低温における鋼材内の超音波減衰

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Ultrasonic attenuation in solid is very sensitive to conditions under which the material is placed. Therefore the attenuation may be considered as a measuring factor of the properties of solid under the given condition. In the present paper, the result of measurement of the ultrasonic attenuation in normalized steel of 0・15, 0・4 and 0・55℃ at low temperatures down to -180℃ is reported and some conclusions are derived as to possible relation of the properties with the attenuation. The result shows that the attenuation decreases with the lowering of temperature and at around -60℃ to -80℃, the attenuation drops discontinuously by an appreciable amount, corresponding to the drop of Charpy's impact value of similar steels. Extension of Maxwell-type model to continuous body leads to the wave equation [numerical formula] where c is the coefficient of internal friction. The solution of this equation with the boundary conditions [numerical formula] [numerical formula] is given in the form of [numerical formula] where, A_0=A√<a^2+c^2ω^2> and as the first approximation, α is proportional to w^2 and c. The quadratic change of α with w agrees with the result of experiment within a certain of frequency but, with specimens of lower carbon content, additional attenuation appears to superpose, resulting a maximum attenuation at a frequency. Since α decreases with the temperature fall, the coefficient of viscous friction c in steels decreases with the lowering of temperature, contrary to the viscous friction of fluid which generally increases with the temperature fall. This seems to indicate that the drop of absorbed energy of a shock at low temperatures cannot be explained by the decrease of internal viscous friction of Maxwell model.
社団法人日本材料学会の論文
1957-08-15

低温における鋼材内の超音波減衰

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