Research On Mechanical Properties Of SMA Microbeams With Thermo-mechanical Coupling Considering Surface Effects

Shape Memory Alloys(SMA),as a new type of smart material,has attracted extensive attention because of its superelasticity and shape memory effect.Research shows that the main two properties of SMA materials,stress and temperature,have a direct impact on each other.This paper uses the method of numerical simulation that is based on the SMA constitutive model,Euler-Bernoulli beam theory and Gurtin-Murdoch surface elasticity theory to study the coupling characteristics of thermal and mechanical of SMA micro beam with surface effect.The main research content is as follows:(1)Considering surface effects,simplify and establish a SMA micro-beam mechanical model based on the plane assumption of Euler-Bernoulli beam theory and Gurtin-Murdoch surface elasticity theory.Then we analyze the influence of the surface effect on the bending mechanical properties of the micro-beam when the size of the micro-beam section changed,and further analyze the influence of the tensioncompression asymmetry coefficient on the stress distribution of the SMA micro-beam section when the surface effect was considered.(2)On the basis of analyzing the influence of temperature on the critical stress and thermal strain of SMA,we establish a mechanical model of thermally coupled SMA microbeams when considering surface effects to study the mechanical properties of SMA microbeams under the effects of the coupling of temperature-changing and bending moment.Analyzed the effects on the offset of the neutral axis as well as the strain and stress distribution of the section of the microbeam when the bending moment and temperature changes.Then study the effects of residual surface stress and surface elastic modulus on the mechanical properties of SMA microbeams when considering surface effects.(3)According to the Voigt theoretical model and the mechanical theory of composite materials,a functionally graded shape memory alloy(FG-SMA)microbeam mechanical model considering the change of temperature and the tension-compression asymmetry coefficient as well as surface effects was established.Then we analyze the effects of material parameters,geometric parameters,and applied loads on the bending mechanical properties of FG-SMA microbeams,and compare the results with those are related to the mechanical properties of microbeams without considering the surface effect.