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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 4 2 form of 〈 111 〉 B2 Ni clusters as concluded from the observed diffuse intensity in the electron diffraction patterns revealing short-range ordering enhancement. Performing thermal cy- cling in some different temperature ranges to separate the ef- fect of martensitic transformation and high temperature range of differential scanning calorimetry cycling revealed that both high temperature- and martensitic transformation-included cycles enhance the short-range ordering (Fig. 2). FUNCTIONAL AND STRUCTURAL FATIGUE OF PSEUDOELASTIC NiTi: GLOBAL VS. LOCAL THERMO-MECHANICAL RESPONSE Franco Furgiuele, Pietro Magarò, Carmine Maletta, and Emanuele Sgambitterra Functional and structural fatigue properties of a pseu- doelastic NiTi alloy were analyzed at the light of local non- homogenous thermo-mechanical response, resulting from Lüder’s-like transformation bands. To this aim, in-situ full-field strain and temperature measurements were made during fa- tigue tests. Structural and functional fatigue damage phenom- ena were studied by analyzing the evolutions of strains and temperature at the sample scale as well as within the transfor- mation bands. Marked losses in the pseudoelastic recovery ca- pabilities were recorded, mainly occurring in the first loading cycles, leading to material stabilization after about 200 cycles. Very large differences between the two scales were observed, that is, reduction of pseudoelastic recovery at the global scale is attributed to the accumulation of residual deformation in the transformation bands. These local effects tend to vanish for strains beyond the stress-induced transformation regime, due to the saturation of martensitic bands. The effects of lo- cal deformations on the structural fatigue properties, in terms of strain-life curves, were also analyzed. It was demonstrated that localized strains play a very important role on the evolu- tion of structural damage, especially within the pseudoelastic regime of the alloy, and they represent the key to understand unusual strain-life curves at the global scale (Fig. 3). ON THE IMPORTANCE OF STRUCTURAL AND FUNCTIONAL FATIGUE IN SHAPE MEMORY TECHNOLOGY Jan Frenzel This article provides a brief overview on structural and functional fatigue in shape memory alloys (SMAs). Both de- generative processes are of utmost technological importance because they limit service lives of shapememory components. While our fundamental understanding of these two phenom- ena has improved during the last two decades, there are still fields which require scientific attention. NiTi SMAs are prone to the formation of small cracks, which nucleate and grow in the early stages of structural fatigue. It is important to find out how thesemicro-cracks evolve into engineeringmacro-cracks, which can be accounted for by conventional crack growth laws. The present work provides examples for the complexity of short crack growth in pseudoelastic SMAs. The importance of functional fatigue has also been highlighted. Functional fa- tigue is related to the degeneration of specific functional char- acteristics, such as actuator stroke, recoverable strain, plateau stresses, hysteresis width, or transformation temperatures. It is caused by the accumulation of transformation-induced de- fects in themicrostructure. The functional stability of SMAs can be improved by (1) making phase transformations processes smoother and (2) by improving the material’s resistance to ir- reversible processes like dislocation plasticity. Areas in need of further research are discussed (Fig. 4 on next page). SMJ HIGHLIGHTS Fig. 3 — Cyclic evolution of the stress–strain response at the global scale: (a) stabilized hysteresis cycles at different maximum strain and cyclic curves; (b) variation of the peak and transformation stresses after material stabilization with respect to the first cycles. 1 2