1D Phenomenological Modeling of Shape Memory and Pseudoelasticity in NiTi Alloys

Abstract

A one-dimensional phenomenological approach to simulate both the mechanical and functional properties in shape memory alloys (SMAs) is described in the following sections. In fact, shape-memory alloys exhibit unique mechanical and functional features, due to reversible transformations in crystal structure. In particular, on the macroscopic scale, SMAs are able to remember a geometrical shape and can return to that shape by activating the phase transition mechanisms. Many kinds of SMAs have been exploited in the last decades, such as the copper-zinc-aluminum (ZnCuAl), copper-aluminum-nickel (CuAlNi), nickel-manganese-gallium (NiMnGa), nickel-titanium (NiTi), and other ones made by alloying zinc, copper, gold, iron, etc. Among these alloys the near equiatomic NiTi binary system shows the most exploitable characteristics due to the high stress and strain recovery capabilities associated with their functional properties, namely pseudoelastic effect (PE) and shape memory effect (SME). These properties are due to a reversible solid state phase transformation between a parent phase (austenite) and a product phase (martensite), the so called thermoelastic martensitic transformation (TMT), that can be activated either by temperature (Thermally Induced Martensite, TIM), or by applied stress (Stress Induced Martensite, SIM) [1]. Due to these features NiTi alloys are currently used in an increasing number of applications in many fields of engineering [2], for the realization of smart sensors and actuators, joining devices, hydraulic and pneumatic valves, release/separation systems, consumer applications and commercial gadgets. However, thanks to their good mechanical properties and biocompatibility the most important applications of NiTi alloys are in the field of medicine, where pseudoelasticity is mainly exploited for the realization of several components, such as cardiovascular stent, embolic protection filters, orthopedic components, orthodontic wires, micro surgical and endoscopic devices. As a direct consequence of their interesting features NiTi alloys have attracted the interest of scientific and engineering community in the last years. However, despite the increasing interest and the efforts of many researchers to better understand these unusual mechanisms, the use of NiTi alloys is currently ©2012 Maletta and Furgiuele, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1D Phenomenological Modeling of Shape Memory and Pseudoelasticity in NiTi AlloysCarmine Maletta and Franco Furgiuele Additional information is available at the end of the chapter http://dx.doi.org/10.5772/51283Chapter 5 2 Will-be-set-by-IN-TECH limited to high-value applications (i.e. medical devices, MEMS, etc.), due to the high cost of the raw material as well as to the complex component manufacturing; in fact, ...