Several researchers have shown that the material properties of hard coatings used in free layer damping treatments are dependent on the strain amplitude in the coating. This nonlinear phenomenon complicates the material characterization process and makes it difficult to find independent sets of data that are in complete agreement. During a recent in depth study of these materials, it became apparent that there were several other time and load history dependent nonlinearities present in these fascinating materials. These nonlinearities were observable because a free response based testing methodology was employed. Results indicate that the stiffness and damping of these materials change during the first several million loading cycles before finally stabilizing. Additionally, results suggest that the material properties are dependent on the initial condition of the free response, indicating a short term loading history dependency.

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