Recent advances in the use of the impulse excitation technique for the characterisation of stiffness and damping of ceramics, ceramic coatings and ceramic laminates at elevated temperature

In this paper, recent advances in the impulse excitation technique (IET) are presented. IET is based on the frequency analysis of the resonant vibration of a gently struck test sample. IET has become a widely accepted standard method for the determination of accurate stiffness and damping values for monolithic materials. The non-destructive, non-contacting character of the technique has made it possible to implement IET in high temperature furnaces. Results are shown from tests on SiC samples up to 1450 degreesC. In addition, two new developments are reported. First, the measurement of the stiffness of small disk-shaped samples is discussed. A solution for the suspension of small disk samples in furnaces will be demonstrated. Further, the use of the technique for the investigation of layered materials will be discussed. The elastic properties of a symmetrically applied coating (coating/substrate/coating) can be deduced from the flexure resonance frequency of the composite body, given the properties of the substrate. Similar analytic solutions exist for multilayer systems composed of two materials, involving the flexure as well as the longitudinal resonance frequencies. An example will be shown of a Al2O3-Y-TZP/Y-TZP laminate consisting of 9 layers.