42 wt%Mn-2 wt%Al-Cu合金板の減衰能の異方性

Abstract

The measured anisotropy of damping capacity has been compared with the one calculated using a model of static hysteresis damping. The results show that not simple but rather complex mechanisms are responsible for the damping capacity of this alloy.Test pieces 1.7 mm in width and 110 mm in length were cut from a 80% cold-rolled sheet 0.5 mm in thickness with the angle α to the rolling direction, and quenched from 750°C. Their specific damping capacity (SDC) has been measured at −30∼+30°C by a torsional pendulum method (∼0.25 Hz) in the course of ageing at 400°C.In the range of applied shear strains 3×10−5∼12×10−5, SDC increases approximately linearly with increasing strain amplitude. The strain independent SDC, which was obtained by a linear extrapolation of SDC to strain amplitude ε=0, is independent of the angle α, while the strain dependent SDC, which was deduced from the whole SDC by subtracting the strain independent one, shows some dependence on the angle α.The dependence of the damping capacity on the angle α has been calculated on the assumption that SDC is proportional to the volume swept by twin boundaries in compliance with the strain induced re-orientation of their tetragonal lattice distortion. Preferred orientations in the sheet necessary for this calculation are estimated from the pole figure data and the observed anisotropy of rigidity modulus. The observed anisotropy of the strain dependent SDC has been revealed to be affected by the ageing condition and to be always smaller than the calculated one.The damping capacity of this alloy should be therefore interpreted as consisting of three components, i.e. the component independent of both strain and crystal orientation, the component dependent on strain but not on crystal orientation, and the component dependent on the two.The contribution of each of these three components is expressed as a function of ageing time and damping measurement temperature, and the corresponding mechanism is discussed.