Characterization and modeling of the low strain amplitude and frequency dependent behavior of elastomeric damper materials

The low strain amplitude behavior of elastomeric materials in simple shear was investigated both experimentally and analytically. Amplitudes (0.1 to 20%) and frequencies (0.01 to 10 Hz) were chosen to represent the working range of typical helicopter damper applications. A nonlinear model was developed to capture the combined amplitude and frequency dependence. The model extends the nonlinear Anelastic Displacement Fields (ADF) approach to include friction-type elements. These elements operate in parallel with the original ADF model. This configuration is shown to improve the performance of the model over the amplitude and frequency range of interest. Experimental tests (single frequency harmonic) were conducted at several frequencies and amplitudes to support model characterization. The current model and a baseline nonlinear model (which does not include friction-type elements) were characterized using linearized material complex modulus data. The current model captures observed material behavior more accurately than the baseline model. Specifically, the peak error between predicted and experimentally determined material complex moduli was reduced from 72% to 18% for the storage modulus, and from 90% to 10% for the loss modulus. Over the frequency and amplitude range of interest, the average error was reduced from 36% to 8% for the storage modulus, and from 33% to 4% for the loss modulus. Single and dual frequency harmonic and quasistatic data (nonlinear stress time histories) were used to validate the current model. These data were not used in the model characterization. The model accurately represents the material behavior for these loading conditions.