Tuesday, 12 October 2004 - 1:25 PM

This presentation is part of : Wineman Symposium

Broadband viscoelastic spectroscopy of alloys and composites over eleven decades of time and frequency

T Jaglinski, R. S. Lakes, and P Frascone, graduate student. University of Wisconsin, Engineering Mechanics, Madison, WI 53706

Mechanical damping, tan delta (δ), of various materials intended for vibration damping applications was determined experimentally over a wide range of frequency and time, up to eleven decades (a factor of one hundred billion) from slow quasistatic tests to 100 kHz in the ultrasonic domain, using a unique broadband viscoelastic spectroscopy (BVS) apparatus. No appeal is made to time temperature superposition; all experiments were done at the same temperature. Broadband capability of the BVS instrument is particularly useful in the study of materials which are not thermorheologically simple. The wide frequency range is obtained by eliminating resonances from the devices used for loading and for displacement measurement, by minimizing the inertia attached to the specimen, and by use of a geometry giving rise to a simple specimen resonance structure amenable to simple analysis. Torque was produced by the electromagnetic action of a Helmholtz coil upon a high intensity neodymium iron boron magnet at the specimen free end. The electrical input was sinusoidal for dynamic studies and step function for creep studies. In the subresonant domain, tan δ was inferred from the phase angle between torque and angle. Various alloys (including InTl and ZnAl) in the vicinity of phase transformations as well as their composites were fabricated and studied. Constrained materials undergoing phase transformation can be associated with negative stiffness.

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