Research On Mechanical Properties Of Shape Memory Alloy Microstructure

Smart material is a new kind of functional materials,and the properties of materials will change significantly under the influence of excitation.Among the existing smart materials,shape memory alloy(SMA)has excellent comprehensive performance,shape memory effect and super elasticity,high energy density,high driving frequency,and large output stress and strain.Various microstructures prepared from shape memeroy alloy are widely used in aerospace,medical,industrial and micro-electromechanical systems and other fields.Whether the micro-structure performance is good depends largely on the mechanical properties of the shape memory alloy micro-structure,therefore,it is very important to study the mechanical properties of shape memory alloy micro-structure.Functional Graded Shape Memory Alloy(FG-SMA)can effectively alleviate the hysteresis effect of shape memory alloy,and micro-beam is the most widely used in micro-structure,therefore,the research on the nonlinear free vibration and resonance response characteristics of thermo-mechanical-electric multi-field coupled FG-SMA micro-beam is of great significance for promoting the wide application of new FG-SMA composite.In this study,the dynamic performance of FG-SMA micro-beam was studied by combining theoretical analysis and simulation.The main research contents are divided into the following points:(1)A thermo-mechanical-electric multi-field coupled nonlinear mechanical model of clamped-clamped FG-SMA micro-beam with size effect is established.Considering the effects of electric field force,intermolecular Casimir force and temperature change,based on von Carmen's geometric nonlinearity theory,the modified strain stress theory and displacement are used to obtain stress and strain,and based on the Hamilton principle,the governing equations of the nonlinear free vibration and resonance response of FGSMA micro-beam are derived.Finally,the Differential Quadrature Method(DQM)is used to solve the nonlinear free vibration governing equations,and the average method is used to solve the resonance response governing equations.(2)Investigate the dynamic mechanical characteristics of FG-SMA micro-beam model.Analyze the influence of dimensionless size effect parameters,volume fraction index,slenderness ratio,fixed electrode surface shape parameters,gap ratio,temperature and its change,intermolecular Casimir force,quality factor,DC component and AC component amplitude of excitation voltage on dynamic characteristics of micro-beam model.Solve the dynamic pull-in instability voltage and first-order nonlinear characteristic frequency of the corresponding parameters of the micro-beam,study the nonlinear free vibration characteristics of the micro-beam;solve the plot of the amplitudefrequency characteristics and phase-frequency characteristics of the corresponding parameters of the micro-beam,and study the resonance response characteristic of the micro-beam.(3)Based on the solved stress-strain relationship and control equation of the FGSMA microbeam,the multiphysics simulation software COMSOL was used to create a three-dimensional model of the FG-SMA micro-beam,which was compared with the theoretical solution and verified to analyze the influence of each parameter,and further study FG-SMA micro-beam dynamic characteristics.