SMA Material Property Analysis And Application Research In Building Seismic Isolation

As a new type of functional material with shape memory effect,super elasticity and high damping,shape memory alloy(SMA)has been gradually applied to the field of structural vibration control.In recent years,the world has experienced frequent earthquakes,and the footings of building structures have suffered serious deterioration of material mechanical properties under the action of high strain tension-compression cycle earthquakes,resulting in fatigue damage and structural destruction,causing serious casualties and huge economic losses.Therefore,it is urgent to explore the mechanism of building seismic isolation and to develop seismic isolation devices.In this paper,the Lowcycle fatigue performance of SMA bars with a diameter of 14 mm was studied,and the Low-cycle fatigue life prediction model of SMA bars is established;the response mechanism of building structures under earthquake action was revealed,and new SMA seismic isolation devices were developed based on the excellent energy dissipation and recovery performance of SMA bars.The work can be summarized are as follows:(1)To determine the optimal heat treatment conditions for SMA bars,firstly,the fatigue pre-test was conducted on the specimens after heat treatment at 350°C for 30 min,and the analysis of the energy dissipation and residual strain of the specimens revealed that the heat treatment conditions were not sufficient to improve the material properties,and the heat treatment conditions needed to be changed.Then,the specimens heat-treated at 400℃ for 15 min,30min and 45 min were subjected to tensile unloading test,and the stress-strain curves of the specimens were compared and analyzed,and the best heat treatment condition was found to be 400℃ for 45 min.(2)Determining the optimal strain amplitude for Low-cycle fatigue testing of SMA bars: Under the same heat treatment conditions,SMA bars were subjected to fatigue tests with strain amplitudes of ±2.5%,±3.5% and ±3.75%,and the test results showed that the larger the strain amplitude,the more obvious the mechanical properties of SMA bars;However,even when the strain amplitude was ±3.75%,the phase transition points of the specimens were still unclear and the hysteresis loop shape was still not full enough to analyze the mechanical properties adequately.Therefore,it was found that increasing the strain amplitude from ±3.5% to ±5.5% can make the stress-strain curves of SMA bars fuller and the mechanical behavior more obvious,so ±3.5% to ±5.5% is the optimal range of the strain value,which can provide test data to support the application in engineering.(3)In order to establish a low circumferential fatigue life prediction model for SMA bars,they were subjected to tensile-compression fatigue tests until fracture damage,and the fractures were analyzed by SEM.A theoretical basis is provided for fatigue life prediction of SMA bars under tensile-compressive loading.(4)Develop and design an SMA-steel seismic isolation device adapted to village buildings.Based on the fatigue damage of SMA bars and the structural damage mechanism under seismic action.The SMA bars were used as the main energy dissipation and reversible element of the seismic isolation device;the SMA seismic isolation device,SMA-steel bar isolation device and steel bar isolation device were developed.Then,numerical simulations are carried out to investigate their seismic isolation mechanism,SMA-steel bar isolation device were found to have both good seismic isolation performance and economy,which provides technical and theoretical support for the application of the SMA-steel bar isolation device.