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Prestress state evolution during thermal activation of memory effect in concrete beams strengthened with external SMA wires

Debska A., Gwozdziewicz Piotr, Seruga A., Balandraud X., Destrebecq J. F.

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 4

659--673

The memory effect of shape-memory alloys (SMAs) has opened interesting perspectives to create prestress states in concrete elements. However, the procedure has not been yet fully resolved due to the complex thermomechanical behavior of these alloys, in addition to the practical difficulties of mechanical coupling between SMA and concrete elements. The present study deals with tests on the development of prestressing forces in concrete beams during the thermal cycle required in the procedure. Pre-stretched nickel–titanium wires were externally placed on concrete prismatic beams equipped with strain gauges. As concrete rupture may occur during the heating by the Joule effect, a compromise must be found between the SMA pre-stretch level and the maximum temperature to be applied before returning to ambient temperature. A macroscopic model was developed to analyze this compromise. The complex thermomechanical response of SMAs implies a particular attention in the definition of the ambient temperature and heating conditions for the creation of prestress states in concrete components.

Comparative assessment of the corrosion process of orthodontic archwires made of stainless steel, titanium–molybdenum and nickel–titanium alloys

Małkiewicz K., Sztogryn M., Mikulewicz M., Wielgus A., Kamiński J., Wierzchoń T.

Archives of Civil and Mechanical Engineering

2018

Vol. 18, no. 3

941--947

The phenomenon of corrosion of orthodontic appliances is of interest to both clinicians and researchers dealing with the issue of biocompatibility of medical materials. The oral cavity, due to its temperature fluctuations, changing pH, high humidity, action of mechanical forces and the presence of microorganisms is a favorable environment for degradation of dental materials. This article presents the comparative assessment of the intensity of corrosion of orthodontic archwires made of alloy steel, nickel–titanium and titanium–molybdenum alloys in laboratory conditions. Corrosion resistance examinations were carried out by means of the impedance and the potentiodynamic methods using an Autolab PGSTAT100 potentiostat/galwanostat (Eco Chemie B.V., Holand) with FRA2 module, in non-deaerated artificial saliva solution at 37 °C. An analysis of the impendence method's data showing that the highest corrosion resistance is observed for NiTi arches (3M, USA), while the lowest resistance for SS arches (3M, USA). These observations were confirmed by the data obtained from potentiodynamic tests; it was observed that the average corrosion current density [Icor] was the lowest for nickel–titanium archwires (3M, USA) and averaged 2.50 × 10−3 μA/cm2. The highest Icor corrosion current was observed in the case of steel wires from the same manufacturer and averaged 4.96 × 10−2 μA/cm2.

Study on bioactivity of NiTinol after surface treatment

Chrzanowski A., Walke W., Armitage D., Knowles J.

Archives of Materials Science and Engineering

2008

Vol. 31, nr 1

5-8

Purpose: The aim of the work was to assess bioactive properties and corrosion resistance of nickel titanium alloy after alkali treatment and spark oxidation in Hank’s Balance Salt Solution. Design/methodology/approach: Surfaces of samples were prepared by chemical treatment in NaOH followed by heat treatment, and spark oxidation. Corrosion resistance was investigated using potentiodynamic method. Chemical composition of the samples surface was measured using SEM EDX. Surface roughness and topography was analyzed using AFM. Bioactive properties were analyses on the basis of the chemical composition of the samples immersed in HBSS for 14 days. Findings: The chemical composition analysis of the samples showed that alkali treatment increased significantly nickel content in top layer and also increase in roughness was observed. Spark oxidation results also in roughness increase. Corrosion test showed insignificant increase of the corrosion resistance after oxidation while alkali treatment caused drop of the resistance. Bioactivity study revealed that both applied treatments did not improve bioactive properties of the NiTinol when compared with simply ground samples. Research limitations/implications: Two types of the treatment applied for nickel titanium and intended to improve bioactive properties were investigated. There was no improvement in bioactivity observed after surface treatment. However, alternation in chemical composition, corrosion resistance, and topography were observed. Further analysis of biocompatibility and mechanical properties are required. Practical implications: Both chemical and electrochemical treatment, as presented in the paper, gave promising results in terms of wetting ability, topography and apatite film formation, however further study are required to confirm suitability of the treatments for medical applications. Originality/value: The obtained results revealed unsuitability of the alkali treatment intended to improve bioactivity of the Nitinol. Nevertheless, obtained results for spark oxidised samples were found promising in terms of the chemistry and topography and further biological studies are planned.