Characterization Of Viscoelastic Damping Material And Damping Properties Of Constrained Damping Structure

This paper is baced on the specialties of Qingdao building underground subwaysystem, which consisting of driving environment, geological and geographicalenvironment, material selecting for vibration and noise reduction of rail, as well as thestructural characteristics of vibration and noise reduction. Both polyurethane andmodified polyurethane viscoelastic materials are characterized and the dampingproperties of their constrained damping structure are studied, and a comparativeanalysis of the two structure are conducted, and its analysis results show below:(1)The characterization of polyurethane and modified polyurethane viscoelasticdamping material is mainly researched in terms of drying time, solid content, hardness,mechanical and damping properties.Study results indicate that the gel time and dryingtime of Modified polyurethane viscoelastic damping material is22s and49minrespectively and shorter than which of polyurethane viscoelastic damping material55sand4h. The solid content of polyurethane and modified polyurethane viscoelasticdamping material is99.34%and99.11%respectively, and they meet environmentalfriendly standards. The hardness of the above materials is17and29(Shore A)respectively, they are soft. Mechanical properties of the modified polyurethaneviscoelastic damping material is poor than polyurethane viscoelastic damping material,the tensile strength and elongation at break of the latter is only65%and88%of theformer. While ambient temperature is25℃and the vibration frequency between5~50Hz, the loss factor of polyurethane and modified polyurethane viscoelastic dampingmaterial increasing as frequency increases, but the latter is always larger than theformer, such as at frequently of50Hz,the loss factor of the above material is0.6427and0.8934respectively.(2) The factors influencing damping properties of constrained damping structure,mainly including damping layer thickness, constraint layer stiffness ambienttemperature are discussed.The results of the study show that: in the research of damping layer thickness range (1mm、2mm、3mm、4mm), the damping layer whosethickness of1mm, the properties of both polyurethane and modified polyurethaneconstrained damping structure is the best, the complex damping loss factor of first twonatural frequencies for the latter are1.2064and0.9324, respectively is1.25times and3.2times of the former; In the16~3150Hz frequency range, the total vibrationacceleration level of modified polyurethane constrained damping structurerespectively for88dB,2.14dB less than the non-modified one; The largest of thevibration acceleration vibration amplitude and the decay of the time were399.744mm/s~2and0.015s for modified polyurethane, respectively157.557mm/s~2and0.008sless than the former. In the range of the stiffnesses which have been studied, thedamping properties of both polyurethane and modified polyurethane constraineddamping structure increase damping layer with constraints reduce with the increase ofthe stiffness, and in the same stiffness of constraint layer and base material, dampingproperties of modified polyurethane constrained damping structure is always betterthan polyurethane. In the temperature range of-70℃~90℃. the loss factor ofpolyurethane and modified polyurethane viscoelastic damping materials increase atfirst and decrease latter with the rise of temperature,and the former reach a peak valueof1.3286at16.5℃and the latter gain a loss factor maximum of0.9151at30.5℃.In the temperature range studied. When ambient temperature is25℃, polyurethaneand modified polyurethane viscoelastic damping materials damp best, and at the firstorder of complex loss factor are respectively0.6231and0.7187, and the second orderare separately0.2607and0.3706; The vibration acceleration level of polyurethaneand modified polyurethane constrained damping structure vibration are respectively90.02dB and87.13dB, which are7.45dB~14.35dB less than other temperatures;Inthe temperature of25℃, the vibration acceleration amplitude is the smallest of othertemperature, and its values are respectively622.8mm/s~2,285.933mm/s~2.Through the polyurethane and modified polyurethane viscoelastic damping materialsof the above were studied and the effect factors of their constrained damping structure were researched，the data support which the viscoelastic damping materials andconstrained damping structure were applied in the project provided by the researchresults.