引張り変形時における超電導Nb-50at%Ti線からのアコーステック・エミッション

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It is considered that sources of acoustic emission from superconducting magnets are mainly attributed to mechanical stress,wire motion and magnetic flux motion.In superconducting magnets, as the matter of fact, compound phenemena caused by these sources can be observed. One of the recent point of discussions about acoustic emission in the superconducting magnet is what the major source of acoustic emission is.It is necessary to investigate the mechanism of acoustic emission activities for diagnosing the state of the superconducting magnet. The acoustic emission activities of Nb-50at% Ti wires were measured during the tensile deformation at room temperatures, liq N_2 and liq He tempertures,respectively. Event count rate of acoustic emission were recorded by applying a stress with a constant rate of increase.The typical Kaiser effect were observed and many steps which seemed to be induced by micro slip in the sample were also measured in stress-strain curves at room temperatures and 77K.But,there was few acoustic emission corresponding to those steps,except for rather large steps( △σ⋍23.5MPa.△ε⋍-0.1%)which occured near the breaking point. In the superconducting state, on the other hand, typical burst type acoustic emission were found together with fine steps in the stress-strain curve.It was remarkable that event count rate gradually increased with increasing the tesile stress in bare samples. In copper-clad samples,however,event count rate increased in a lower stress region. This suggests that the acoustic emission in the superconducting wire is mostly due to a specific transformation such as the martensitic transformation,but plastic deformations of the copper must also heve some influences on the acoustic emission.
近畿大学の論文
1982-12-01

引張り変形時における超電導Nb-50at%Ti線からのアコーステック・エミッション

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