Issue 29

V. Sepe et alii, Frattura ed Integrità Strutturale, 29 (2014) 85-96; DOI: 10.3221/IGF-ESIS.29.09 85 Focussed on: Computational Mechanics and Mechanics of Materials in Italy Response of porous SMA: a micromechanical study V. Sepe, S. Marfia University of Cassino and Southern Lazio v.sepe@unicas.it , marfia@unicas.it F. Auricchio University of Pavia auricchio@unipv.it A BSTRACT . Lately porous shape memory alloys (SMA) have attracted great interest as low weight materials characterized by high energy dissipation capability. In the present contribution a micromechanical study of porous SMA is proposed, introducing the simplifying hypothesis of periodic distribution of voids. The mechanical response of the heterogeneous porous medium is derived by performing nonlinear finite element micromechanical analyses considering a typical repetitive unit cell made of a circular hole in a dense SMA matrix and prescribing suitable periodicity and continuity conditions. The constitutive behavior and the dissipation energy capability of the porous Nitinol are examined for several porosity levels. Numerical applications are performed in order to test the ability of the proposed procedure to well capture the overall behavior and the key features of the special heterogeneous material. K EYWORDS . Shape Memory Alloys; Porous material; Micromechanics; Dissipation. I NTRODUCTION hape Memory Alloys (SMA) are characterized by a very special behavior due to their capability to undergo reversible changes of the crystallographic structure, depending on the temperature and on the stress state. These changes can be interpreted as reversible martensitic transformations between a crystallographic more-ordered parent phase, the austenite, and a crystallographic less-ordered product phase, the martensite. Thanks to their unique properties over the last decades SMA have been used for a large number of applications in several engineering fields, from aerospace to medical device industries. Recently, driven by biomedical applications, a great interest has arisen concerning a particular class of SMA: the porous SMA. Currently, several methods are adopted for manufacturing porous SMA from elemental powders. Many porous NiTi SMA with different structures of pores have been successfully produced by sintering at elevated pressure via a hot isostatic press or metal injection molding [1], spark plasma sintering [2], combustion synthesis with a self-propagating wave [3]. The possibility of producing SMA in porous form has opened new fields of applications owing to their low-weight with high energy dissipation properties. Porous shape memory alloys combine benefits from dense SMA and porous structure. In fact, even beyond the shape memory characteristics, porous SMA with a relatively low density can enlarge the applicability of dense SMA. In addition to the large recoverable strains observed by SMA, the porous counterpart offers S