APPARATUS FOR MEASURING VISCOELASTIC PROPERTIES OVER 10 DECADES - REFINEMENTS

This paper describes refinements to an instrument for determining the viscoelastic properties of a solid material isothermally, with a single apparatus, over 10 decades of time and frequency. Torque is applied electromagnetically to a specimen fixed at one end. Specimen deformation is determined via a laser beam reflected from the other end upon a split diode detector. Phase resolution is improved by the use of a lock-in amplifier at high frequency and by the use of Lissajous figures to measure phase, allowing the study of materials of moderate loss (0.008 less than or equal to tan delta less than or equal to 0.2) in addition to materials with high loss (tan delta approximate to 1). The rigidity of the instrument is increased by modifications in the specimen support geometry. The range of equivalent frequency for torsion is from less than 10(-6) Hz to more than 10(4) Hz. Digital methods are incorporated in the creep measurements and in the phase measurements. (C) 1995 American Institute of Physics.