CRITICAL ASSESSMENT OF THE ISSUES IN THE APPLICATION OF HILBERT TRANSFORM TO COMPUTE THE LOGARITHMIC DECREMENT

摘要

The parametric OMI (Optimization in Multiple Intervals), the Yoshida-Magalas (YM) and a novel Hilbert-twin (H-twin) methods are advocated for computing the logarithmic decrement in the field of internal friction and mechanical spectroscopy of solids. It is shown that dispersion in experimental points results mainly from the selection of the computing methods, the number of oscillations, and noise. It is demonstrated that conventional Hilbert transform method suffers from high dispersion in internal friction values. It is unequivocally demonstrated that the Hilbert-twin method, which yields a 'true envelope' for exponentially damped harmonic oscillations is superior to conventional Hilbert transform method. The 'true envelope' of free decaying strain signals calculated from the Hilbert-twin method yields excellent estimation of the logarithmic decrement in metals, alloys, and solids.