Research On The Constitutive Relationship Based On Grain Size For Shape Memory Alloys

Shape memory alloys(SMAs)attract extensive attention because of its temperature and stress sensitive properties,and SMAs are widely used in aerospace,mechanical,materials and other fields.Excellent biocompatibility,making it has a very important application in the field of biomedical.There exists stress hysteresis in loading and unloading cycle,lead to reducing the energy conversion efficiency of the material,which limits the application of materials.Therefore,it is necessary to explore the influence factors of the SMAs constitutive relationship on material properties.Based on the rate-independent constitutive model of elastic-plastic materials,a new constitutive model is proposed to describe the overall stress-strain relationship for phase transformation process of SMAs and to explore the effect of the grain size(GS)on the SMAs.In the paper,it is assumed that there is no plastic strain in the process of phase transformation,and regardless of the elastic deformation of martensite,it is considered that the elastic modulus of martensite is equal to the elastic modulus of austenite in the martensitic elastic unloading stage.On this basis,a numerical simulation is carried out,It is shown the proposed model can represent the stress-strain relationship of SMAs effectively.The yield stress increases with the reduction of grain size.The superelastic stress-strain hysteresis loop area(H)of the polycrystal decreases with the GS and the phase transition strain decreases as the grain size decreases either.All theoretical results agree with the experiment data.