Measurement of non-linear damping in metal-matrix composites

A method which does not require an accurate knowledge of the frequency, initial phase and initial amplitude of a free decay vibration is developed for the measurement of non-linear damping. Strain levels as low as one micro-strains are investigated. A multi-parameter Simplex inversion scheme is used to determine damping through a comparison of the theoretical and the experimental displacement. Using this method, we shall demonstrate that it is possible to measure the non-linear damping properties of materials from a single decay curve. By way of calibration, aluminum samples are used and the results show a significantly better precision in measurement than the log-decrement technique. Results are presented for Plexiglas, Mg-0.6%Zr alloy and the P55Gr/Mg-0.6%Zr composite.