Physical properties (thermal,thermomechanical, magnetic,and adhesive) of some smart orthodontic wires

Thermal, thermomechanical, and caloric properties of commercial orthodontic wires (produced by Natural Orthodontics Corp., USA) with cylindrical and rectangular geometry were studied. Depending on the applied forces, there were identified the range of elasticity, the elasticity–viscoelasticity coexistence domain and the domain in which a maximum force of 18 N is applied, for the orthodontic wires. When increasing the thickness of orthodontic wires, deformation decreases. The Controlled Force Module, in the tension mode, was used for the determination of the orthodontic wires elongation at application of the stretching forces from 0 to 13 N, at 35 °C, maintaining each static force value for 3 min. The increase in the cross-sectional area of the orthodontic wires disfavors the process of elongation of the sample, at the same applied static force. Using the Multi-Frequency–Strain–Stress modulus, in the tension mode, DMA cyclic heating–cooling measurements were performed. The measured physical quantities for orthodontic wires were Storage Modulus, Loss Modulus, Tanδ and Stiffness, at heating and cooling. Thus, the characteristic temperatures of the phase transitions (A_s, A_f, M_s, M_f), of all the studied orthodontic wires were identified. Also, the values of the elasticity modulus (Young’s Modulus) of the orthodontic wires were calculated at 35 °C. With the DSC Q200 device, using temperature-modulated differential scanning calorimetry method, a multi-step temperature variation program, was applied to a rectangular wire, in three stages (cooling–heating–cooling). Through the interpretation of heat fluxes (reversible, irreversible and total), the phase transitions in the formation of martensite, austenite, but also of the rombohedral phase (R-phase), were identified. Formations of austenite and martensite were also evidenced by the classical DSC method, but the classical DSC method also enabled the R-phase identification. The adherence of some food dyes on the orthodontic wires, as well as the modification of the surface roughness of the orthodontic wire after the deposition of the food dye, was also studied. By magnetic measurements, it was established that the orthodontic wires had paramagnetic properties at room temperature, and nitinol was a mixture of 49.2% austenite and 50.8% martensite.

     

Witten Spinors on Nonspin Manifolds

Motivated by Witten’s spinor proof of the positive mass theorem, we analyze asymptotically constant harmonic spinors on complete asymptotically flat nonspin manifolds with nonnegative scalar curvature.     

Thermal study of a shape memory alloy (SMA) spring actuator designed to insure the motion of a barrier structure

The study concerns an experimental model using a SMA spring actuator for improving the whole performance of a barrier structure. The study is, specifically, focused on the thermal analysis of the SMA spring material and on determination of the SMA spring working time periods at different values of the activating electric current inducing different phase changing speeds.     

Hybrid Inorganic-Organic Sol–Gel Coatings in the SiO2-TiO2 System

In the present work, the influence of substituted Si-alkoxides on the structural and optical properties of films obtained in the SiO₂-TiO₂ system was studied. Methyltriethoxysilane (MTEOS) and 3-(tri-methoxysilyl)propyl methacrylate (TSPM) were used as SiO₂ sources and Ti(OBu)₄ was used as TiO₂ source. Acetylacetone was added to the Ti(OBu)₄ as chelating agent and the synthesis was carried out in acid medium. The films were deposited on oxidized Si-wafers by spin-coating. The films were characterized by XRD, spectro-ellipsometry (SE), and atomic force microscopy (AFM). The results obtained have shown that in the case of hybrid films the desired thickness could be obtained in a single deposition step. The thickness of the films and the optical properties are controlled by the bulkiness of the organic substitute bounded to Si. Among other optical applications, the potential use of such films as optical waveguides is proposed.     

Thermal characteristics of Ni–Ti SMA (shape memory alloy) actuators

For two typical actuators of intelligent systems (Ni–Ti SMA cantilever and SMA helical spring), the evaluation of their thermal characteristics is presented. In order to determine the transformation temperatures and other thermal parameters of the two studied elements, the attention was concentrated on thermal analysis experiments. For each actuator configuration, comprehensive graphical interfaces have been developed, to run in Visual Basic, with respect to the results of performed thermal analyses.     

Shape memory alloy-based smart module structure working under intense thermo-mechanical stress

The paper presents a complete model for a modular mechatronic structure actuated by a one-way memory effect shape memory alloy actuator. In order to claim the complete attribute of the model, the austenite transformation temperature evolution of actuator was evaluated in relation with the precision and repeatability related capabilities of the mechatronic structure. The evolution of austenite transformation temperature was obtained through determinations based on DSC method. Those determinations were performed on the shape memory alloy wire used as actuator in the modular mechatronic structure. The wire is subject of intense and repetitive operating mode. All determinations are performed on the SMA wire used as actuator system after 5,000, and 1,003,600 cycles, respectively. The results indicate a shift in both A _s and A _f temperatures, a trend that is heavily dependent on the operating history of the system. Using experimental results, authors built a graph (surface) that is based on heating time schedule, heating current, and austenite finish temperature. Also, the results lead to the conclusion that for any desired heating time, it can be identified (in a restricted but relatively wide range), at least a pair of both austenite finish temperature and heating current. If the control algorithm modifies the electrical current in accordance with the number of working cycles and austenite transformation temperature evolution, the time response and, by default, the structure repeatability are assured even after over 1 million working cycles.