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The Optimum Use of Unconstrained Layer Damping Treatments

Report Number: ML TDR 64-51
Author(s): D. J. Mead and T. G. Pearce
Corporate Author: University of Southampton
Laboratory: Air Force Materials Laboratory
Date of Publication: 1964-08
Pages: 51
Contract: AF 61(052)-504
Project: 7351 - Metallic Materials
Task: 735106 - Behavior of Metals
AD Number: AD0607244

Since unconstrained layer damping treatments on vibrating plates dissipate energy by undergoing bending strain, the treatment in the vicinity of lines of contra-flexure contributes little to the total damping. This report investigates the effect of concentrating the treatment in the regions of highest bending moment in order to use all the material more effectively. Three methods of analysis are presented, two of them being approximate but relatively rapid in use. The third has been used in extensive digital computer calculations to determine the effectiveness of given quantities of treatment, having given stiffness, when distributed over different proportions of the length of a vibrating, simply supported strip. The effectiveness has been assessed using certain criteria which apply to different problems, e.g. to the problems of reducing harmonic resonant vibration amplitudes, or inertia forces exerted by randomly vibrating panels, etc. Different criteria relate to each problem. It has been shown that very considerable increases of effectiveness are obtained by concentrating the treatment over a proportion of the length or area. For a given quantity and stiffness of treatment, the effectiveness may be maximised by covering certain optimum proportions. The optimum proportions corresponding to different criteria differ only slightly, permitting curves to be drawn showing the 'mean' optimum coverage required for a wide range of given quantities of treatment, and for a range of treatment stiffness. An experiment is described which confirms the validity of the theoretical approaches. The effects of temperature changes on the criteria values are also briefly considered, and it is concluded that the temperature bandwidth of the treatment when partially covering the plate is not significantly different from that when uniformly covering the plate.

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