Experimental determination of damping ratios at higher modes for use in modal superposition

Abstract

While carrying out the transient analysis, the major challenge is to provide accurate damping ratio data for higher modes as this is not reported. Hence an attempt is made to find out the damping ratios experimentally in this paper. Two approaches of experimental evaluation of damping ratios are discussed, for free and forced vibration, with four different materials namely: mild steel, aluminum, cast iron and plastics. For the first set, eleven cantilevers of uniform cross section with varying lengths are taken for evaluation. For the second set, fourteen components made of these materials used in air brake system of automobiles are also examined. For the free vibration, impact test is used to find the fundamental natural frequency and damping ratio. In forced vibration study, electro dynamic shaker is used to find the first three natural frequencies and damping ratios. Besides the above methods, natural frequencies are calculated analytically using finite element analysis (FEA). Based on the exhaustive experimental work carried out design guidelines on damping ratios for industrial problems are presented.