Reorientation In Shape Memory Alloys Research Articles

Modeling of coupled phase transformation and reorientation in shape memory alloys under non-proportional thermomechanical loading

In the present study, a new 3D thermodynamic coupled model is proposed for SMAs. The behavior of SMA structures is described through several strain mechanisms, each associated with its proper internal variables. This model is built to capture the particular behavior of SMAs when subjected to complex loading, namely non-proportional thermomechanical loading. To achieve this task, a new approach to describe the martensitic reorientation mechanism has been introduced in conjuction with a new method to account for forward and reverse transformation. Thermomechanical coupling, related to dissipation and latent heat is fully implemented. The validity of the model is demonstrated by comparing experimental results of complex thermomechanical loading paths of SMA structures with numerical simulations.

Computational martensite re-orientation in shape memory alloys and the related hysteretic dynamics

In this paper, an approach based on the nonlinear theory of elastic dynamics is proposed to model microstructure evolution in a shape memory alloy patch. The hysteretic dynamics of the patch at the macro-scale is also modeled by employing Hamilton's principle. The elastic potential energy function is constructed as non-convex on the deviatoric strain, and the governing equations are formulated as two coupled wave equations in terms of the two displacement components. Square to rectangle transformations and rectangle variant re-orientations are modeled by simulating the transitions of system states from one stable branch of the non-convex constitutive relation to another. The proposed model allows a robust implementation of conventional finite element analysis with all typical boundary conditions, but with strong nonlinearity. Numerical results for microstructure evolution caused by boundary stress loadings are presented, laminated structures and needle-like microstructures, which are often observed in experimental investigations, are also obtained. Hysteretic dynamics at the macro-scale is presented together with microstructure evolution.

A three-dimensional phenomenological model for martensite reorientation in shape memory alloys

In this work, we propose a macroscopic phenomenological model that is based on the classical framework of thermodynamics of irreversible processes and accounts for the effect of multiaxial stress states and non-proportional loading histories. The model is able to account for the evolution of both twinned and detwinned martensite. Moreover, reorientation of the product phase according to loading direction is specifically accounted for. Towards this purpose the inelastic strain is split into two contributions deriving, respectively, from creation of detwinned martensite and reorientation of previously existing martensite variants. Computational tests demonstrate the ability of the model to simulate the main aspects of the shape memory response in a one-dimensional setting and some of the features that have been experimentally found in the case of multiaxial non-proportional loading histories. Experimental non-proportional loading paths have also been simulated and a good qualitative agreement between numerical and experimental response is observed.

Martensitic reorientation and shape-memory effect in initially textured polycrystalline Ti–Ni sheet

In this work we modify the crystal-mechanics-based constitutive model of Thamburaja [J. Mech. Phys. Solids, 53 (2005) 825] for martensitic reorientation in shape-memory alloys to include austenite–martensite phase transformation. Texture effects on martensitic reorientation in a polycrystalline Ti–Ni sheet in the fully martensitic state were investigated by conducting tensile experiments along different directions. By fitting the constitutive model to the stress–strain response for the experiment conducted along the 45° direction the constitutive model is shown to predict the experimental tensile stress–strain response in the rolling and transverse direction to good accord. Shape-memory effect experiments were conducted by raising the temperature of the post-deformed tensile specimens. Austenite–martensite phase transformation material parameters were first determined by fitting the model to a superelastic experiment. With the model calibrated, the experimental shape-memory effect stress–strain–temperature responses were reasonably well predicted by the constitutive model.

Thermo-mechanical modeling of the reorientation in shape memory alloys

Thermo-mechanical modeling of the reorientation in shape memory alloys