Papers by Keyword: Shape Memory

Abstract: The research of deposition of a nitinol sample in an equiatomic ratio from a powder mixture of nickel and titanium 55Ni-45Ti (in wt.%) is aimed at studying the heterogenicity of the chemical composition in the cross-section of a thin-walled and multilayer (bulk) cylindrical sample. The main task of the study was to determine the presence or absence of the chemical composition deviation from layer to layer, and mechanical properties. Analysis on an optical microscope, EDS analysis, and microhardness measurement, a thin-walled sample was studied. A chemical gradient was detected in the sample from the base along with its entire height. An increase in the content of the Ti element and a decrease of the Ni element was detected with an increase in the number of layers and the height of the sample, and a change in the microstructure and hardness were found. The increase in hardness from the base to the top point of the sample reaches 50%. X-ray phase analysis (XRD) showed the presence of NiTi phases in the martensitic and austenitic state, the side phases of NiTi2 in a thin-walled sample, and the presence of the Ni4Ti3 phase and the TiO2 oxide phase in a cylindrical bulk sample. The chemical composition of the cylindrical bulk sample agrees with the chemical composition of the mixture loaded into the powder feeder 55:45 Ni and Ti in wt. %. To indirectly determine the shape memory effect of the final alloy, mechanical tests were carried out for compression of cylindrical samples with subsequent heating, which confirmed the presence of the shape memory effect with a degree of reversible deformation of about 40%.

Abstract: The method of synthesis of new polyurethane urea thermoplastic elastomers with controlled physical network density by varying the crystallization rate of the soft block and the structure of the interphase has been developed. Fine-tuning of morphology and mechanical properties allows to desighn adaptive materials with shape memory. By combination of calorimetric and X-ray diffraction methods, the influence of chemical nature of diaisocyanates and the ratio of two types of crystallizable blocks, polybutylene glycol adipate diol (PBA) and poly-ε-caprolactone diol (PCL), on the structure and termal behavior of the thermoplastic elastomers has been studied.

Abstract: Synthesis of Cu-Ni-Al alloy has been realized by powder metallurgy. Mechanical alloying was used to produce shape memory alloy consisting of Cu, x Al, and 5wt, % Ni to study the effect of using the aluminum ratios of 12.5, 13, and 13.5 wt.% and sintering temperature on the transformation temperature. The process to obtain the alloy has included cold compaction at 600 MPa, Ar Gas sintering at 950 °C, die forging at 900 °C under the pressure of 500 MPa, and heat treatment at 850 °C followed by water quenching. The results have shown that the proposed synthesis route could be used to obtain the alloy with proper transformation and metallurgical properties.

Abstract: The aim of this work is indentation study of local mechanical properties of Cu-22Zn-4.6Al alloy, which has significant shape memory effect after quenching from dual α + β phase region. The study was carried out on the samples with thermoelastic and non-thermoelastic martensite in the structure, which were obtained by quenching from various temperatures. A different behavior concerning mechanical properties measurements of α phase and β phase transformed to martensite after quenching from various temperatures was found out. It was observed almost no change of mechanical properties of α phase, whereas indentation hardness H_IT and indentation modulus E_IT raised with increasing quenching temperature. Also some serious differences were observed at indentation test of thermoelastic and non-thermoelastic martensite.

Abstract: The skin of buildings represents the first level of communication between construction, man and environment. In this relationship, the concept of communication acquires different values, because it can be applied both to the architectural field in relation to the shape, and to the perceptive and communicative sphere, aimed to transmission of messages or even to the interaction of the architectural envelope with the user and the environment. This brings us back to the energy and sustainability aspects, since the primary role as a separation and filter layer of the building façades is that of shielding. The solution with a kinetic façade constitutes not only a possibility of climatic mediation between outside and inside, guaranteeing ventilation and protection from solar radiation, but allows to redesign the aesthetic, communicative and perceptive appearance of a building. The contribution focuses on the communicative and perceptive potential of the façades and the ongoing experimentations of the new smart materials applied to these.

Abstract: NiTi alloy is usually prepared by casting and forming. As an innovative process, reactive sintering powder metallurgy is tested worldwide, aiming to prepare pure NiTi alloy easily from nickel and titanium powders. This process enables to prepare both porous and low-porosity alloy, depnding on the process conditions. However, the formation of NiTi phase in this process is always accompanied by the Ti₂Ni phase, which is hard, brittle, less corrosion resistant and does not have the shape memory. In this work, various alloying elements (Al, Si, Mg, Fe, Nb, V) were added to Ni-Ti alloy in order to lower the amount of Ti₂Ni phase or at least to minimize its undesirable effect on the alloy properties. The reactive sintering behaviour, phase composition and mechanical properties of Ni-Ti-X alloys were described.

Abstract: Recently, Ni-free shape memory Ti-based alloys (composed of the biocompatible β-stabilizing elements such as Ta and Nb) are extensively studied. In this work, new Ni-free Ti-17Nb-6Ta is presented as a candidate for shape memory alloys with high biocompatibility. This alloy produced using arc-melting in argon atmosphere, followed by solution annealing at 900° C for 30 min. β-phase is the predominant phase beside α” martensite phase. Stress induced martensitic transformation is observed after cold rolling and during bending tests as measured by XRD. The hardness of the bended wire in the solution treated condition was around 330HV. While the cold rolled wire hardness before bending was 300 HV. The superelasticity and shape memory effect was investigated through bending tests of alloy wires. The cold rolled wire showed higher superelasticity than shape memory effect. But superelasticity and the shape memory effect were almost similar with the solution treated wire. Also, the total spring back in cold rolled wire is higher compared with solution treated wire.

Abstract: This study aims to address the amount of force delivered by a fabricated NiTiCu orthodontic wire with a ternary composition ratio of 46.0 Ni: 49.0 Ti: 5.0 Cu and to compare the results with a commercial NiTiCu35^oC orthodontic archwire. Nickel (purity 99.9%), Titanium (purity 99.8%), and Copper (purity 99.9%) were used in this study with the atomic weight ratio 46.0 Ni: 49.0 Ti: 5.0 Cu. The elements were melted to form an alloy using an electrolytic arc furnace in argon gas atmosphere and homogenized at 800^oC for 1 hr. The alloys were subsequently sliced into thin plates (1.5mm) by EDM wire cutting machine to obtain the specimens and were cold-rolled with 30% reduction followed by heat treatment in a furnace at 400^oC for 1 hour. Then, the three newly fabricated NiTiCu specimens were cut in nearly identical wire sizes of 0.016 inch x0.022 inch. Commercial preformed Ormco NiTiCu35^oC archwire with size 0.016 inch x 0.022 inches were used for comparative purposes. Three-point bending test was performed using a Universal Testing Machine to investigate the force of the load-deflection curve at oral temperature (36^oC+ 1) with deflection points at 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5 mm. Descriptive statistics was used to evaluate each variable and independent t-test was used to analyze the differences between the groups. It was found that both NiTiCu wires presented typical superelastic properties as observed from the load-deflection curve. The average force was 341.70 g for loading, and 264.18 g for unloading for 46.0 Ni: 49.0 Ti: 5.0 Cu wire. Similarly, the values were 299.88 g for loading, and 201.96 g for unloading for Ormco NiTiCu35^oC. There were significant differences (p<0.05) in mean loading and unloading forces between the two NiTiCu wires. The deflection forces in loading and unloading force for Ormco NiTiCu at each point were less than 46.0 Ni: 49.0 Ti: 5.0 Cu wire, except at the deflection point of 0.25 mm. Regarding the force difference between each deflection point of loading and unloading force, Ormco NiTiCu35^oC exerted less force than 46.0 Ni: 49.0 Ti: 5.0 Cu wire, except at difference deflection at 1.5-1.25 mm of unloading force. However, there were still within the acceptable limits for orthodontic use. It is concluded that the fabricated ternary alloy of 46.0 Ni: 49.0 Ti: 5.0 Cu (atomic weight) with 30% reduction and heat treatment at 400^oC for 1 hr. and Ormco 35^oC NiTiCu presented the characteristics of both superelastic and shape memory in their wire form. The unloading forces of both NiTiCu wires were in the range of orthodontic use. This should be a good foundation for further studies towards development of new orthodontic NiTiCu archwires.

Abstract: Aircraft morphing with regard to UAVs has recently gained incredible momentum; however, only a limited amount of research has been conducted on its effect on tailless aircraft. This is partly due to aerodynamic compromises such as directional instabilities that arise in the absence of a vertical stabilizer. Yet birds readily adapt to adverse flight conditions without vertical stabilizers and are unhindered with respect to stability and maneuvering due to their smooth continuous shape change and rapid muscle response. This research, motivated by the discrepancy between manmade and natural flight designs, investigates the aerodynamic effects of a smart morphing horizontal tail exhibiting bending-twisting coupling for yaw control on a bio-inspired aircraft. The structural response due to actuation was determined using Abaqus and coupled with a Reynolds-averaged-Navier-Stokes turbulence model for a low-Reynolds-number fluid analysis of the deformed shape. The morphing tail was simulated as piezoelectric Macro Fiber Composites with oriented PZT rods. Directional moment and stability derivative are presented to gain insight into the effect of the morphing horizontal tail on yaw control.

Abstract: Ionic polyurethane (IPU) was synthesized as shape memory materials. Poly (tetramethylene ether) glycol with 2000g/mol number average molecular weight were used as soft segment, 4,4-methylenebis (phenyl isocyanate), and 1,2-dihydroxy-3-propanesulfonic acid salt were used to compose the segment of SMP materials. The structure and properties of these IPU films were characterized by Fourier Transform infrared, X-ray diffraction, Thermal gravimetric analysis and Differential scanning calorimeter. The results showed that the glass transition temperature of the IPU increased with the increase of hard segment content. The physical properties in terms of swelling property, water absorption and ion-exchange capacity increased with the improving of sulfonic group content in IPU. The shape memory property of IPU exhibited that the shape fixity ratio and recovery rate improved remarkably with the increase of hard segment content.