Transformation yield surface of nanocrystalline NiTi shape memory alloy

Molecular dynamics (MD) simulation is used for investigating mechanical behavior and phase transformation in nanocrystalline NiTi shape memory alloy (SMA) under complex stress states, including uniaxial, biaxial and triaxial stress states. The simulation results indicate that tension-compression asymmetry occurs in terms of transformation strain, critical transformation stress, dissipation energy density, martensite variant and martensite domain. This asymmetry is mainly aroused by the fact that transformation strains under the stress states with tensile loading in the major deformation direction are larger than the counterparts under the stress states with compressive loading in the major deformation direction for most crystallographic orientations. The phase transformation stresses in complex stress states strictly comply with neither the Von Mises criterion without considering tension-compression asymmetry nor the Bouvet and Patoor criteria considering tensioncompression asymmetry. Consequently, a new transformation yield criterion on the basis of Bouvet and Patoor criteria is proposed in the present work to precisely describe the transformation stress anisotropy of nanocrystalline NiTi SMA under complex stress states.

Automated summary

The mechanical behavior and phase transformation of nanocrystalline NiTi shape memory alloy under complex stress states were investigated using molecular dynamics (MD) simulation. Tension-compression asymmetry was observed in terms of transformation strain, critical transformation stress, dissipation energy density, martensite variant, and martensite domain. A new transformation yield criterion based on the Bouvet and Patoor criteria was proposed to accurately describe the transformation stress anisotropy in complex stress states.