be summarized as follows. (1) The tensile strength of the extracted filaments with an average d iameter of 24 mu m was estimated based on the two-parameter Weibull di stribution function. The shape and scale parameters were 7.0 and 530 M Pa (for a standard length of 1 m), respectively. (2) Although the scat ter of the strength of the Nb3Al filaments was large, that of the mult ifilamentary composite was very small. This means that, when a large n umber 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 signi ficantly different. This feature was confirmed by means of a computer- aided Monte Carlo simulation. (3) It was shown by experiment and simul ation that the strength of the Nb3Al composite wire has a very slight dependence on length, although the strength of the Nb3Al filament decr eases markedly with increasing length. This result indicates that, eve n if the length of the composite wire is extended from a short, labora tory scale sample to an industrial scale, the reduction in strength wi ll be very small.