The amplitude of vibration in a structure undergoing resonant vibration is governed by the total damping of the system. As the inherent damping of materials suitable for use in the fabrication of structures and machine components is often quite low, increasing the total system damping by including a dissipative material or mechanism can often provide significant reductions in the peak values of response (stress, strain, and displacement), enabling more efficient designs and enhanced performance. Available methodologies include active dampers and such passive techniques as friction and impact dampers and constrained layer treatments. It has also been found that metals and ceramics applied as free-layer hard coatings by plasma spray or electron beam physical vapor deposition add significant damping to vibrating members. In order to incorporate the influence of a damping coating in a prediction of system response during a preliminary design, it is essential that properties of the coating be known. The relevant damping characteristic is a measure of the energy dissipated by a homogeneous unit volume of material undergoing a completely reversed cycle of oscillation. A useful metric for this is the loss modulus. As all of these materials are inherently non-linear, as evidenced by amplitude-dependent measures of damping, determinations of properties must be made at the levels of strain appropriate to the application. Methods for determining the damping properties of materials are discussed, and comparisons are made of the damping of various classes of materials with those of ceramic coatings deposited by plasma spray or electron beam physical vapor deposition.
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