Abstract
A pendulum-type viscoelastic spectroscopy is developed to experimentally measure loss tangent and the magnitude of dynamic modulus of solid materials. The experimental apparatus consists of the Helmholtz coils to generate torsion and pure bending moments on the cantilever beam specimen. A permanent magnet is attached to the free end of the specimen to interact with the magnetic field generated by the Helmholtz coil. Sinusoidal driving signals are adopted for measuring complex modulus, and dc bias driving for creep tests. Deformation is monitored by the laser-based displacement measurement system. In the sub-resonant frequency regime, the complex modulus can be obtained by directly analyzing Lissajous stress-strain curves, provided the phase angle is not extremely small. At the structural resonant frequency, the Lissajous method fails, and hence the full-width-at-half-maximum (FWHM) method or lorentzian curve fitting method is adopted. In the low frequency limit, the loss tangent can be calculated from measured creep compliance with the Kramer-Kronig relationship.
