Loss Factor of Elastomeric Dampers for Rotating Machinery Application

Elastomeric dampers have potential application in rotating machinery vibration control. They are however not widely used due to lack of reliable data on their loss factor. Most available data on these dampers are obtained from testing undertaken during stationary condition of the shaft. When the shaft rotates, the dampers are subjected to rotating load that may affect their loss factor. The effect of shaft rotation on the loss factor is experimentally examined in this work. Impact test was used to determine the frequency response function (FRF) of the dampers. For the dampers subjected to rotating load, the loss factor values derived from the FRF was found to be in good agreement with those determined from the half-power bandwidth method. The results further showed that the loss factor at resonant frequency determined from testing of the dampers under stationary shaft condition underestimates the values of the loss factor when the shaft is rotating. The effect of shaft rotation on the values of the damper’s loss factor was more noticeable for the response in the X-direction as opposed to the Y-direction, indicating that pre-strain plays a more dominant role in influencing the loss factor of the dampers compared to the dynamic amplitude.

Enhancing Broadband Vibration Energy Suppression Using Local Buckling Modes in Constrained Metamaterials

Studies on dissipative metamaterials have uncovered means to suppress vibration and wave energy via resonant and bandgap phenomena through such engineered media, while global post-buckling of the infinitely periodic architectures is shown to tailor the attenuation properties and potentially magnify the effective damping effects. Yet, despite the promise suggested, the practical aspects of deploying metamaterials necessitates a focus on finite, periodic architectures, and the potential to therefore only trigger local buckling features when subjected to constraints. In addition, it is likely that metamaterials may be employed as devices within existing engineering systems, so as to motivate investigation on the usefulness of metamaterials when embedded within excited distributed or multidimensional structures. To illuminate these issues, this research undertakes complementary computational and experimental efforts. An elastomeric metamaterial, ideal for embedding into a practical engineering structure for vibration control, is introduced and studied for its relative change in broadband damping ability as constraint characteristics are modified. It is found that triggering a greater number of local buckling phenomena provides a valuable balance between stiffness reduction, corresponding to effective damping magnification, and demand for dynamic mass that may otherwise be diminished in globally post-buckled metamaterials. The concept of weakly constrained metamaterials is also shown to be uniformly more effective at broadband vibration suppression of the structure than solid elastomeric dampers of the same dimensions.

Frequency and Amplitude Dependent Dynamic Model of Rotor Elastomeric Damper with Refined Nonlinear Stiffness

Elastomeric damper is a very important component for helicopter rotor system; its dynamic property has strong nonlinear behavior characterized by complex hysteresis loops, and dependence on excitation frequency, amplitude and temperature. Based on internal variables theory, combined with the nonlinear spring model, a time domain nonlinear dynamic model of elastomeric damper used for helicopter rotor load prediction is presented. The model was characterized by using the genetic algorithm, the hysteresis loop of elastomeric dampers made of different elastomeric materials under several excitation frequencies and strain amplitudes was calculated with this model and compared with experimental data. It is shown that the presented model can predict the hysteresis loop of the elastomeric dampers with little relative errors, and the model is able to catch the variation of dynamic stiffness. Therefore, the presented method can be used for helicopter rotor load prediction and aeroelastic analysis.