Research On Seismic Performance Of Sector Viscoelasticity Damper Based On NMK/FKM Nanocomposite

The frame structure system is a widely used and promising building structure system with good stiffness and strength,which can effectively resist seismic forces under earthquake action.However,in the case of strong earthquakes,frame nodes are prone to failure,which can have a negative impact on the stability of the entire structure.In order to improve the seismic performance of frame structures,viscoelastic dampers are widely used as node energy dissipation devices to reduce the damage of earthquakes to the structure.Viscoelastic dampers mainly rely on high damping rubber materials to achieve their shock absorption effect.Therefore,the performance of rubber materials is a key factor affecting the seismic reduction and isolation performance of viscoelastic dampers.In this study,nano metakaolin(Nano Metakaolin,NMK)was used as filler to modify fluororubber(fluororubber,FKM)by melt blending to prepare a new type of NMK/FKM nanocomposite.And the physical and mechanical properties,dynamic mechanical properties,vulcanization performance,flame retardancy,and micro mechanism of the composite material were analyzed through uniaxial tensile test,DMA test,vulcanization test,oxygen index test,and XRD test.At the same time,based on material performance test data,the composite material is used as an energy dissipation material,and a sector shaped viscoelastic damper based on NMK/FKM composite material is proposed.A systematic study was conducted on the seismic energy dissipation performance of a new composite viscoelastic damper using finite element simulation method.The main work content and conclusions are as follows:(1)Through static tensile and DMA tests,it was found that the hardness and tensile strength of NMK/FKM nanocomposites increased with the increase of NMK/FKM ratio,reaching their maximum values at a ratio of 20/100,at 75 Shore A and 12.8MPa,respectiv ELy.At the same time,the elongation and permanent deformation of composite materials show a decreasing trend.During the process of increasing the NMK mass fraction,the quantified values of the loss factor and glass transition temperature of the composite material first increase and then decrease,reaching their peak at a ratio of 20/100,at 1.40 and 13.79 ℃,respectively.In addition,when the temperature is greater than 20 ℃,the loss factor of the composite material is always greater than 0.5,indicating that the damping temperature range of the composite material has been effectively expanded.(2)The vulcanization test and oxygen index test showed that the addition of NMK shortened the scorching time t0 to varying degrees,improving the vulcanization reaction rate of the composite material;The ultimate oxygen index of composite materials is greater than 30%,and the ignition self extinguishing behavior is significant,proving that composite materials have excel lent flame retardancy.(3)XRD testing observed the micro morphology of the composite material on the one hand,and analyzed the micro crystal structure of the material on the other hand,and analyzed the mechanism of the performance changes of the composite material at the micro level.NMK molecules crosslinked and strongly interacted with fluororubber macromolecules in the form of flakes or scales.Nanoscale NMK materials optimized the crystal structure of the rubber matrix and changed the grain size,Thus,the performance of composite materials has been improved.(4)The dynamic shear performance of a sector shaped viscoelastic damper with NMK/FKM nanocomposites as the viscoelastic material layer was simulated using ABAQUS finite element software under 144 loading conditions.The effects of material layer thickness,loading frequency,and strain amplitude on the working performance,energy dissipation performance,structural parameters,and structural stress distribution of the damper were studied.The results show that the hysteresis curve of the damper is symmetrical and full,with strong energy dissipation and deformation capabilities,and stable energy dissipation performance.As the thickness of the viscoelastic layer increases,the performance parameters of the damper continue to decrease.At small strain amplitudes,the characteristic parameters of the damper are less affected;As the strain amplitude increases,the maximum load,hysteresis loop area,energy dissipation coefficient,and equivalent damping ratio of the damper continue to increase.At four different loading frequencies,the maximum load variation of the damper is relatively small.The higher the frequency,the greater the energy dissipation coefficient and equivalent stiffness of the damper,and the equivalent damping ratio gradually decreases.(5)A single span four story reinforced concrete frame structure was designed based on the finite element software ABAQUS.The original structure and the energy dissipation structure installed with NMK/FKM composite material sector viscoelastic dampers were subjected to time history analysis of different seismic acceleration peaks under three different seismic waves.The results show that as the seismic acceleration increases,the characteristic parameters of the structure such as interlayer displacement angle,vertex acceleration,vertex displacement,and column bottom shear force also increase;The NMK/FKM composite material damper has a good energy dissipation and vibration reduction effect on reinforced concrete frames,effectively reducing the interlayer displacement angle,vertex acceleration,and vertex displacement of the structure,and also has a certain control effect on the column bottom shear force;The damper is superior to velocity response control in controlling the seismic displacement response of the structure,and its constraint effect on the structural vibration response is particularly significant at high acceleration peaks,effectively improving the structural energy dissipation and vibration reduction performance of the frame structure under earthquake action.