EVALUATION OF INTERNAL LOSS FACTOR OF PLATES UNDER HARMONIC AND NON-HARMONIC EXCITATION

Abstract

The extensive use of plates, of different shapes & sizes and under varied loading conditions, in many fields of engineering applications necessitates an in-depth study of their static and dynamic behaviour. Whenever a plate is subjected to a dynamic load, vibrations are set up and it is possible that due to resonance the amplitude of vibration becomes very large. To control the amplified vibrations of the plate at resonance conditions various external arrangements may be made but the plate material in itself has an in-built mechanism to dissipate the input energy and it is termed as material-damping. The author has tried to highlight the importance of material damping in analysing the dynamic response of plates. In this dissertation, analytical formulation for evaluating the internal loss factor of simply supported "thin rectangular plate of constant thickness under harmonic and non-harmonic excitation has been done. Special emphasis is given to the importance of material damping under resonant conditions. The loss factor, based on dilatational strain energy criterion and distortional strain energy criterion, has been determined at different frequencies of periodic (square wave-like) excitation for 1. Central point load 2. Eccentric point load 3. Uniformly distributed load And the variation of r with excitation frequency has been plotted for the various cases considered. Also, the effect of change in load value and the, thickness of the plate on the iv internal loss factor has been studied. The modal ' loss factors for first five modes: of plate vibration under harmonic central point load & uniformly distributed load have been evaluated and compared with the values corresponding to non-harmonic excitation. In Chapter IV, simplified expressions and non-dimensional charts relating different cases have been obtained for harmonic uniformly distributed load