Research On Mechanical Properties And Finite Element Modeling Of The Bolt With A Shape Memory Alloy

As one of the most important connection forms,bolt connection is widely used in the structural design of key connecting parts of aerospace equipment.Bolts tend to loosen when subjected to impact,vibration,or cyclic loading,and at certain stages lead to the attenuation of clamping force and subsequent failure of connection,which can lead to catastrophic consequences for critical safety components.Therefore,the research on mechanical properties of bolted joint has become a significant research topic.Shape memory alloy(SMA)has become one of the important research directions because of its super elastic effect and shape memory effect.Shape memory alloy(SMA)has become one of the important research directions because of its superelastic effect and shape memory effect.Due to the nonlinearity and martensitic transformation of the superelastic SMA bolts,the accumulation of unrecoverable deformation will occur in the stress concentration of the thread root,which will have an important effect on the mechanical properties of the bolts.In order to maintain the engineering value of superelastic SMA bolt,the mechanical properties of superelastic SMA bolt fasteners were studied through experiment and theoretical modeling.The main work is as follows: 1.The concept of shape memory alloy and the mechanism of microstructure transformation were studied.According to the widely used SMA constitutive model,the relationship between martensite content and stress was introduced by Brison to establish a macroscopic phenomenological constitutive model that can completely describe the uniaxial phase transition of superelastic SMA bolt materials.2.Mechanical properties experiment of superelastic SMA bolted joint were tested,and the experimental platform for cyclic loading of superelastic SMA bolt was built,the rule of the macro mechanical response of the bolt is obtained.Meanwhile,the martensitic phase change point and microstructure of the bolt were detected by differential scanning calorimetry,scanning electron microscope and XRD diffractometer.The evolution law of microstructure of thread root is obtained.Results show that the greater the load value of pre-tightening force and the cyclic loading,the greater the attenuation amplitude clamping force on the bolt.With the increase of loading cycles,the continuous accumulation of martensite residual strain is the main reason for the significant attenuation of clamping force.The attenuation mechanism of clamping force of ultra-elastic SMA bolts was further verified and elucidated by the evolution of residual martensite morphology at thread root under different stress levels.3.According to the need of programming nonlinear beam element,the nonlinear stiffness matrix of beam element is derived by using finite element method,and the solving principle of nonlinear beam element program algorithm is introduced.And the MATLAB language is used to write the program algorithm which can be used to solve the nonlinear beam element.The model of bolted joint based on superelastic SMA beam element is established,the finite element numerical method of the bolt under the action of external load is studied,and the numerical model is constructed for the mechanical numerical simulation of superelastic SMA bolt.The results show that the finite element model method for super elastic SMA bolts established in this paper is in good agreement with the experimental results and consistent with the actual,and experimental results is consistent with the actual and can effectively analyze and calculate the mechanical properties of superelastic SMA bolts.