A novel technique to extract the modal damping properties of a thin blade

Abstract

Extracting accurate material modal damping from a specimen can be very challenging due to the potential influence of the excitation and measurement system, and the required support of the specimen. This becomes particularly challenging if large amplitudes are required to determine nonlinear behavior, or large damping is present due to the material under investigation. An improved approach is proposed here to enable large amplitude, single harmonic, free decay damping extraction of a flat test specimen. It is based on a setup that uses the inertia of two large, free hanging end masses to enforce a pinned-pinned boundary condition with predetermined nodal locations, ensuring minimum effect of the support structure on the damping behavior. Excitation is achieved with the help of a removable electromagnetic shaker system that enables large amplitude single harmonic excitation, and smooth transition to a free, single harmonic decay. A Laser Doppler Vibrometer is used to measure the free decay, from which amplitude dependent damping can be obtained for individual modes via logarithmic decrement. Initial results of the approach show its great potential to provide reliable, amplitude dependent parameters with minimum impact of the test setup.