Superelasticity Effect Research Articles

Superelasticity and elastocaloric effect of Ti-rich TiNi shape memory ribbon

As-spun Ti-rich Ti50.9Ni48.9Si0.2 ribbon showed recoverable superelastic strain of 4.5%, which was associated with elastocaloric cooling of 11.3 K. Cyclic superelastic tests showed that the ribbon exhibited great functional stability. The experimental results demonstrated that the melt-spinning process could improve the functionality of TiNi shape memory alloy.

TiNi Alloy Lattice Structures with Negative Poisson’s Ratio: Computer Simulation and Experimental Results

One of the issues that modern implants face is their high stiffness, coupled with a positive Poisson’s ratio along the implant. This creates certain problems with bone inflammation and implant detachment. A possible solution to these problems is TiNi alloy lattice structure implants with low stiffness and negative Poisson’s ratio. This paper presents the results of simulation, fabrication by the SLM technique, and study of lattice structures with negative Poisson’s ratio, which can help to solve said problems. The studies involve the determination of mechanical characteristics, Poisson’s ratio, transformation temperatures, and the potential for a superelasticity effect of the lattice structure. The characteristics obtained at initial simulation were partially confirmed in the course of the works. Moreover, the possibility of fabricating TiNi alloy lattice structures with negative Poisson’s ratio (about −0.00323) and low Young’s modulus values (0.818 GPa) was confirmed by the SLM technique.

Study on Damping Performance of Hyperboloid Damper with SMA-Negative Stiffness

To improve the limiting capacity of isolation bearings and reduce residual deformation, a new material shape memory alloy (SMA) was introduced into the damping device. SMA shape memory materials have shape memory effect, superelastic effect, and damping properties of metal alloys. Although the SMA isolation bearing can improve the self-resetting ability of the bridge, it will increase the internal force response of the substructure compared with the ordinary isolation bearing. To solve this problem, a new type of SMA negative stiffness hyperboloid shock absorber is proposed. The device is provided with restoring force by SMA cables, negative rigidity by two friction pendulum supports with opposite curved surfaces, and energy dissipation capacity by friction between the slider and the upper and lower steel plates. Theoretical derivation and finite element analysis results show that the damping device can not only provide the self-resetting ability of the bridge but also partially reduce the internal force response of the SMA damping bridge structural system on the premise of reducing the displacement response of the bridge.

Calculation Model of Mechanical and Sealing Properties of NiTi Alloy Corrugated Gaskets under Shape Memory Effect and Hyperelastic Coupling: Two Sealing Properties.

Bolted flange connections are commonly used in process industries. Their sealing performance is greatly affected by the gasket. In this paper, a NiTi alloy corrugated gasket was simulated to reveal its sealing performance, considering the gasket surface roughness, shape memory effect and superelastic effect. A fluid–structure coupling analysis method that takes the real surface morphology of the gasket contact zone was proposed, and a leakage rate prediction model was established. The results showed that NiTi shape memory effect could enhance the sealing reliability in service and lower the leakage rate. The leakage rate of the NiTi alloy corrugated gasket is positively correlated with the internal pressure of the medium and the roughness of the sealing surface. The prediction model of the NiTi alloy corrugated gasket leakage rate has good reliability with an average error of about 16.81% compared with the simulation.

Advanced and emerging materials for testing a curtain wall connection element for improved seismic performance

The research for emerging and disruptive new materials and advanced technologies is a driver of technological innovation in both industry and academia. In this work, the authors present some parts of the results of their research and investigation. The experimental research of advanced materials is a constantly evolving field, concerning the need to respond to increasingly advanced technical performance, even in the construction sector and specifically for Building Envelopes. In this context, the contribution concerns ongoing experimental research, which investigates the dynamic behavior of non-structural elements of the Facade subjected to the action of the earthquake. The results of the investigations conducted so far aim to increase innovation in the field of advanced materials for extreme applications, for the constraints on the implementation of the technologies (increasing element sizes, higher mechanical strengths, better performance), exploiting the superelastic effect (SE) and the shape memory effect (SME). Thus, it seems clear that the potential of the two unique properties for Facade Design applications is a valuable tool for investigating dynamic behaviors that exist in nature as well.

Influence of processing parameter on phase transformation and superelastic recovery strain of laser solid forming NiTi alloy

NiTi alloys with superelasticity and shape memory effects are currently widely used because of its excellent deformation recovery ability, mechanical strength, and biocompatibility. The Ni 50.8 Ti 49.2 alloy was manufactured by using laser solid forming (LSF) technology with pre-alloyed powder in this work. The microstructure, phase transformation and shape recovery of the deposited alloy were influenced by the parameters used in depositing process. The as-deposited Ni 50.8 Ti 49.2 alloy formed by LSF is columnar crystals epitaxially grown along the deposition direction, with a small amount of equiaxed crystals appear between the deposition layers. Two-step/multi-step martensitic transformation occurs in the deposited Ni 50.8 Ti 49.2 alloy. The martensitic transformation temperature slightly changes with the deposition height, whereas the R transformation temperature basically does not change with the deposition height. In the test of the mechanical properties, sample with a laser power of 1700 W and a scanning rate of 680 mm/min has a compression superelastic recovery as high as 9.5%. Moreover, Ti 2 Ni precipitated phase and R phase appeared in all samples, but only the precipitated Ti 2 Ni and R phase in this sample had a certain orientation relationship with the matrix. Shape memory characteristics was also tested by compression deformation, and the maximum recovery strain of shape memory effect is 6.1%, which is obtained in the sample deposited with 1500 W laser power and 480 mm/min scanning rate. • Columnar crystals grow along the deposition direction in LSF Ni 50.8 Ti 49.2 alloy. • Superelastic recovery as high as 9.5% was obtained in LSF Ni 50.8 Ti 49.2 alloy. • Orientation relationship of precipitation with matrix leads to high recovery rate.

Influence of Wire Geometry on the Mechanical Behavior of the TiNi Design

The present article is aimed at studying the deformation behavior of TiNi wire and knitted metal TiNi mesh under uniaxial tension and revealing the role of wire geometry on their main mechanical characteristics and mechanisms of deformation behavior. The temperature dependence curve of the electrical resistance indicates that a two-stage martensitic transformation of B2→R→B19′ is occurring, and is responsible for the superelasticity effect. The TEM results showed that at room temperature, the TiNi wire has a nanocrystalline structure composed of B2 austenite grains. A change in the deformation mechanism was established under the uniaxial tension, where the TiNi wire exhibits the effect of superelasticity, while the knitted metal TiNi mesh made from this wire is characterized by hyperelastic behavior. Fracturing of the knitted metal TiNi mesh requires significant loads of up to 3500 MPa compared to the fracture load of the TiNi wire. With the uniaxial tension of the wire, which maximally repeats the geometry of the wire in knitted metal mesh, an increase in mechanical characteristics was observed.

Design of a Morphing Skin with Shape Memory Alloy Based on Equivalent Thermal Stress Approach.

Shape memory alloy (SMA) is one of the potential driving devices for morphing aircraft due to its advantages of pseudoelasticity, superelasticity, and shape memory effect. Precise and fast analysis of SMA has simultaneously become a key requirement for industrial applications. In this study, a user-defined material subroutine (UMAT) was implemented and successfully applied in a three-dimensional numerical simulation in ABAQUS based on the extended Boyd–Lagoudas model. In addition to the conventional detwinned martensite (Md) and austenite (A), twinned martensite (Mt) was also considered to model the practical transformation accurately. Then, the equivalent thermal strain approach was adopted to simplify the simulation complexity with UMAT. By resetting the thermal expansion coefficient, the thermal strain equivalent to the original phase transformation strain was generated. The approach was validated in two cases, showing consistent results with the extended Boyd–Lagoudas model and reduction in time consumption by 89.1%. Lastly, an active morphing skin integrating the single-range SMA and a stainless-steel plate was designed to realize two-way morphing. The calculated arc height variation of the skin was 3.74 mm with a relative error of 1.84% compared to the experimental result of 3.81 mm. The coupled use of UMAT and the equivalent thermal stress approach helped to reduce the challenge in modeling SMA.

Effect of a constant laser energy density on the evolution of microstructure and mechanical properties of NiTi shape memory alloy fabricated by laser powder bed fusion

As the key parameter in the laser powder bed fusion (L-PBF), the laser energy density can directly determine the comprehensive quality of NiTi shape memory alloys (SMAs). However, the specific role of laser parameters under the energy density value is rarely discussed. In this work, the effect of specific laser power and scanning speed variation on the properties of NiTi alloy under the same energy density (62.5 J/mm3) was studied. Results show that the phase transformation temperatures decrease as the Ni content was increasing with the simultaneous increases in laser power and scanning speed. Under the influence of Ni content, the SMA samples with low phase transformation temperatures were fully austenite at room temperature. In the cyclic compression test at Af + 15 °C, the sample built under the lowest laser power and scanning speed showed the best superelasticity effect. Higher scanning speed resulted in a stronger <100>//BD texture, and the increase of laser power produced a deeper molten pool, which remelted the solidified part at the bottom and further enhanced the <100>//BD texture. The TEM characterization shows that more Ni4Ti3 precipitates with larger sizes are obtained in the sample with the lowest laser power and scanning speed. The finite element analysis shows the lowest peak temperature in the molten pool under the lowest laser power and scanning speed, which can promote the precipitation of Ni4Ti3 particles. The promoted formation of Ni4Ti3 precipitates enhanced the austenite stability and further enhanced the superelasticity of NiTi alloy fabricated at the lowest laser power. The present work shows that the specific laser parameter under the constant energy density value can further improve the comprehensive performance of L-PBF NiTi SMAs.

Ultra-wide-temperature-range superelasticity and intrinsic two-way shape memory effect in Co–Ni–Ga microwires

We demonstrate perfect superelasticity and inherent two-way shape memory effect in Co49Ni21Ga30 microwires fabricated by a Taylor–Ulitovsky method. With the formation of an almost complete [001]A-oriented single crystal along the axis of the wire, the as-drawn microwire displays great superelastic behaviors with a large reversible tensile strain of &amp;gt;8% over an ultra-wide temperature window of 550 K (223–773 K). Simultaneously, an excellent intrinsic two-way shape memory effect with a considerably large strain output (∼6.3%) was also obtained in this Co49Ni21Ga30 microwire. After mechanical training, the two-way shape memory strain can reach up to 6.8% at a low operating temperature. With the combination of above extraordinary functional properties and the low cost of fabrication, the Co49Ni21Ga30 microwire holds a significant potential for applications in miniature sensing and self-actuating devices in the future.

Effect of Pore Shape on Mechanical Properties of Porous Shape Memory Alloy

Porous shape memory alloys (SMAs) have been widely used in the aerospace, military, medical, and health fields due to its unique mechanical properties such as superelasticity, biocompatibility, and shape memory effect. In this work, the pore shape was considered in the constitutive model of the porous SMAs by respectively introducing the parameter of aspect ratio and for different pore shapes including oblate, sphere, and prolate shapes, so the expression of Young’s modulus for the porous SMA can be derived. Then, the constitutive model for such a porous shape memory alloy was established. When the porosity was zero, the model can be degenerated to the dense case. The stress–strain curves for the porous SMA with a porosity of 13% with different aspect ratio are then given. Numerical results showed good agreement with the published experimental data that proved the validation of the model. Based on the proven constitutive model, the properties of porous SMA with different porosity and pore shapes are discussed. The results showed that the pore shapes and the porosities had a big effect on the stress–strain curves for the porous shape memory, while with the increasing porosities, the Young’s modulus and the hysteresis both decreased. With the same porosities, the Young’s modulus and hysteresis loop of SMA with round pores were the largest, while the Young’s modulus and hysteresis loop were the smallest when , and they were greater when than when . It can be seen that the closer to the circle, the better the performance of the material.

Ferroelastic oligocrystalline microwire with unprecedented high-temperature superelastic and shape memory effects

A compelling demand exists for high-performance high-temperature shape memory alloys (HTSMAs) that can be applied as intelligent components in the rapidly developing aerospace, robotics, manufacturing, and energy exploration industries. However, existing HTSMAs are handicapped by their high cost and unsatisfactory functional properties, which impede their practical application. Here, by using the strategy of creating an oligocrystalline structure, we have developed a high-performance, cost-effective high-temperature shape memory microwire exhibiting an exceptional combination of superb superelasticity with a large recoverable strain of up to 15%, an outstanding one-way shape memory effect with a maximum recoverable strain as high as 13% and a remarkable two-way shape memory effect with a large recoverable strain of 6.3%. These unparalleled comprehensive properties provide this microwire with a high potential for use in high-temperature actuation, sensing, and energy conversion applications, especially in miniature intelligent devices, such as high-temperature microelectromechanical systems. The present strategy may be universally applicable to other brittle phase-transforming alloys for achieving outstanding functional properties at high temperatures.

Laser Powder Bed Fusion of Defect-Free NiTi Shape Memory Alloy Parts with Superior Tensile Superelasticity

Laser powder bed fusion is a promising additive manufacturing technique for the fabrication of NiTi shape memory alloy parts with complex geometries that are otherwise difficult to fabricate through traditional processing methods. The technique is particularly attractive for the biomedical applications of NiTi shape memory alloys, such as stents, implants, and dental and surgical devices, where primarily the superelastic effect is exploited. However, few additively manufactured NiTi parts have been reported to exhibit superelasticity under tension in the as-printed condition, without a post-fabrication heat treatment, due to either persistent porosity formation or brittleness from oxidation during printing, or both. In this study, NiTi parts were fabricated using laser powder bed fusion and consistently exhibited room temperature tensile superelasticity up to 6% in the as-printed condition, almost twice the maximum reported value in the literature. This was achieved by eliminating porosity and cracks through the use of optimized processing parameters, carefully tailoring the evaporation of Ni from a Ni-rich NiTi powder feedstock, and controlling the printing chamber oxygen content. Crystallographic texture analysis demonstrated that the as-printed NiTi parts had a strong preferential texture for superelasticity, a factor that needs to be carefully considered when complex shaped parts are to be subjected to combined loadings. Transmission electron microscopy investigations revealed the presence of nano-sized oxide particles and Ni-rich precipitates in the as-printed parts, which play a role in the improved superelasticity by suppressing inelastic accommodation mechanisms for martensitic transformation.

Effects of Microstructure on the Buckling Fatigue and Functional Degradation Characteristics of the Tape-shaped Cu-Al-Mn Shape Memory Alloy Element

Shape memory alloys (SMAs) are functional materials with high shape memory and super elasticity effects that are used in a wide range of fields, including medical and engineering fields. Our research group has focused on the negative stiffness characteristics of plate-shaped SMA during buckling deformation and has attempted to apply them to vibration-isolation devices. The buckling properties of Cu-Al-Mn SMA, which exhibits almost the same super elastic properties as Ti-Ni SMA, were evaluated in comparison with those of Ti-Ni SMA. The results showed that Cu-Al-Mn SMA is more suitable for vibration isolators because of its smaller change in post buckling properties due to temperature change and smaller hysteresis compared with Ti-Ni SMA. In addition, the buckling fatigue and functional degradation properties of Cu-Al-Mn SMA were studied. As a result, it was clarified that fatigue failure is basically caused by the propagation of cracks originating from grain boundaries, and that the increase of these cracks is the cause of the decrease in buckling load. In this study, the buckling fatigue properties of Cu-Al-Mn SMA material in which bainite phase is formed at the grain boundary by changing the heat treatment conditions were investigated, and the effects of the differences in internal microstructures on the buckling fatigue and functional degradation properties of plate-like Cu-Al-Mn SMA with different internal microstructures were compared with those of conventional Cu-Al-Mn material. The effects of different internal microstructures on buckling fatigue and functional degradation properties of plate Cu-Al-Mn SMA with different internal structures were investigated. The results show that the specimens with bainite phase have superior fatigue properties, but in terms of functional degradation properties, they increase the rate of decrease in Pcr and increase the rate of increase in tangential stiffness after buckling.

Research and Development of Applied Devices utilizing the Buckling Properties of Tape-shaped Shape Memory Alloy Elements

An elongated Shape memory alloys (SMAs) elements which shows superelastic properties can exhibit the quasi-zero or negative stiffness during post-buckling deformation. Since the buckling deformation is recovered by the superelastic effect upon unloading, the quasi-zero or negative stiffness can be used continuously. Our research group has devised, studied and reported on passive vibration isolator devices that utilize this property, but this property can be applied not only to passive vibration isolator but also to various other possible applications. This paper reports on the characteristics of a force-limiting device using the buckling properties of shape memory alloy elements, which was devised and prototyped by our research group. We also report on the newly devised convex-tape shape memory alloy element and the movement characteristics of a rehabilitation mechanism using its buckling characteristics.

Enhanced Cyclability of Superelasticity and Elastocaloric Effect in Cu and B Co-Doped Co-Ni-Ga Shape Memory Alloys

Enhanced Cyclability of Superelasticity and Elastocaloric Effect in Cu and B Co-Doped Co-Ni-Ga Shape Memory Alloys

The Influence of the Soaking Temperature Rotary Forging and Solution Heat Treatment on the Structural and Mechanical Behavior in Ni-Rich NiTi Alloy.

The structural and thermophysical characteristics of an Ni-rich NiTi alloy rod produced on a laboratory scale was studied. The soak temperature of the solution heat-treatment steps above 850 °C taking advantage of the precipitate dissolution to provide a matrix homogenization, but it takes many hours (24 to 48) when used without thermomechanical steps. Therefore, the suitable reheating to apply between the forging process steps is very important, because the product’s structural characteristics are dependent on the thermomechanical processing history, and the time required to expose the material to high temperatures during the processing is reduced. The structural characteristics were investigated after solution heat treatment at 900 °C and 950 °C for 120 min, and these heat treatments were compared with as-forged sample structural characteristics (one hot deformation step after 800 °C for a 30 min reheat stage). The phase-transformation temperatures were analyzed through differential scanning calorimetry (DSC), and the structural characterization was performed through synchrotron radiation-based X-ray diffraction (SR-XRD) at room temperature. It was observed that the solution heat treatment at 950 °C/120 min presents a lower martensitic reversion finish temperature (Af); the matrix was fully austenitic; and it had a hardness of about 226 HV. Thus, this condition is the most suitable for the reheating stages between the hot forging-process steps to be applied to this alloy to produce materials that can display a superelasticity effect, for applications such as crack sensors or orthodontic archwires.

Determination effect of two different NiTi stents on the vessel wall and studying their flexibility using finite element method

Finite element simulation is used to analysis stent designs, extension as well as interaction between a stent and a vessel. In this paper, two different stents with different geometries have been simulated. One is Zilver stent and the other one is Navalis stent. The aim of this study is to determine the effect of stents deployment with various designs that are made of shape memory alloy (SMA) on the distribution of vessel wall stresses by using computational modeling approach. The constitutive model which described the behavior of SMA is based on Microplane model. In addition, SMA stents have been simulated under torsion loading to compare the flexibility of various designs under different conditions. The superelastic behavior and shape memory effect of SMA stents are investigated in this paper. The numerical simulation results show the different geometries of stents have significant effect on the arterial wall. The results show the Navalis stent causes less stress on the arterial wall and it is more flexible than the Zilver stent under the same torsion loading.

Effect of marforming on superelasticity and shape memory effect of [001]-oriented Ni50.3Ti49.7 alloy single crystals under compression

The shape memory effect (SME) and superelasticity (SE) of Ni50.3Ti49.7 alloy single crystals were studied after quenching and marforming (deformation in the martensite phase, followed by annealing at 713 K for 0.5 h) along the [001] direction, under compression, in the high-temperature B2-phase. It was shown that marforming leads to the following: strengthening of the high-temperature B2-phase; an increase in the temperature range of SE; a decrease in the mechanical Δσ and thermal ΔТh hysteresis; and an increase in the transformation hardening coefficient Θ = dσ/dε, in comparison with the crystals after quenching. The reasons for improvements in the functional properties of [001]-oriented single crystals after marforming are discussed.

The role of texture on superelasticity and elastocaloric effect in severely rolled Ti-44Ni-5Cu-1Al (at%) shape memory alloy

The effects of crystallographic texture on the superelasticity and elastocaloric effect of nanograin Ti-44Ni-5Cu-1Al rolled sheet are investigated. Stress-strain curves with different orientation angles between tensile direction and rolling direction show that the tensile strain of the sheet is largest in rolling direction (RD) along <110> and smallest in transverse direction (TD) parallel to <100>. This texture dependence is further studied by analyzing the evolution of each strain component. With the increase of the orientation angle, intergranular constraint effect reaches the maximum in TD. As a result, transformation strain and adiabatic temperature change have a similar monotonic decreasing trend. The material coefficient of performance of the sheet reaches 11.2 in RD. This value makes it possible for severely rolled Ti-44Ni-5Cu-1Al sheet to be a potential candidate for solid-state refrigeration application at room temperature.