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

The low-strain (0.1 to 20%) amplitude behavior of elastomeric materials in simple shear was investigated both experimentally and analytically. Amplitudes, temperatures (-40° to 150 °F), 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 ADF 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. Additional single- and dual-frequency harmonic data (nonlinear stress time-histories) was then used to validate the current model. The model accurately represents the material behavior for these loading conditions. Experimental investigations were further expanded to examine the influence of temperature and static precompression.