Transient Vibration Experiments for Determination of Properties for Viscoelastic Structures

Abstract

Two experimental techniques devised to determine the mechanical properties for viscoelastic structures are demonstrated with experiments on polymethyl methacrylate (PMMA). Circular rings are loaded with an axisymmetric impulse which excites the fundamental membrane mode and free-free beams are loaded with a spatially distributed impulse which excites the fundamental bending mode. Because only one mode of vibration is excited, these structures can be regarded as single-degree-of-freedom systems in free vibration. Loading is produced by magnetic pressure pulses and the response is measured with strain gages. The complex modulus is obtained from period of vibration and logarithmic decrement of the strain response. Geometry of the specimens is varied to obtain complex moduli over a wide range of frequencies.