Issue 29

M. Marino, Frattura ed Integrità Strutturale, 29 (2014) 96-110; DOI: 10.3221/IGF-ESIS.29.10

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C ONCLUSIONS

A

novel constitutive model for the stress-induced martensitic transformations in SMAs has been proposed, accounting for: different behavior for the transformation laws of direct and reverse lattice rearrangement; asymmetric responses in tension and compression (both for transformation and stiffness properties); the possible co-existence of austenite, multi-variant and oriented martensites. Accordingly, the model is suitable for reproducing available experimental data on SMA pseudo-elastic properties. The model is formulated in a generalized energetic framework. By introducing a suitable pseudo-potential of dissipation and by formulating transformation-evolution laws from microscopic equilibrium equations, the fulfillment of the second law of thermodynamics is a-priori satisfied, without the need of implicit algorithms. In order to highlight this feature, the model is developed in detail within a fully explicit framework, easy to be implemented for computational analyses. Obtained results clearly show this feature, highlighting that material parameter identification is straightforward from experimental data, even accounting for a possible non-perfect pseudo-elastic behavior for SMA. The model has been here developed under the assumption of ideal non-hardening behavior. In upcoming works, it will be generalized in order to account for non-linear hardening effects, allowing for an effective comparison with experimental data. Moreover, shape-memory effects as well as non-isothermal response will be accounted for. Accordingly, the effects of non-linear transformation lines in the phase diagram, as well as of temperature-dependent transformation strains, on SMA mechanics will be shown. It is worth pointing out that, within present explicit framework and addressing non isothermal conditions, the value of / / d r    and / / D R    at the reference temperature T (at = t  ) can be considered in the governing equations at each incremental step. Accordingly, present model does not require to fix a specific form of interpolation functions for transformation lines in phase diagram (assumed piecewise-linear in most modeling approaches), as well as for the temperature-dependence of transformation strains, resulting in a very general and flexible tool for describing very different pseudo-elastic behaviors.

A CKNOWLEDGMENTS

T

he author gratefully acknowledges Prof. Franco Maceri, Prof. Giuseppe Vairo and Prof. Michel Frémond for fruitful discussions on this paper. This work was developed within the framework of Lagrange Laboratory, a European French-Italian research group. Present research study was supported by MIUR (PRIN, grant number F11J12000210001).

R EFERENCES

[1] Shape Memory Alloys. Modeling and Engineering Applications, Lagoudas, D.C. (Ed.), Springer Science+BusinessMedia, LLC, New York, USA, (2008). [2] Songa, G., Ma, N., Li, H.-N., Applications of shape memory alloys in civil structures. Engineering Structures, 28 (2006) 1266-1274. [3] Auricchio, F., Marfia, S., Sacco, E., Modeling of SMA materials: training and two way shape memory effects, Computers and Structures, 81 (2003) 2301-2317. [4] Auricchio, F., Bonetti, E., Scalet, G.,Ubertini, F., Theoretical and numerical modeling of shape memory alloys accounting for multiple phase transformations and martensite reorientation. International Journal of Plasticity, 59 (2014) 30-54. [5] Moumni, Z., Zaki, W., Son, N.-Q., Theoretical and numerical modeling of solid-solid phase change: Application to the description of the thermomechanical behavior of shape memory alloys, International Journal of Plasticity, 24 (2008) 614-645.

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