Study On Viscoelastic Damping Material And Dynamic Performance Of Its Special-shaped Interface Constrained Damping Structure

The special-shaped interface constrained damping structure composed of viscoelastic damping material and base layer and constrained layer was an effective way of vibration reduction and noise reduction of metro.Therefore,it was particularly important to research the dynamic performance of constrained damping structure.In this manuscript,the basic performance and damping properties of a new modified polyurethane viscoelastic damping material(hereinafter referred to as viscoelastic damping material)were analyzed,and the physical and damping characteristics of the material were analyzed.With this material as damping layer material,two kinds of special-shaped interface constrained damping structures,strip and sawtooth,were designed and fabricated.And the damping performance of constrained damping structures under two different structures was investigated by hammering vibration test.And then,the dynamic mechanical properties of the constrained damping structure had been investigated by using the method of finite element modal ANSYS corroborated with experimental results of vibration.And the influential factors of the structure s dynamic properties were discussed.This paper has three main research conclusions,as follows:Firstly,the basic properties and damping properties of viscoelastic damping materials showed that the density of viscoelastic damping mateCIals was 0.9529g/cm3.The gel time and the drying time were 158s and 14min respectively,and the solid content was 95.49%.The Shore A hardness was 38.The tensile strength and elongation at break were 1?10MPa and 564.94%respectively.And the viscoelastic damping material was a fast curing,high solid content,green,pollution-free material.On the same frequency,material storage modulus decreased with the increase of temperature,loss modulus and loss factor increased first and then decreased;On the same temperature,the higher the frequency was,the higher the storage modulus and loss modulus were,and the peak of loss factor also became larger.Secondly,the dynamic performance of strip type interface constrained damping structure was studied.It can be seen from the spectrum analysis that the first order loss factors of flat structures with different damping layer thickness were 0.037,0.144,0.223 and 0.276,respectively.With the increased of thickness,the loss factor increased by 0.107,0.079 and 0.053,but the range of increase decreased obviously.Compared with the flat structure,the loss factor of strip structure increased by 0.056,0.105 and 0.148,and the damping efficiency increased gradually.The octave spectrum analysis and time domain analysis showed that the vibration acceleration value and vibration duration were reduced effectively by increasing damping thickness and reducing strip width,so that the structure damping performance was improved.The composite loss factor which obtained by modal analysis of the finite element was very close to the results obtained in modal experiments,were between 0.037?0.497,the low order two errors are less than 10%,higher order error was slightly larger,but still less than 15%,which was in good agreement.Thirdly,the dynamic performance of sawtooth interface constrained damping structure was studied.It can be seen from the spectrum analysis that the vibration acceleration amplitude of the sawtooth structure with 120mm distance and 1mm damping layer was 2.25m/s2.This was the largest of the four structures.The vibration acceleration amplitude of the 4mm damping layer was 1.3m/s2.This was the smallest of the four structures.The vibration acceleration amplitude of the 2mm,3mm damping layer was 1.5m/s2.The damping layer was 2mm,sawtooth structure with different sawtooth spacing,the second single peak values were all around 0.25m/s2,while the second single peak values of flat structure were 1.75m/s2,which was about seven times of those of the other three.The octave spectrum analysis and time domain analysis showed that the total vibration level and vibration duration were reduced effectively by increasing damping thickness and reducing sawtooth spacing.Finite element analysis and modal experiment were in good agreement.By analyzing the influence of the constraint interface,it was found that both the natural frequency and the composite loss factor of the flat and sawtooth interface structure were smaller than those of the strip interface.The loss factor of seven units per unit area were 0.50 m-2,1.00 m-2,1.27 m-2,1.60 m-2,1.15 m-2,1.61 m-2,1.78 m-2,respectively.The loss factor per unit area of the flat interface was lower than that of the sawtooth and strip interface,with a maximum difference of 1.28 m-2.The sawtooth interface was lower than strip interface respectively,with a maximum difference of 0.31 m-2.Through the analysis of the influence of the boundary conditions,compared with simply supported constraints,the natural frequency of the structure of elastic support under the condition decreased,reduced to about 300Hz?600Hz;and the complex loss factor of the structure had different rate increase,the maximum increased about 0.3.Through the above theoretical analysis,analogue simulation and experimental study,the properties of viscoelastic damping materials and the main influencing factors of constrained damping structures of special-shaped interfaces were discussed,obtained the changing regularity of the structure's dynamic performance.It provided theoretical guidance for the application of constrained damping structures with special-shaped interfaces in vibration reduction and noise reduction projects.