Study On Dynamic Mechanical Properties Of Viscoelastic Materials And Damping Structure

The viscoelastic damping treatment of structure has becoming an important method in controlling the resonant vibration responses and the radiating noises of mechanic structures. However, multiple target design of damping structure, improving the damping performance of structure is the key technology problem. Therefore it is necessary to study the dynamic mechanical properties of viscoelastic damping materials (VEM) and the relation between VEM and its additional damping structure. Dynamic mechanical properties of VEM were studied with dynamic mechanical analysis (DMA) and cantilever beam resonance method. It was also analysed that how temperature and frequency effect dynamic mechanical properties of VEM. Besides this paper also verified the effectiveness of finite element method based on GHM model to describe constrained damping structure modal parameters. The influences of viscoelastic damping on the dynamic properties of several selected typical structures were investigated with experimental modal analysis method and wide-frequency vibration analysis method. The influence on reducing the resonant and wide-frequency vibration response of additional damping form(free damping or contrained damping), material damping property, thickness of damping layer, stucture of damping treatment was studied. The conclusions as follows:First, the DMA test results indicated that the loss factor peak of VM-1, VM-2, VM-3were respectively0.82,0.87,0.76, and the glass transition temperatures were-20℃,15℃and40℃. VM-3contrast analysis results of DMA and cantilever beam resonance method showed that:the elastic modulus measured at various temperatures with two methods were much too different. In addition the loss factors measured were quite close. At30℃, the goodness of fit of elastic modulus was79.47%, and the goodness of fit of loss factor was96.94%. While the elastic modulus and loss factor of viscoelastic damping materials with two methods in the high frequency domain matched well. At the frequency of380.50Hz, the goodness of fit of elastic modulus is96.11%, and the goodness of fit of loss factor is90.51%. Based on experimental results above, through the reduced variable method, the paper obtained the master curve of viscoelastic damping materials, established the numerical and prediction model of viscoelastic damping materials dynamic mechanical properties, determined the model parameters, and study some basic laws of viscoelastic damping materials dynamic mechanical properties.Second, An improved finite element analysis (FEA) method based on GHM model was used to investigate the dynamic properties of a viscoelastic constrained damped beam with the consideration of frequency-dependent property of damping materials. The first four order resonance frequency proportional error are respectively1.52%,3.34%,7.19%,2.88%, The calculated resonance frequency results agreed well with modal test results, which shows that the FEA method is reliable and relatively accurate. loss factor calculated GHM model and that measured by experiment differed large, especially at low frequency, which were caused by the large amplitude nonlinear vibration of the cantilever beam.Third, the rule and effect of damping treatment (free damping and constrained damping method) on the cantilever beam and end clamped steel plate agreed:The resonance frequency of free damping treatment structure was lower than no damping structure, while that of constrained damping structure was higher than no damping structure, and the loss factor of damping treatment structure went up. The second order loss factors of no damping, free damping and constrained damping structure cantilever beam were0.032,0.053,0.180. The second order loss factors of VM-1, VM-2, VM-3damping concrete sandwiches were0.032,0.053,0.180. concrete sandwiches with damping layer thickness of1mm,2mm,3mm and4mm were0.145,0.245,0.321,0.345. the second order loss factor of A-type structure, B-type structure, C-type concrete sandwiches were0.245,0.265,0.281, with the enhancement of damping layer shearing action, structure loss factor grew.Finally, compared to free damping structure, constrained damping structure plate vibration reduced more significantly, especially at the center frequency of63Hz and200Hz vibration acceleration level of1/3octave analysis reached over30dB. The vibration acceleration total level value of free damping, constrained damping structure plate reduced by0.98dB,26.42dB.Different viscoelastic damping materials have a direct mrpace on the constrained damping structure damping performance. The total; vibration acceleration level value of VM-1, VM-2, VM-3concrete sandwich decreased by2.67dB,4.58dB,7.42dB, the damping performance of VM-3was outstanding out of the three kinds of viscoelastic damping materials. The damping effect of concrete sandwich intensified with the increment of damping layer thickness. The total vibration acceleration level value of concrete sandwich with lmm,2mm,3mm,4mm thickness of damping layer decreased by4.98dB,7.42dB,9.86dB. Through the structure optimization design could improve the damping performance of constrained damping structure. The total vibration acceleration level value of A-type structure, B-type structure, C-type structure concrete sandwich lowered by7.42dB,8.65dB,10.86dB. At higher frequency (500-3150Hz), vibration attenuation was more obvious, in the entire analysis frequency, B-type structure and C-type structure vibration attenuation is greater than A-type structure.According to the above experimental study and theoretical analysis, some measures can be gained to study the relationship of viscoelastic damping materials dynamic mechanical properties and structure damping performance, which provide basic data and theories for the damping structure optimization design.