Non-local modeling on macroscopic domain patterns in phase transformation of NiTi tubes

【摘要】：正Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading.The new phenomena include deformation instability with the formation of a helical domain,domain topology transition from helix to cylinder,domain-front branching and loading-path dependence of domain patterns.In this paper,we model the polycrystal as an elastic continuum with nonconvex strain energy and adopt non-local strain gradient energy to account for the energy of the diffusive domain front.We simulate the equilibrium domain patterns and their evolution in the tubes under tensile loading by a non-local Finite Element Method(FEM).It is revealed that the observed loading-path dependence and topology transition of domain patterns are due to thermodynamic metastability of the tube system.The computation also shows that the tube-wall thickness has a significant effect on the domain patterns:a large tube-wall thickness leads to a long and slim helical domain and a severe branching of the cylindrical-domain front.