Analysis Of The Phase Transformation Mechanical Behaviour Of Shape Memory Alloy Beam With Variable Cross Section

Shape memory materials are a class of smart materials whose unique properties include shape memory effects and superelasticity.Among them,Ti Ni shape memory alloys are the most widely used materials and have been innovatively applied in the fields of sensors,actuators,robotics,aerospace,civil engineering and medicine,etc.The shape memory effect and superelasticity of Ti Ni shape memory alloys originate from the martensitic phase transformation that occurs inside the material,and their unique mechanical behavior affects the structure.In order to fully utilize the material properties and develop and design new structures and devices made of Ti Ni shape memory alloy,the factors affecting the structure during phase transformation of shape memory alloy need to be studied in depth.This paper focuses on the asymmetric bending of shape memory alloy variable-section beams and shape memory alloy box-section beams under mechanical loading,as well as the buckling and postbuckling of shape memory alloy rods under mechanical loading.Firstly,based on the bending deformation theory,the nonlinear control equations of shape memory alloy variable-section beams are derived by combining the existing intrinsic structure relations of shape memory alloys,and the phase change mechanical behavior of variable-section beams during bending deformation is analyzed by using a phased step-by-step approach,and the effects of mechanical load,tensile and compressive asymmetry coefficients and variable-section coefficients on neutral axis displacement,curvature and phase boundary are obtained and compared with the finite element The results were compared with the finite element results,and the results were in good agreement.Next,the effects of box thickness on neutral axis displacement,curvature and phase boundary were investigated by applying concentrated load to the box section beam of shape memory alloy.The two geometrical structural factors of variable section and box section are also combined to analyze the variation law exhibited in the phase transformation process of shape memory alloy under complex structure,and the results show that the change of box thickness will have a significant effect on the phase transformation process.Finally,the unique buckling and post-buckling behaviors of superelastic shape memory alloy rods are analyzed by numerical simulations to explore the effects of phase transformation behavior and length-to-thin ratio on the critical load.The load-deformation curves of the rod during loading are predicted using the finite element method,and the stress distributions of the rod in the tensile and compressive sides under different loading conditions are calculated.The results show that the stresses and strains under the influence of phase change will show different development trends.