Development of high-resolution mechanical spectroscopy, HRMS: Status and perspectives. HRMS coupled with a laser dilatometer

Abstract

Recent achievements in the development of low-frequency high-resolution mechanical spectroscopy (HRMS) are briefly reported. It is demonstrated that extremely low values of the loss angle, φ, ( tanφ b= 1×10-5) can be measured as a function of frequency, and the precision in estimation of the dynamic modulus is better than 1×10-5 in arbitrary units. Three conditions must be fulfilled to obtain high resolution in subresonant and resonant mechanical loss measurements: (1) noise in stress and elastic strain signals must be lower than 70 dB, (2) high quality of stress and strain signals must be tested both in the frequency- and time-domains, and (3) the estimation of the mechanical loss and modulus must be verified by at least two different computing methods operating in the frequency- and time-domains. It is concluded that phase measurements in the subresonant domain are no longer determined by precision in estimation of the loss angle. Recent developments in high-resolution resonant mechanical loss measurements stem from the application of advanced nonparametric and parametric computing methods and algorithms to estimate the logarithmic decrement and the elastic modulus from exponentially damped free decaying oscillations embedded in experimental noise. It is emphasized that HRMS takes into account the presence of noise in the stress and strain signals, which has not yet been addressed in the literature. The coupling of a low-frequency mechanical spectrometer with an in-situ laser dilatometer is suggested as a new perspective research area in Materials Science.