Damping Performance Measurement of Non-uniform Damping Treatments

In industrial applications, both constrained and unconstrained damping treatments are used frequently for noise and vibration control. The additional Damping Loss Factor (DLF) and stiffness gained from these damping treatments are quantified by a standard test procedure, as detailed in ASTM and SAE standards. In this test procedure, which is commonly referred to as Oberst beam testing, the uniform isotropic behavior of traditional damping material is evaluated by measuring one-dimensional flexural vibration response of a simple beam. The recent advances in damping technology have led to emergence of robotic Liquid Applied Spray-on Damping (LASD) treatments. The application of LASD can result in non-uniform thickness, uneven distribution, and orthotropic behaviors. This lack of uniformity raises serious concerns in use of Oberst beam samples; first, the preparation and quality of samples becomes an issue, and then, the material properties extracted from these samples become questionable. In this study, a square panel is proposed as a proper medium for evaluation of non-uniform LASD treatments, where the DLF measured from two-dimensional flexural vibrations of the plate is the main interest. The need for a new approach for non-uniform damping treatments is established by presenting a theoretical argument and practical evidence. In this study, a special experimental test apparatus is proposed to acquire data using the new approach. The accuracy of this approach is validated by testing different constructions; later, a variety of LASD samples were measured using this new approach. The findings of the study highlight the limitations of the Oberst beam method for evaluation of non-isotropic materials. This study introduces a new way of testing non-uniform orthotropic damping treatments, and paves the way for a new standard.