Abstract. Many materials are concerned by strain localization, for instance PLC phenomena, Lüders' bands or Shape Memory Alloys (SMA). The experimental identification of such material behaviors requires the use of full field kinematic measurements, such as provided by Digital Image Correlation (DIC), as well as Infra-Red (IR) thermography to evaluate the associate thermal dissipation. Jointly, these field measurements allow for a full thermo-mechanical characterization of material behavior. However, the space and time association of both fields remains a major difficulty (antagonist surface texture requirements, imaging devices having different pixel number and acquisition rate...). In this paper, we introduce a much simpler experimental approach, which consists in a novel extended DIC technique applied to a single set of IR images. It gives access to both displacement and temperature fields decomposed over the same discretization. This technique, applied to tensile tests on a NiTi SMA, reveals both strain localization due to the phase transformation and associated thermal dissipation.

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International audienceShape Memory Alloys (SMAs) undergo an austenite-martensite solid-solid phase transformation which confers its pseudo-elastic and shape memory behaviours. Phase transformation can be induced either by stress or temperature changes. That indicates a strong thermo-mechanical coupling. Tensile test is one of the most popular mechanical test, allowing an easy observation of this coupling: transformation bands appear and enlarge giving rise to a large amount of heat and strain localisation. We demonstrate that the number of transformation bands is strongly associated with the strain rate. Recent progress in full field measurement techniques have provided accurate observations and consequently a better understanding of strain and heat generation and diffusion in SMAs. These experiments bring us to suggest the creation of a new one-dimensional thermomechanical modelling of the pseudo-elastic behaviour. It is used to simulate the heat rise, strain localisation and thermal evolution of the NiTi SMA sample submitted to tensile loading

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Abstract. Many materials are concerned by strain localization, for instance PLC phenomena, Lüders' bands or Shape Memory Alloys (SMA). The experimental identification of such material behaviors requires the use of full field kinematic measurements, such as provided by Digital Image Correlation (DIC), as well as Infra-Red (IR) thermography to evaluate the associate thermal dissipation. Jointly, these field measurements allow for a full thermo-mechanical characterization of material behavior. However, the space and time association of both fields remains a major difficulty (antagonist surface texture requirements, imaging devices having different pixel number and acquisition rate...). In this paper, we introduce a much simpler experimental approach, which consists in a novel extended DIC technique applied to a single set of IR images. It gives access to both displacement and temperature fields decomposed over the same discretization. This technique, applied to tensile tests on a NiTi SMA, reveals both strain localization due to the phase transformation and associated thermal dissipation.

WOSInternational audienceThe specific behaviour of shape memory alloys (SMA) is due to a martensitic transformation. This transformation consists mainly in a shear without volume change and is activated either by stress or temperature. The superelastic behaviour and the one-way shape memory effect are both due to the partition between austenite and martensite. The superelastic effect is obtained for fully austenitic SMA: loaded up to 5% strain, a sample recovers its initial shape after unloading with a hysteretic loop. The oneway shape memory effect is obtained when a martensitic SMA, plastically deformed, recovers its initial shape by simple heating. Superelasticity and one-way shape memory effect are useful for several three-dimensional applications. Despite all these phenomena are well known and modelled in 1D, the 3D behaviour, and especially the one-way shape memory effect, remains quite unexplored. Actually, the development of complex 3D applications requires time-consuming iterations and expensive prototypes. Predictive phenomenological models are consequently crucial objectives for the design and dimensioning of SMA structures. Therefore, a series of 2D proportional and non-proportional, isothermal and non-isothermal tests have been performed. This database will be used to build a phenomenological model within the framework of irreversible processes

The paper presents a new multiscale modeling dedicated to magnetic shape memory alloys. It involves four scales from the domain scale to the macroscale. The model is presented and simulation results are compared to experiments carried out on a NiMnGa single crystal.

This paper presents a comparative study between two micro-macro modeling approaches to simulate stress-induced martensitic transformation in shape memory alloys (SMA). One model is a crystal plasticity based model and the other describes the evolution of the microstructure with a Boltzmann-type statistical approach.Both models consider a self-consistent scheme to perform the scale transition from the local thermomechanical behavior to the global one. The way the two modeling approaches describe the local behavior is analyzed.Similarities and differences are pointed out. Numerical simulations of the thermo-mechanical behavior of an isotropic titanium-niobium SMA are performed. These alloys have known a growing interest of scientific community given their high potential for application in the biomedical field. Stress-strain curves obtained from the two simulations are compared with experimental results. Evolutions of volume fractions of martensite variants predicted by the two approaches are compared for <100>, <110> and <111> tensile directions. Due to the absence of comparative studies between multiscale models dedicated for SMA, this paper fills a gap in the state of the art in this field and provides a significant step toward the definition of an efficient numerical tool for the analysis of SMA behavior under multiaxial loadings.KEYWORDS SHAPE MEMORY ALLOYS (SMA). MARTENSITIC TRANSFORMATION. MICRO -MACRO MODELING.