A study of constrained-layer viscoelastic damping treatments and their application to flexible mechanisms

This dissertation presents an experimental and analytical study of constrained layer viscoelastic damping treatments. The first experiments were designed to prove the existence of compressive vibration in the viscoelastic core. These experiments showed that not only does compressive vibration occur, in violation of the fundamental assumption of the most common analytical models, but that the base and constraining layer vibrate with different mode shapes. This indicates that compressive vibration is not an isolated phenomenon but rather a damping mechanism that occurs to some extent for any frequency or loading condition.; Based on the experimental results, a new analytical model was developed assuming compressive vibration. Comparing experimental and analytical results showed that the compression model is a better predictor of resonance frequencies than the most popular shear damping models. In addition, an inconsistency in the definition of shear strain in the viscoelastic core was discovered in several of the most common shear damping models. Correcting this inconsistency resulted in a new shear damping model that was able to predict resonance frequencies with approximately half the error obtained from the popular Mead and Markus model. Damping predictions from both shear models were fairly good, generally within a factor of two, whereas damping estimates from the compression model were generally quite poor. The two new analytical models were then combined into a simple finite element model for the viscoelastic core in a constrained layer damping treatment.; Experimental tests were also performed on an operating damped flexible four-bar linkage. They showed that judicious application of damping treatments resulted in a 30% to 60% reduction in the steady-state coupler link response and a nearly complete attenuation of the start-up response. Subsequent finite element modeling was able to predict the steady-state dynamic response of the damped linkage to within a factor of four or better. This is quite remarkable, given the general difficulties in modeling a damped operating machine.