Investigation On Polyurethane Damping Material And Constrained Damping Structure

Polymer damping materials play an important role in vibration structures. It has many advantages like inexpensive, high loss factor, lightweight and so on. Usually, a vibration structure containing polymer damping materials which called free-layer damping or constrained layer damping structure can achieve higher structure loss factor. The aim of this paper is to investigate the static and dynamic mechanical properties of a damping material based on polyurethane, and analyze the effect of thickness of the material on the structure loss factor of constrained layer damping structure.The tensile machine was used to test the shear modulus and strength of the damping material at 45mm/min at 15℃.Also, the factors such as molecular structure and internal morphology of the material had been studied. The 90°peeling off experiment was performed at 45mm/min at 15℃.Its failure mechanism had been analyzed.The Differential Scanning Calorimetry experiment was chosen to achieve the material glass transition temperature zone and its thermodynamic stability. In the experiments, it shows that the material's glass transition temperature zone is between-25℃and-20℃.It also shows that the material at 120℃isn't melt and decomposed.The Dynamic mechanical analysis was used to analyze dynamic mechanical properties like dynamic storage modulus, dynamic loss modulus and material loss factor from-40℃to 100℃. The influences of temperature on the dynamic mechanical properties of the material were studied. The results show that at 1Hz, the material's glass transition temperature is-16℃. The material loss factor increases to a peak (0.97) at glass transition temperature and its loss modulus rises up to a peak (99 MPa) at-27℃. Then, with the increasing temperature, they begin to descend. It also shows that the material storage modulus reduces from 350MPa to 0.5MPa as the temperature increases from-40℃to 100℃. The movement of molecule chains has been exacerbated and the free volume in material gets larger when the temperature increases, so that the dynamic storage modulus decreases dramatically with the increasing temperature. Intermolecular forces increase when the temperature rises from-40℃to-27℃, and then decrease when the temperature increases, so that the dynamic loss modulus exhibits a peak at-27℃and then decrease.The cantilever beam test was used to study the effect of frequency on material dynamic properties. The result shows that at 13℃, material loss factor increases to a peak (0.77) at 570Hz as the frequency increases. Then, over this frequency, it begins to descend. It also shows that material storage modulus enhances from 0.8MPa to 2.5MPa when the excitation frequency keeps rising. The influence of frequency on dynamic properties of the material is correlated to the material relaxation time.The dynamic results according to the cantilever beam test show that the resonant frequencies for vibration modes decrease with the increase of polymer layer thickness and drop drastically at higher vibration modes. When the damping layer thickness increases from 0.91mm to7.96mm. the resonant frequency drops from 141 Hz tollOHz at mode 1, simultaneity drops from 846 Hz to649Hz at mode 2, and 2291 Hz to 2149Hz at mode 3.This is because the increase of polymer layer thickness reduces the reference frequencies and the degree of the vibration coupling between matrix layer and constrained layer, and enhances the system stiffness. The system resonant frequencies decrease when the reference frequencies or the degree of the vibration coupling lower. At the same time, the system resonant frequencies increase when the system stiffness gets lager. Though the degree of the vibration coupling and the system stiffness were very less effective in this experiment. system resonant frequencies were mainly determined by the reference frequencies.Furthermore, the cantilever beam test results also show that the system loss factor increases drastically when the viscoelastic layer is thicker. As the damping layer thickness increases from 0.91mm to7.96mm, the system loss factor increases from 0.0595 to 0.179 at mode 1, simultaneity increases from 0.027 to 0.0996 at mode 2, and 0.0193 to 0.0305 at mode 3. According to Kerwin's theory, the thicker the polymer layer the higher the system stiffness, and the thicker the polymer layer the lower the degree of vibration coupling between matrix layer and constrained layer. The system loss factor increases when the system stiffness gets higher, and reduces when the degree of vibration coupling gets lower.