EXPERIMENTAL AND ANALYTICAL DETERMINATIONS OF MECHANICAL IMPEDANCE RESPONSE OF ANIMALS TO VERTICAL VIBRATION

Although high acceleration intensities are at times encountered in vehicles and machinery, man cannot, for safety reasons, serve as a laboratory subject in high intensity vibration tests. In such cases, animals have typically been used as human surrogates. The mechanical impedance of sitting, unanesthetized rhesus monkeys and dogs is determined for vertical, sinusoidal vibration. The animals were briefly (30 sec) exposed at discrete frequencies from 2 to 30 Hz at acceleration amplitudes of 0. 5 and 1. 0 g. The experimental data were applied to a two-mass, single-degree-of-freedom model to determine the whole body coefficients of elasticity and damping as a function of frequency and body mass. The coefficients were obtained for each test at each frequency by requiring the impedance of the model to match that measured from the animals. A part of the model is an empirical equation defining the ratio of non-reactive to reactive animal mass as a function of vibration frequency and intensity. The impedance response of the model for the monkey and also that for the dog closely matched experimental results throughout the 2 - 30 Hz range at 0. 5 and also at 1. 0 g.