Memory Effect Properties Research Articles

Comparison of Loading and Unloading Behavior of Commercial and Locally Made Copper-Nickle-Titanium (NiTiCu) Orthodontic Archwire

Background: Copper-nickel-titanium (NiTiCu) archwire has been favoured in clinical orthodontic practice because of its superior superelasticity (SE) and shape memory effect (SME) properties. Objective: To compare the loading and unloading behavior of commercial NiTiCu orthodontic archwire and locally made NiTiCu orthodontic archwire based on composition and mechanical properties especially in relation to percentage recovery, stress plateau, stress hysteresis, and loading and unloading slope. Materials and Methods: The materials used were divided into two categories: the NiTiCu (40°C) commercial Ormco brand (USA) archwires and the locally made NiTiCu archwires produced at King Mongkut University of Technology Thonburi (KMUTT). The samples were examined using an Electron Probe Microanalysis (EPMA) to test their chemical composition. For loading and unloading behavior the Universal Testing Machine (Instron) was used for the three-point bending test. The Mann-Whitney U test was employed to analyze and compare the data. Results: Chemical composition, there were significant differences in at.% of Ni, Ti, and Cr composition between commercial and locally made archwire. There was no significant difference in at.% in Cu. In terms of percentage recovery, there was a significant decrease in locally made archwire. For stress plateau and stress hysteresis, there were also significant increases in Thai-made archwire when compared with commercial archwires. In addition NiTiCu (Ormco) showed significantly less inclination than locally made NiTiCu archwire in both loading and unloading slopes. Conclusion: Based on the results of this study, the mechanical properties of the locally made archwires were not as suitable as the commercial archwires. This preliminary study provides useful information for the further development of locally made NiTiCu archwires. Therefore, the use of the NiTiCu should be considered on a case by case basis. This experiment was useful in comparing locally made NiTiCu wire and commercial orthodontic wire.

Behaviour of NiTi SMA Helical Springs under Different Temperatures and Deflections

Shape memory alloys (SMAs) are one of the most widely used smart materials in many applications because of their shape memory effect property. In this work, the behaviour of NiTi SMA helical spring was evaluated through isothermal force-displacement experiment (IFDE) and shape recovery force experiment (SRFE). The transformation temperatures of SMA spring were determined by differential scanning calorimetry (DSC) test. In situ heating of SMA spring by direct electric current was used instead of conventional furnace heating. The continuous measurement of temperature of SMA spring during heating and cooling was ensured with attaching the thermocouple by heat shrinkable sleeve. From IFDE, the force-deflection behaviour under different constant temperatures and from SRFE and the force-temperature behaviour under different constant deflections are obtained. The results of IFDE show that the force increases and the residual displacement decreases with an increase in the temperature, and the stiffness of the spring at austenite state is greater than that at martensitic state. The results of SRFE show that the shape recovery force increases more or less linearly with an increase in the initial deflection for the same temperature range. But the shape recovery forces are not similar during heating and cooling stages. This paper presents the experimental setup, experimental procedures, and the observed behaviour of SMA helical springs under different temperatures and deflections.

The influence of the Ti4+ location on the formation of self-assembled nanocomposite systems based on TiO2 and Mg/Al-LDHs with photocatalytic properties

Herein, we report the formation of TiO2/LDH self-assembled nanocomposite systems using the memory effect property of the layered clay-type materials. Two different synthesis approaches, based on the modification of the initial brucite-like sheets composition, were used in order to investigate the influence of the Ti4+ location on the quality of the final products: the reconstruction of a calcined MgAl-LDH in a TiOSO4·xH2O aqueous solution and the reconstruction of a calcined MgAlTi-LDH in aqueous solution. The reconstruction process, monitored using X-ray diffraction, IR spectroscopy, UV–vis diffuse reflectance spectroscopy, SEM and thermal analysis, produced different structural changes strongly related with the brucite-like sheets composition. The photocatalytic activity of the obtained nanocomposite systems was evaluated for the degradation of the methyl-orange (MO) dye. An intimate contact has been created between the anatase and the brucite-like sheets in the nanocomposite systems, which had a direct influence on the HO radical production enhancing thus the photocatalytic performances. When comparing the as-synthesized catalysts, the MgAlTi-LDH solid manifests very powerful photocatalytic effect due to the segregation of small, well defined TiO2 nanoparticles on the highly hydroxilated layered surface. Up to 93% of the dye could be removed by a TiO2/LDH-type nanocomposite system. Controlled thermal treatment of photocatalytic systems allowed us to tailor the quality of the photocatalytic active sites deposited on the layered support. The use of the TiO2/LDHs nanocomposites showed multiple advantages highlighted by the increased activity per mass, higher efficiencies at a decreased solid/liquid ratio, decreased reaction times, reduced agglomeration and easy to separate at the end of the processes.

An overview of intermetallics research and application: Status of thermal spray coatings

The aim of this review is to update and to offer an overview of the investigations that have more recently been made on intermetallics, to highlight their importance for several applications in many areas and to examine topics for future research. The main subject is the application of intermetallics as thermal spray coatings. This will allow balancing the discussion of whether they are promising as a surface medium for materials that work at high temperatures. The general intermetallics classification includes iron, nickel, and titanium aluminides, as well as transition metal silicides. As nickel aluminides have been important in issues related to bonding coats, their research trajectory has been revised. Moreover, as the Fe-Al system has also been studied in terms of thermal spray processing, its good characteristics have also been assessed. The third intermetallic this article focuses on is NiTi, which appears not to be included in general classifications of intermetallic compounds, but it deserves to be mentioned mainly due to its shape memory effect and biocompatibility properties.

Freely movable ferromagnetic shape memory nanostructures for actuation

This paper presents the design and fabrication of freely movable ferromagnetic shape memory nanostructures for actuation in nanometer dimensions. Ni-Mn-Ga is chosen as a transducer material as it combines the shape memory effect and ferromagnetic properties. In order to avoid process incompatibilities due to heat treatment at high temperatures, a new nanomachining process is developed based on low temperature sputter deposition of epitaxial Ni-Mn-Ga films, electron beam lithography (EBL), ion beam etching (IBE) and a Cr based sacrificial layer technology. In situ bending experiments in a scanning electron microscope (SEM) reveal a stiffness coefficient in the martensite phase in the order of 1.5x10^1^1N/m^2.

Shape memory effect and thermomechanical properties of shape memory polymer fabric composite in tension mode

Fibers and fabrics are often used to reinforce shape memory polymers (SMPs) to improve their mechanical strength and properties, and the composites have been widely used in engineering. However incorporation of fibers and fabrics in SMPs are often accompanied with the degradation of thermal mechanical properties and shape memory effect. The thermomechanical properties and degradation mechanisms of a shape-memory polymer composite (SMPC) were investigated. Up to 100% extension, the SMPCs showed good shape memory effect with excellent recovery ratio, recovery stress and mechanical properties; while beyond that the recovery ratio and stress of the composites deteriorate rapidly due to the significant delamination and debonding of fibers and fabrics from the SMP resin and accumulation of broken fibers.

Seismic control of concrete shear wall using shape memory alloys

Shape memory alloy is a new functional material, which has found increasing applications in many engineering areas. Research efforts have been extended to use shape memory alloy in controlling civil structures. In this article, both pseudoelastic and shape memory effect properties of Nitinol shape memory alloy are implemented for control of concrete shear wall structure when subjected to seismic excitation. First, the behavior of the concrete shear walls equipped with shape memory reinforcements in its pseudoelastic characteristics is assessed, and the results are compared with the behavior of the ordinary concrete shear wall utilizing steel reinforcements. A finite element time history analysis is employed, and the results indicate that the proposed enhancement of the concrete shear wall with shape memory alloy reinforcements is able to reduce the permanent residual strain in the structure and hence attain reasonable improvement in seismic response. Then, the memory effect characteristics of shape memory alloys by imposing pretension in SMA rebar in concrete shear wall are evaluated. The results show that the concrete shear wall equipped with pretension rebars is much stiffer than either the concrete shear wall equipped with pseudoelastic shape memory alloy rebars or the ordinary concrete shear wall with steel.

Unique Multifunctional Thermally-Induced Shape Memory Poly(p-dioxanone)–Poly(tetramethylene oxide)glycol Multiblock Copolymers Based on the Synergistic Effect of Two Segments

Biodegradable and biocompatible poly(p-dioxanone)–poly(tetramethylene oxide)glycol (PPDO–PTMEG) multiblock copolymers with excellent shape memory effect and mechanical properties were developed by coupling PPDO-diol and PTMEG-diol with 1,6-hexamethylene diisocyanate (HDI). The influences of chain structure, microphase separating morphology on shape memory effect, and biocompatibility were investigated systematically. The TEM observation of PPDO–PTMEG poly(ether-ester)-polyether exhibited the relationship between characteristic microphase separating morphology and shape memory effect. Interestingly, differential scanning calorimetry (DSC) analysis indicated that Tg,PPDO was close to Tc,PTMEG, which provided the possibility that the reversible phase combined PTMEG segments and the amorphous phase of PPDO segments. The synergistic effect ensured copolymers owning both high Rf and Rr (96.6% and 92.9% with PTMEG segments only 15% in weight fraction), as well as the mechanical properties when T > Ttrans. Moreov...

Research on the shape memory effect and thermalelasticity of a novel intellectual damping material

In this paper, we introduce a novel intellectual damping materialshape memory alloy metal rubber (SMAMR), which is made from the shape memory alloy through the process similar to that for metal rubber. The shape craft, shape memory effect and mechanical properties are tested and discussed. The results show that the SMAMR has the combination properties of both shape memory alloy and metal rubber, such as high elasticity and damping capacity, low density, designable porosity, shape memory effect, and temperature dependent mechanical properties. The SMAMR not only has modulus and loss factor varying linearly with temperature during the phase transformation between Martensite and Austenite, which is quite available in the active control of vibration; but also has the modulus and loss factor large enough to be used as bearing structure. So the SMAMR is a significant integration of both functional material and structural material, and is quite attractive in active vibration control.

A shape memory alloy based tool clamping device

The traditional collet-chuck mechanism for tool clamping is a significant source of errors in spindles due to stack-up tolerances. This, in turn, adversely affects the tool's error motions particularly in demanding micro-cutting operations performed with ultra-high-speed miniaturized spindles. Hence, novel thought for miniature tool clamping is needed to minimize tool run-out and error motions in order to meet the necessary cutting speeds and accuracy requirements. In this paper a couple of Shape Memory Alloy (SMA) based solutions for the clamping of miniature tools will be explored. For clamp actuation the so-called Two-Way Shape Memory Effect (TWSME) property of NiTi SMAs will be exploited. The basic principles, design requirements, analysis and physical realization of these devices will be discussed. It will be shown through experimental verification tests that clamping forces in excess of tens of Newtons are possible, confirming thus the feasibility of the proposed solutions.

Effect of tellurium on machinability and mechanical property of CuAlMnZn shape memory alloy

Abstract The microstructure transition, shape memory effect, machinability and mechanical property of the CuAlMnZn alloy with and without Te have been studied using X-ray diffraction analysis, chips observation and scanning electron microscopy (SEM), tensile strength test and differential scanning calorimeter (DSC), and semi-quantitative shape memory effect (SME) test. The particles with richer Te dispersedly distributed in grain interior and boundary with size of 2–5 μm. After the addition of Te, the CuAlMnZnTe alloy machinability has been effectively increased to approach that of BZn15–24–1.5 and its shape memory property remains the same as the one of CuAlMnZn alloy. The CuAlMnZn shape memory alloys with and without Te both have good ductility as annealed at 700 °C for 15 min.

Metamagnetic Shape Memory Effect and Magnetic Properties of Ni-Mn Based Heusler Alloys

In some Ni-Mn-In- and Ni-Mn-Sn-based Heusler-type alloys, martensitic transformation from the ferromagnetic parent phase to the paramagnetic martensite phase appears and magnetic field-induced reverse transformation, namely, metamagnetic phase transition, is detected. In this paper, the metamagnetic shape memory effect due to the metamagnetic phase transition and the magnetostress effect in the Ni-Co-Mn-In alloys are introduced and the phase diagrams of Ni50Mn50-yXy (X: In, Sn, Sb) alloys are shown as basic information. Furthermore, the magnetic properties of both the parent and martensite phases in the Ni-Mn-In- and Ni-Mn-Sn-based metamagnetic shape memory alloys are also reviewed.

Covalent Bonding of Surface-modified Montmorillonite Nanoparticle with Polyurethane and its Impact on Shape Memory Effect and Mechanical Properties

The surface-modified nanoparticle, monmorillonite (MMT), was chemically bonded to shape memory polyurethane (SMPU) to improve shape memory and mechanical properties compared to the conventional composite prepared by melt-mixing process. Cloisite 30B was selected as MMT, because the functional group on its surface, methyl tallow bis-2-hydroxyethyl ammonium group, could be used for chemical bonding with SMPU and the reduced surface hydrophilicity rendered MMT disperse better in SMPU matrix during chemical reaction compared to bare MMT. Two types of SMPU, differing according to their soft segment (PTMG) and MMT content, were compared in mechanical and shape memory properties. Maximum stress went up as high as 57 MPa, and strain remained above 1000% for all of SMPUs. Shape recovery improved up to 97%, and did not decrease after four repetitive cyclic tests. Here, results demonstrating the advantages of chemical bonding of MMT-linked SMPU, compared to MMT and PU composite made by melt-mixing method, are discussed.

COMPARATIVE STUDY OF CLINICALLY USED NiTi ORTHODONTIC WIRES

The purpose of the study was to comparatively investigate two NiTi orthodontic wires. It is valuable to determine the phase transformation temperature and corrosion characteristics of the orthodontic wires to further study the shape memory effect and corrosion resistance properties. Optical microscope and EDX analysis were used for microstructure characteristics and composition analysis. Differential scanning calorimetry (DSC) was carried out to identify the phase transformation behavior of the two wires. Electrochemical tests in artificial saliva at 37 ±1°C including polarization and electrochemical impedance spectroscopy (EIS) were used to assess the corrosion resistance and corrosion mechanism of the wires. It was found that the transformation temperature range of A-wire (imported) is narrower while the As and Af are close to the body temperature, which is more suitable in the orthodontic operation at early stage. The corrosion current density of A-wire is lower than that of B-wire (domestically made) while the corrosion potential is higher. EIS test results indicated that the corrosion mechanism was the same. However, the oxide layer formed on the surface of A-wire is more protective.

Microstructure, martensitic transformation and superelasticity of Ti 49.6Ni 45.1Cu 5Cr 0.3 shape memory alloy

The aim of this study is to investigate the microstructure, martensitic transformation behavior, shape memory effect and superelastic property of Ti 49.6Ni 45.1Cu 5Cr 0.3 alloy, with Cu and Cr substituting for Ni. After annealing, the alloy showed single step A–M/M–A transformations within the whole annealing temperature range of 623 K to 1273 K even in the presence and Ti 2(Ni, Cu) precipitates. With the increase of the annealing temperature, the transformation temperatures exhibited three stages: increasing from 623 K to 873 K, decreasing from 873 K to 1023 K and unchanging from 1023 K to 1273 K. Meanwhile, the critical stress for stress induced martensitic (SIM) transformation decreased to a minimum value and increased after that, exhibiting a V shape curve. The alloy annealed at 623, 773 and 923 K exhibited shape recovery ratio more than 90% when the deformation strain was below 20%.

Recovery and residual stress of SMA wires and applications for concrete structures

In general, NiTi shape memory alloys are used for applications in civil structures. NiTiSMAs show good superelasticity and shape memory effect properties. However, forapplication of the shape memory effect, it is desirable for SMAs to show a widetemperature hysteresis, especially for civil structures which are exposed to severeenvironmental conditions. NiTiNb SMAs, in general, show a wider temperature hysteresisthan NiTi SMAs and are more applicable for civil structures. This study examines thetemperature hysteresis of NiTiNb and NiTi SMAs, and their recovery and residual stressare investigated. In addition, the tensile behaviors of SMA wires under residual stress areevaluated. This study explains the possible applications for concrete structureswith the shape memory effect and illustrates two experimental results of concretecylinders and reinforced concrete columns. For both tests, SMA wires of NiTiNb andNiTi are used to confine concrete using residual stress. The SMA wire jackets onthe concrete cylinders increase the peak strength and the ductility compared tothe plain concrete cylinders. In addition, the SMA wire jackets on reinforcedconcrete columns increase the ductility greatly without flexural strength degradation.

Two-way Shape Memory Effect and Mechanical Resonance Properties of Shape-Memory-Alloy-Coated Magnetic Ribbons

This paper describes a new type of actuator composed of a shape-memory-alloy coated magnetic ribbon that detects any deformation of the shape memory alloy. The ribbons reversibly deform by heating or cooling in the temperature region from 10°C to 80°C. The deformation causes a change in the mechanical resonant frequency, which can be detected wirelessly with a pick-up coil. The deformation of the ribbons is confirmed to be proportional to the mechanical resonant frequency with an accuracy of ±0.58%. A heat-driven actuator with a high positioning resolution will be realized by monitoring the resonant frequency and feeding back it to the heating power.

S0303-2-6 粉末冶金プロセスによるTi-Ni-Zr高温形状記憶特性の作製(形状記憶合金の特性と応用展開(2))

Ti-Ni-Zr shape memory alloys were fabricated by powder metallurgy (P/M) process. The effects of fabrication conditions on the microstructure and shape memory characteristics of Ti-50.2mol%Ni-5mol%Zr alloy were investigated. Two types of powders were fabricated by mechanical alloying. Elemental Ti, Ni and Zr powders were mixed by a planetary ball mill at a rotational speed of 500 rpm for milling times of 0.6 ks (mixed powder) and 720 ks (alloyed powder). In the case of the alloyed powder, the microstructure of the as-sintered alloy was homogeneous. The transformation temperatures of the alloy showed higher than those of the wrought alloy. But the alloy showed no shape memory effect and poor tensile property due to contamination of the alloyed powder. The alloy of the mixed powder solution-treated at 1173 K had shape memory effect. The shape recovery property of the alloy was stabilized due to the cycle of heating after loading.

Fabrication of Ti-Ni-Zr Shape Memory Alloy by P/M Process

This work focuses on the fabrication of Ti-Ni-Zr high-temperature shape memory alloy by powder metallurgy (P/M) process. The effects of fabrication conditions on the microstructure and shape memory characteristics of Ti-50.2 mol%Ni-5 mol%Zr alloy were investigated. In this research, elemental Ti, Ni and Zr powders were used. These powders were mixed by a planetary ball mill at a rotational speed of 500 rpm for milling times of 0.6 ks (mixed powder) and 720 ks (MAed powder). The mixtures were sintered by a pulse-current pressure sintering equipment at 1153 K for sintering times of 1.8 ks and 1.2 ks. The solution treatment was carried out at various temperatures between 1073 K and 1273 K to homogenize the microstructure of the as-sintered alloy. The microstructure of the alloy became more homogeneous with an increase in solution-treatment temperature. In the case of the mixed powder, however, Zr-rich phases were observed in the microstructure of the solution-treated alloy. The alloy solution-treated at 1173 K showed a yielding behavior in the stress-strain curve, and the tensile strength and elongation of the alloy were more than 350 MPa and 2.5%, respectively. On the other hand, in the case of the MAed powder, the microstructure of the as-sintered alloy was homogeneous. The P/M alloy showed higher transformation temperatures than those of the wrought alloy. But, the alloy showed no shape memory effect and poor tensile property due to contamination of the MAed powder.

Shape memory effects of polyurethane block copolymers cross-linked by celite

The shape memory polyurethane (PU) copolymers cross-linked by celite, a porous inorganic material with enormous surface area and hydroxyl groups on the surface, were prepared to see if the shape memory effect and the mechanical properties were improved. The PU copolymers with different celite contents were compared and characterized by IR, DSC, DMA, and UTM. The melting temperatures of PU soft segment were around 20 oC independent of celite content. The shape memory effect and mechanical properties were dependent on the celite content, and the celite addition into the reaction mixture should be made in the middle of polymerization to get the best shape memory and mechanical properties. The best mechanical properties were found at 0.2 wt% celite content and its shape retention rate went up to 98 %. The inclusion of celite as a cross-linker increased both shape memory effect and mechanical properties. The reasons underlining the improvements by adopting celite as a cross-linker are discussed in this paper.