Research On The Mechanical Behavior Of Shape Memory Alloy Spring

Shape memory alloy has been widely used in various fields due to its excellent super-elastic properties and shape memory effect.The shape memory alloy spring combines the basic properties of material and the flexibility of spring structure,which has been used as a vibration damping and energy dissipation element.In this paper,the loading-unloading experiments of shape memory alloy spring under different displacement amplitudes are firstly carried out.The mechanical deformation behavior of this type of spring is revealed.Then,the 3D thermal-mechanical coupled cyclic constitutive model of shape memory alloy established by Yu et al.is simplified and improved.Combined with spring theory,the isothermal spring model is extended to the thermal-mechanical coupling situation,and a theoretical model describing the static behavior of shape memory alloy spring is established.At the same time,the finite element transplantation of the improved constitutive model was completed,and the finite element calculation was carried out.Further,the experimental,numerical simulation and finite element analysis results are compared,and the effects of different geometric parameters on the static response of the shape memory alloy spring are predicted.Finally,based on the statics calculation,the dynamic response of the shape memory alloy spring under different external loads is analyzed,and the relationship between the geometric parameters of the shape memory alloy spring and the shock absorption and energy dissipation characteristics is explored.The research results in this paper can be used as a theoretical reference for the design and performance optimization of shape memory alloy spring.The specific research contents and results are as follows:(1)Carry out loading-unloading experiments with different displacement amplitudes of shape memory alloy spring to reveal the deformation behavior of such spring.Aiming at the phenomenon that the critical stress of shape memory alloy inverse transformation decreases with the increase of strain amplitude,and considering the convenience of constitutive model in engineering application,the cyclic constitutive model established by Yu et al.is simplified and improved.The evolution equations for hysteresis loop width and transformation hardening are modified to describe their relationship to the martensite volume fraction at the onset of reverse transformation.In the deformation of the spring,considering the effects of torque and bending moment on the spring section,as well as the spring temperature evolution caused by the heat generation of the shape memory alloy phase transformation,the classical isothermal spring theory is extended to the thermal-mechanical coupling case.Combined with the improved constitutive model and the extended spring theory,a theoretical model to describe the static behavior of shape memory alloy spring is established.At the same time,the improved constitutive model is transplanted into finite element,and written into the ABAQUS user material subprogram UMAT,and the finite element model describing the shape memory alloy spring is established.(2)According to the established theoretical model and finite element model,the static analysis of the shape memory alloy spring is carried out.By comparing the experimental,theoretical and finite element results,the correctness of the improved constitutive model and the developed spring theory is verified.Furthermore,the effects of different geometric parameters on the static response of shape memory alloy spring are predicted.(3)On the basis of static analysis,the dynamic response of shape memory alloy spring is explored.A shape memory alloy spring oscillator system is established,and the dynamic response of the system under free vibration,sinusoidal excitation and seismic load(random load spectrum)is analyzed under the control of no control,damping control,shape memory alloy spring and magnesium alloy spring.Furthermore,the influence of the geometric parameters of the spring on its shock absorption and energy dissipation performance under the action of seismic load is analyzed.