Studies On Constitutive Relations And Mechanical Properties Of Porous Ferromagnetic Shape Memory Alloy Considering Magneto-Thermo-Mechanical Coupling

Porous Ferromagnetic Shape Memory Alloys(porous FSMA)is a new type of intelligent driving and sensing material with many advantages,such as magnetic induced large strain,high energy output,fast response frequency and porosity.In this thesis,the mechanical-magnetic coupling behaviors and thermal-mechanical-magnetic coupling behaviors of martensitic reorientation of porous ferromagnetic shape memory alloy under external magnetic field,stress and temperature are theoretically analyzed and numerically simulated.Firstly,based on the micromechanics,Eshebly theory and Mori-Tanaka field average method,the constitutive relation of porous FSMA is produced.In the deduction process,the influence of disturbed strain is ignored,and the martensitic variant induced by magnetic field and pores are embedded into the corresponding stress-induced martensitic variant of infinite matrix as inclusion phase,Thus,the three-phase micromechanical constitutive model of porous shape memory alloy under magneto-mechanical coupling is established.Then,the hyperbolic tangent function is used to describe the volume fraction of the reorientation process of martensitic variants.By selecting the internal state variables to describe the reorientation process of materials,the reorientation behaviors of porous FSMA under the magneto-mechanical coupling are described.The constitutive model of porous ferromagnetic shape memory alloys is degraded to solid state,which is compared with the experimental research.The results show that this model can well characterize the magneto-mechanical behavior of the reorientation and reverse orientation process of martensitic variants in the material,so as to discuss the mechanical properties of porous FSMA under different porosity,magnetic field and stress.Secondly,the three-phase thermodynamic constitutive model of porous ferromagnetic shape memory alloy is established from the above micromechanics point of view.Based on Eshebly equivalent inclusion principle and Mori-Tanaka field average method,considering the influence of material disturbance strain,the stress-strain relation of porous ferromagnetic shape memory alloy under thermal-magneto-mechanical coupling is derived,The effective elastic model of porous ferromagnetic shape memory alloy and the full expression of inelastic strain are obtained.Finally,according to the principle of thermodynamic equilibrium,the generalized driving force and the thermodynamic equilibrium equation of reorientation of martensite variant are obtained.The stress-strain behavior and magnetic-induced strain behavior of porous ferromagnetic shape memory alloy in the reorientation process of martensite variant are analyzed.Considering the influence of temperature on the reorientation process,the reorientation behavior of porous ferromagnetic shape memory alloy under thermalmagneto-mechanical coupling is obtained.To sum up,the three-phase micromechanical constitutive model of porous ferromagnetic shape memory alloy under magneto-mechanical coupling and thermal-magneto-mechanical coupling are given in this thesis,which can provide theoretical guidance for the further research and application of porous ferromagnetic shape memory alloy materials in aerospace,biomedicine and other fields.