PSI - Issue 33

V. Di Cocco et al. / Procedia Structural Integrity 33 (2021) 1035–1041 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. Comparison between experimental and model results applied at investigated cycles

4. Conclusions From the X-Ray diffraction analyses it possible to conclude that: 1) The austenite-martensite transition behavior is not linear, but it can be expressed by an equation used in the diffusion driving phenomena; 2) The austenite-martensite transition can be expressed by an equation used in the diffusion driving phenomena; 3) The histeresis is an effect present also in terms of austenite-martensite transition. Furthermore, an integrated structural-mechanical model was proposed to describe the cyclic behaviour of shape memory alloys with pseudo-elastic behaviour. The young modulus of the alloy is calculated as the "parallel of stiffnesses" associated with austenite and martensite, characterised by their respective young moduli weighted by their quantity and reduced by the amount of phase being transformed. Using two parameters difining the influence of transforming phases amount the model is able to describe also the hysteresis of the cycle. Natali S., Maletta C, Di Cocco V, Iacoviello F. Cyclic microstructural transitions and fracture micromechanisms in a near equiatomic NiTi alloy. Int J Fatigue 2014;58:136–43. doi:10.1016/j.ijfatigue.2013.03.009. Brotzu A., Iacoviello F, Di Cocco V, Natali S. Grain size and loading conditions influence on fatigue crack propagation in a Cu-Zn-Al shape memory alloy. Int J Fatigue 2018;115:27–34. doi:10.1016/j.ijfatigue.2018.06.039. Di Cocco V, Iacoviello F, Natali S, Volpe V. Fatigue crack behavior on a Cu-Zn-Al SMA. Frat Ed Integrita Strutt 2014;30:454–61. doi:10.3221/IGF-ESIS.30.55. Kuribayashi K, Tsuchiya K, You Z, Tomus D, Umemoto M, Ito T, et al. Self-deployable origami stent grafts as a biomedical application of Ni rich TiNi shape memory alloy foil. Mater Sci Eng A 2006;419:131–7. doi:https://doi.org/10.1016/j.msea.2005.12.016. Shimamoto A, Zhao HY, Abé H. Fatigue crack propagation and local crack-tip strain behavior in TiNi shape memory fiber reinforced composite. Int J Fatigue 2004;26:533–42. doi:https://doi.org/10.1016/j.ijfatigue.2003.09.005. Gollerthan S, Young ML, Baruj A, Frenzel J, Schmahl WW, Eggeler G. Fracture mechanics and microstructure in NiTi shape memory alloys. Acta Mater 2009;57:1015–25. doi:https://doi.org/10.1016/j.actamat.2008.10.055. Furgiuele F, Maletta C, Falvo A, Barbieri G, Brandizzi M. Fracture Behaviour of Nickel-Titanium Laser Welded Joints. J Mater Eng Perform 2009;18:569–74. doi:10.1007/s11665-009-9351-8. Gall K, Tyber J, Wilkesanders G, Robertson SW, Ritchie RO, Maier HJ. Effect of microstructure on the fatigue of hot-rolled and cold-drawn NiTi shape memory alloys. Mater Sci Eng A 2008;486:389–403. doi:https://doi.org/10.1016/j.msea.2007.11.033. Robertson SW, Ritchie RO. A fracture-mechanics-based approach to fracture control in biomedical devices manufactured from superelastic Nitinol tube. J Biomed Mater Res Part B Appl Biomater 2008;84B:26–33. doi:https://doi.org/10.1002/jbm.b.30840. Wang GZ, Xuan FZ, Tu ST, Wang ZD. Effects of triaxial stress on martensite transformation, stress–strain and failure behavior in front of crack tips in shape memory alloy NiTi. Mater Sci Eng A 2010;527:1529–36. doi:https://doi.org/10.1016/j.msea.2009.10.038. Baxevanis T, Lagoudas D. A mode I fracture analysis of a center-cracked infinite shape memory alloy plate under plane stress. Int J Fract 2012;175:151–66. doi:10.1007/s10704-012-9709-z. References