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The dynamic behavior of elastomers is usually characterized by linear viscoelastic models consisting of various combinations of linear springs and linear, viscous damping elements. The most commonly used model consists of a linear spring and a linear dashpot in parallel. The stiffness of the spring and the damping coefficient describe the dynamic behavior of the model. These properties are determined for a material under dynamic test conditions. Because the material is inherently nonlinear, it is not completely described by this model which compounds the testing problems. Furthermore, it is difficult to measure dynamic properties accurately. Any compliance in the test machine will usually affect the measured spring rate, and damping in the test machine will usually add to the measured damping coefficient. A recent analytical study of the resonant-beam test machine has quantified these effects. These results have prompted the move toward transmitted force methods for testing in which the force transmitted through the sample and motion across the sample are the measured signals. From these signals the dynamic properties are then computed; however this places very strict requirements on the instrumentation and computation system. The principles of measurement systems applicable to dynamic testing are presented. Test equipment along with recent developments in instrumentation and test methods are described. The test conditions which influence the results are also reviewed. The present state of the art of forced vibration dynamic testing of elastomers is presented.
elastomers, viscoelasticity, dynamic properties, test equipment, damping, viscosity
Alcoa Professor of Engineering, School of Mechanical Engineering, Purdue University, West Lafayette, Ind.