Abstract
The indentation response of a pseudoelastic nickel-titanium based shape memory alloy (SMA) has been analyzed. Indentation tests have been carried out at room temperature using a spherical diamond tip and indentation loads in the range 50-500 mN in order to promote a large stress-induced transformation zone in the indentation region and, consequently, to avoid local effects due to microstructural variations. The measured load-displacement data have been analyzed to obtain information on the pseudoelastic response of the alloy. To aid this analysis numerical simulations were performed, by using a commercial finite element (FE) softwarecode and a special constitutive model for SMAs, so as to understand better the microstructural evolution occurring during the indentation process. Finally, the FE model has been used to analyze the effects of temperature on the indentation response of the alloy. This analysis revealed a marked variation of both the maximum and residual penetration depths with increasing test temperature.
Highlights
N ickel-titanium (NiTi) based shape memory alloys (SMAs) have, over recent decades, attracted the interest of the scientific and engineering community due to their unique functional properties, namely the pseudoelastic effect (PE) and the shape memory effect (SME) [1], coupled with their good mechanical properties and biocompatibility
Despite the increasing interest and the efforts of many researchers to understand these unusual mechanisms, the use of NiTi alloys is currently limited to high-value applications, due to high raw material and manufacturing costs, the latter resulting from the need to control precisely the processing parameters since the functional and mechanical properties of NiTi alloys are significantly affected by the thermo-mechanical loading history experienced during manufacturing
As most NiTi components are characterized by complex shape and small size scale their properties cannot be directly obtained from the bulk raw material
Summary
N ickel-titanium (NiTi) based shape memory alloys (SMAs) have, over recent decades, attracted the interest of the scientific and engineering community due to their unique functional properties, namely the pseudoelastic effect (PE) and the shape memory effect (SME) [1], coupled with their good mechanical properties and biocompatibility. Well known contact mechanics theories for conventional metals cannot be directly applied to SMAs and work has been carried out, in recent years, to understand better the effects of microstructural transitions on the indentation response of both thin films [3,4,5,6,7,8] and bulk specimens [9,10,11,12,13,14,15]. The FE model has been used to analyze the effects of temperature and transformation stresses, calculated from the Clausius-Clapeyron relationship, on the indentation response of the alloy
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