Layered Sheet-Steel Damping Estimation Using Optical Vibrometry

Abstract

A non-contact modal analysis method is implemented to estimate the structural damping ratios for four stacks of sheet-steel, each bound using a different method. The setup comprised the four subject stacks and, for comparison, two single homogeneous steel plates of the same length and width with thicknesses that approximated the layered stack heights. To carry out the modal analyses, each test item was hung to simulate a free-free boundary condition. A force and frequency adjustable impact hammer imparted transient vibration to each hanging test piece after which the local relative velocity for each one of an array of discrete target points across the entire length-to-width surface was measured using an optical transducer. Damping ratios were extracted from the frequency response curves using the half power bandwidth method. Comparing the results obtained for the layered sheet-steel stacks with those from the homogeneous steel plates showed that damping ratios and loss factors can be estimated using the proposed experimental technique. The consistent impacts and the elimination of test structure mass loading improves the accuracy of damping estimates. In comparison to the solid plates, the layered sheet-steel stacks were characterized by increased damping. The effect was most significant for the stack bound together by polymer rivets.