AN EXPERIMENTAL-METHOD FOR CONSIDERING DISPERSION AND ATTENUATION IN A VISCOELASTIC HOPKINSON BAR

An experimental method is developed to perform Hopkinson tests by mean s of viscoelastic bars by considering the wave propagation attenuation and dispersion due to the material rheological properties and the bar radial inertia (geometric effect). A propagation coefficient, represe ntative of the wave dispersion and attenuation, is evaluated experimen tally. Thus, the Pochhammer and Chree frequency equation is not necess ary. Any bar cross-section shapes can be employed, and the knowledge o f the bar mechanical properties is useless. The propagation coefficien ts for two PMMA bars with different diameters and for an elastic alumi num alloy bar are evaluated. These coefficients are used to determine the normal forces at the free end of a bar and at the ends of two bars held in contact. As an application, the mechanical impedance of an ac celerometer is evaluated.