Determination of mechanical properties of non-linear coatings from measurements with coated beams

Coatings are applied to structural components for several various reasons, such to protect against erosion or corrosion, as thermal barrier coatings, or to increase the energy dissipation. As determining the material properties of such coatings from homogeneous specimens is often difficult, it is sometimes necessary to conduct testing on coated specimens, with the properties of the coating then to be extracted from the results of testing. A methodology for doing this is given here. While applicable to other materials, the properties of such coatings as ceramics, metallics, or compounds to be applied to rotating and static components of gas turbines are of special interest. Such materials present a special challenge as the mechanical properties have generally been found to display a strong dependence on the amplitude of cyclic strain. Application of the methodology requires careful measurement of specimen dimensions, weights, natural frequencies, and system loss factors before and after coating. From these, the storage (Young’s) modulus, the loss modulus, and the loss factor can be extracted. The methodology is demonstrated through the use of data taken on flat specimens of titanium with plasma-sprayed coatings of NiCrAlY and a titania–alumina blend ceramic, vibrating in a cantilever mode.