Properties Of Shape Memory Alloys Research Articles

Nonlinear dynamics of earthquake-resistant structures using shape memory alloy composites

Earthquake-resistant structures have been widely investigated in order to produce safe buildings designed to resist seismic activities. The remarkable properties of shape memory alloys, especially pseudoelastic effect, can be exploited in order to promote the essential energy dissipation necessary for earthquake-resistant structures. In this regard, shape memory alloy composite is an idea that can make this application feasible, using shape memory alloy fibers embedded in a matrix. This article investigates the use of shape memory alloy composites in a one-story frame structure subjected to earthquakes. Different kinds of composites are analyzed, comparing the influence of matrix type. Both linear elastic matrix and elastoplastic matrix with isotropic and kinematic hardening are investigated. Results indicate the great energy dissipation capability of shape memory alloy composites. A parametric analysis allows one to conclude that the maximum shape memory alloy volume fraction is not the optimum design condition for none of the cases studied, highlighting the necessity of a proper composite design. Despite the elastoplastic behavior of matrix also dissipates a considerable amount of energy, the associated residual strains are not desirable, showing the advantage of the use of shape memory alloys.

Comparison of Bending Fatigue of NiTi and CuAlMn Shape Memory Alloy Bars

The behaviour under cyclic bending and in particular the fatigue properties of shape memory alloy (SMA) bars are important for civil engineering applications. In this paper, structural and functional fatigue is studied for both NiTi‐ and copper‐based shape memory alloys. The results are presented from cyclic bending tests on 7 mm diameter NiTi and 12 mm diameter CuAlMn SMA bars targeted at 100,000 cycles. During the tests, dynamic loading at 1 Hz, 5 Hz, and 8 Hz was applied for different strain levels (0.5%, 1%, 2%, and 6%). The stress‐strain curve, damping ratio, and secant stiffness were analysed for material characterisation, and the evolution of these parameters was studied to assess functional fatigue. The fatigue life is extended dramatically when the strain is below 1%, and the structural fatigue life of CuAlMn is shown to be better than that of NiTi and to depend on the loading rate. However, decay in stiffness can be found in the CuAlMn SMA, which is considered to be caused particularly by its long grain boundary.

Shape memory alloy heat activation: State of the art review

The use of shape memory alloys (SMAs) in civil structures attracted the attention of researchers worldwide. This interest is due the unique properties of SMAs, the shape memory effect (SME) and pseudoelasticity. Other desirable attributes for SMA include biocompatibility, high specific strength, wear resistance, anti-fatigue characteristics, and high yield strength. These beneficial qualities allow for a wide range of applications ranging from aerospace field to the medical and civil engineering fields. To intelligently utilize shape memory alloys and widen their application potential, certain characteristics including the heat activation and heat transfer mechanisms must be thoroughly understood. Such understanding would allow the development and optimization of systems utilizing SMA. Hence, this paper presents a state-of-the-art review about shape memory alloys with specific focus on the heat activation mechanisms and the heat transfer modes.

Effect of tensile loading rate on interfacial properties of SMA/polymer composites

In the present paper, the effect of loading rate on the interfacial properties of shape memory alloy (SMA) reinforced polymer composites is investigated using experiments and theoretical methods. First, experimental pull-out tests were performed at three different loading rates with the crosshead speeds of 0.3, 25 and 400 mm/min. The effect of loading rate on the tensile properties of SMA wires was also examined using tensile tests. For each loading rate, three pre-strain levels (0, 2 and 4%) were considered. A previously developed theoretical model was modified to determine the effect of loading rate on the interfacial behavior between SMA wires and polymer. According to results obtained, increasing the loading rate led to a reduction in the tensile strength and Young's modulus of SMA wires. On the other hand, interfacial shear strength between SMA and polymer was improved in higher loading rates. Enhancement of 70% was obtained for the interfacial shear strength at 400 mm/min in comparison with 0.3 mm/min crosshead speed. By comparing the results of the theoretical model and experiments good agreement was obtained. Moreover, the optical microscopy was utilized to investigate the effect of the generated recovery force in SMAs, on the compressive zone in SMA/polymer specimens.

Proposed SMA Tension Sling Damper for Passive Seismic Control of Building

Passive Shape Memory Alloy (SMA) based Tension Sling Damper (TSD) is proposed to control seismic response of building represented as dynamic SDOF system. Non-linear hysteretic behavior of SMA is characterized by Tanaka model with seismic excitations as input. It is converted to equivalent piece-wise linear elastic viscous damping model described by stiffness constant ‘keff’ and damping constant ‘ceff’ to implement it with linear dynamic system. Damping constant ‘ceff’ is evaluated for TSD for given seismic excitation at each instance of time defined as instantaneous damping, unlike constant damping used in other studies, to derive accurate seismic response of the dynamic system. Seismic response control parameters – peak and rms perfor-mance indices (PI) for displacement and acceleration, peak damper force, maximum damping ratio are evalu-ated for flexible, moderately stiff and stiff dynamic systems fitted with TSD under pulse and strong ground motion type seismic excitations with varied PGA. Substantial reduction in PI is observed for controlled systems through varying design parameters of TSD – cross-sectional area and length of SMA sling. TSD yields better seismic response control for moderately stiff and flexible system due to super-elastic properties of SMA. Fur-ther, it works efficiently for seismic excitations with low to moderate PGA.

Ductility Analysis of Beams Reinforced with Super Elastic Shape Memory Alloys

Ductility of the beam is important phenomenon while calculating the strength of any structure. This paper discusses the ductile behavior of beam reinforced with super elastic shape memory alloys. Before initiating the experimental program preliminary properties of shape memory alloys (SMA) were defined and concrete properties are defined by casting standard cubes. Experimental program consists of two point load test on a beam reinforced with SMA. Beam is loaded to know the ultimate deflection. Load deflection characteristics and deformation of the beam are analysed to study the ductile characteristics.

A New Type of SMA Self-reset Damper and Its Performance

This paper develops a new self-resetting energy-saving support of SMA based on the unique superelastic properties of shape memory alloy (SMA) through independent innovation in order to reduce the effect of earthquakes on engineering structures. Experiment and data analysis of the deformation, energy consumption and self-reset performance of this new structure are investigated shows that that the supporting device can stably exert the functions of energy consumption and self-reset under the tension and compression cyclic load;. This paper also explores the influence of loading rate and displacement amplitude on energy consumption of the supporting device, thus further expanding the application of SMA in civil engineering.

Dissecting the influence of nanoscale concentration modulation on martensitic transformation in multifunctional alloys

Nanoscale concentration modulation (CM) is a novel and effective approach of manipulating martensitic transformations (MTs) for developing next-generation high-performance shape memory alloys (SMAs). Spinodal decomposition is one of the most economic methods to obtain bulk compositionally modulated materials for practical applications. The wavelength, amplitude, and statistical distribution of CM generated by spinodal decomposition are tunable via adjusting the aging temperature, or the aging time. However, how these features influence the effect of CM on MTs still remains largely unexplored. In this study, theoretical analyses and computer simulations are combined to dissect the influence of these features on the kinetic process of MTs and mechanical properties of SMAs. The findings of this study provide insights and guidance on the design of SMAs for desired mechanical properties via CM engineering. Moreover, the findings are applicable to not only SMAs but also other materials that have MTs, e.g. steels and high-entropy alloys.

Multi-Physics Bi-Functional Intelligent Meta-Device Based on the Shape Memory Alloys

Transformation theory, succeeding in multiple transportation systems, has enlightened researchers to manipulate the field distribution by tailoring the medium’s dominant parameters in certain situations. Therefore, the science community has witnessed a boom in designing metamaterials, whose abnormal properties are induced by artificial structures rather than the components’ characteristics. However, a majority of such meta-devices are restricted to the particular physical regimes and cannot sense the changes taking place in the surrounding environment and adjust its functions accordingly. In this article we propose a multi-physics bi-functional “intelligent” meta-device which can switch its functions between an invisible cloak and a concentrator in both thermal and DC electric conduction as the ambient temperature or voltage varies. The shape memory alloys are utilized in the design to form a moveable part, which plays the crucial role in the switching effect. This work paves the way for a practicable method for obtaining a controllable gradient of heat or electric potential, and also provides guidance for efficiently designing similar intelligent meta-devices by referring to the intriguing property of shape memory alloys.

Applicability of Shape Memory Alloys in Aircraft Interiors

This paper evaluates possible applications for SMAs (Shape Memory Alloys) based on the requirements in the field of aircraft interiors. The authors gather requirements regarding industry standards and regulations by detailed literature research and lead user interviews. They develop a classification scheme for SMA-based actuators, which consists of SMA-specific technical attributes and requirements. This classification scheme allows one to evaluate the feasibility of using SMA-based systems in aircraft interiors. Furthermore, this paper clusters critical requirements and discusses solutions for limitations of SMAs in aircraft interiors. The authors identify critical and noncritical requirements for the implementation of SMA-based actuators. They suggest solutions for critical requirements in order to improve the possible range of applications for SMAs. The study exclusively regards the field of aircraft interiors and the currently existing industry standards and only indirectly takes laws into account. The evaluated requirements and proposed solutions can be transferred to other areas such as the automotive industry. This structured analysis of the feasibility of SMA-based systems in aircraft interiors is an innovative research work and, therefore, is valuable in order to benefit from the advantageous properties of SMAs.

A dual-pillar method for measurement of stress-strain response of material at microscale

A dual-pillar method is proposed to determine nonlinear stress-strain relation and mechanical properties of shape memory alloy at microscale. Two neighboring cuboidal micropillars of the same cross-sectional area but different heights are fabricated and compressed by flat-tip nanoindentation. An accurate stress-strain response of the middle uniformly deformed part of the long pillar is obtained by subtracting the measured displacement of the short pillar from that of the long pillar to remove the top and bottom effects. Finite element analysis confirmed the effectiveness of the developed dual-pillar method in removing the effects of substrate deformation and stress concentration in single-pillar compression. This method is also valid to other materials and to tensile loading condition.

Development of an Energy Efficient Diaphragm Pump with a Nickel Titanium Diaphragm

A new pump design is proposed that uses special properties of shape-memory alloys. The use of nickel titanium as the diaphragm material improves equipment reliability and the efficiency of the oil production plant, as well as allows to reduce the equipment size.

Sensitivity analysis and multi-criteria optimization of SMA cable restrainers for longitudinal seismic protection of isolated simply supported highway bridges

Considering the flexibility of isolation bearings, isolated bridges are susceptible to unseating problems or even collapse due to excessive displacement under strong earthquakes. Shape memory alloy (SMA) wires can be utilized as seismic restrainers to confine this displacement. Recently, a design procedure for SMA restrainers has been proposed based on a linearized two degree-of-freedom analytical model. The key design parameters include three geometric factors (the ratio of the allowable displacement to the seat width, Δa/Lsw, horizontal angle, θ0, and normalized elongation parameter α), and three factors related to material properties of SMA (the maximum applied strain, εmax, the elastic modulus, E0, and the austenite to martensite start stress, fy,SMA). The objective of this study is to optimize the design procedure by evaluating the effect of each design factor on the seismic response of an isolated bridge which is retrofitted by SMA restrainers. After conducting a one-half fractional factorial analysis, it was found that the material factors have slight impact on the relative displacement between the pier and the girder, and the base shear of the pier, with percentage contributions smaller than 4% and 13%, respectively. Then, a full factorial analysis is followed through a multi-criteria decision making process in order to optimize the SMA restrainer. The results show that the optimal value of Δa/Lsw, which effectively reduces the relative displacement and simultaneously control the base shear of the piers, is 0.4; the optimum value of θ0 ranges from 0 to π/4; and the most effective value of α is 1.0.

Use of Magnetic Induction to Activate a “Touchless” Shape Memory Alloy Implantable Penile Prosthesis

IntroductionWe describe a novel physiologic penile prosthesis that uses shape memory alloy properties to mimic the transition between a flaccid and erect penis using magnetic induction instead of hydraulic pressure. AimTo evaluate the parameters of magnetic induction to activate a shape memory alloy implantable penile prosthesis. MethodsWe prototyped an implantable penile prosthesis cylinder using temperature-tuned nickel titanium alloy tubes laser cut to specifications.The device was then tested implanted in an animal tissue model and in cadaveric tissue. Testing consisted of placing the device deactivated in its more malleable and compressed state, then activating it using an external inducer wand while measuring temperature changes that occur on the surface of the device, within the tissue, and at the skin surface. Main Outcome MeasuresOur main outcome measures were the efficiency of activation and thermal safety of this approach. ResultsUsing a handheld magnetic inductor, we were able to successfully activate the SMA penile prosthesis with no direct contact under 45 seconds. This handheld wand produced a magnetic field that penetrated tissue and caused the appropriate phase change within the prosthesis. Tissue temperature (middle and surface probes) in the animal tissue model increased only a few degrees Celsius during the activation process, and never exceeded 28 degrees Celsius from a baseline at room temperature ∼ 25 degrees Celsius. We encountered similar results without a notable change in tissue temperature in the cadaveric tests. The fully activated device resisted buckling forces of 2.66 kgf ± 0.045. Clinical ImplicationsThis non-hydraulic shape memory prosthesis obviates the needs for reservoirs and pumps, and the wand-based interaction with the device may be easier to use. Strength & LimitationsThis technology represents a fundamental departure from the hydraulic-based penile prosthesis and has comparable mechanical properties as current-marked devices. It appears to show thermal safety in controlled environments, however real-world use would need further studies. Further optimization of prototypes needs to be done prior to human clinical trials. ConclusionA shape memory penile prosthesis is a promising alternative to hydraulic-based penile prostheses and can be activated safely and efficiently using magnetic induction in our models of the human penis.Le BV, McVary KT, McKenna K, et al. Use of Magnetic Induction to Activate a “Touchless” Shape Memory Alloy Implantable Penile Prosthesis. J Sex Med 2019;16:596–601.

Thermomechanical processing effects on the structure and properties of Fe-based SMAs. I. Evolution of phase structure

The paper analyses the effects of heat treatment (HT) and mechanical alloying (MA) on the evolution of phase structure of an Fe-Mn-Si-Cr-Ni Shape Memory Alloy (SMA) obtained by powder metallurgy (PM). Using various amounts of mechanically alloyed (MA’ed) powders, namely 0 and 40 vol. %, two groups of specimens with chemical composition Fe-14Mn-6Si-9Cr-5Ni (mass.%) were produced by PM. After blending, pressing, sintering and hot-rolling, each set of samples was subjected to five different heat treatment temperatures 973, 1073, and 1373 K, respectively. Tensile pre-straining tests were performed on all samples, with increasing pre-straining degrees up to 4.5 %, in order to stress-induce ε (hcp) martensitic phase in the material. Structural analysis was implemented by means of X-ray diffraction and SEM observations. XRD and SEM investigations revealed the formation of thermally induced α’-bcc martensite, besides ε-hcp, as a particularity of this powder metallurgy, mechanically alloyed, shape memory alloy.

Thermomechanical processing effects on the structure and properties of Fe-based SMAs. II. Evolution of damping behavior

The present paper analyses the effects of five different heat treatment temperatures, between 973, 1073, … and 1373 K as well as two mechanical alloying (MA) fractions, 0 and 40 vol. %, on the evolution of damping behavior of an Fe-Mn-Si-Cr-Ni Shape Memory Alloy (SMA) obtained by powder metallurgy (PM). From the 10 types of samples, rectangular specimens were cut by wire-spark erosion for dynamic mechanical analysis (DMA) tests. DMA tests were performed by temperature scans (TS) and strain sweeps (SS). TS were applied between room temperature (RT) and 673 K, at constant amplitude, and thus enabled determining the temperatures of internal friction maxima associated with antiferromagnetic-paramagnetic transition (Néel temperature), , and ε-martensite reversion to γ-austenite, , as a function of MA’ed fraction and HT temperature. SS were applied during three cycles with increasing strain amplitude and performed at three temperatures: (i) T1=RT; (ii) and (iii) . The effects of HT temperature and MA’ed fraction on storage modulus (E’) values were emphasized for each of the three temperatures T1,2,3. An E’-plateau was observed and associated with the formation of ε stress induced martensite, during DMA-SS.

The main characteristics and application of the shape memory alloys in orthodontics and endodontics

Summary Main characteristics of shape memory alloys (SMA) based on equiatomic nickel-titanium (TiNi) composition and their application in endodontics were analyzed in this paper. Particularly, phase transition between cubic body centered austenite phase and orthorhombic or monoclinic martensite phase was studied. Besides, main drawbacks of the conventional technology of SMA production were given, as well as a new technology approaches in enhancement of SMA properties, without changes of their super-elasticity.

Application of Virtual Reality for Learning the Material Properties of Shape Memory Alloys

A shape memory alloy (SMA) is an alloy which can eliminate deformation at lower temperatures and restore its original shape upon heating. SMAs have been receiving considerable attention in the research field of materials science, and their applications include robotics, automotive, aerospace, and biomedical industries. Observing the SMA’s shaping and restoration processes is important for understanding its working principles and applications. However, the transformation of its crystal structure with temperature can only be seen using special equipment, such as a transmission electron microscope (TEM), which is an expensive apparatus and the operation requires professional skills. In this study, a teaching module is designed using virtual reality (VR) technology and research results of an SMA to show its shape memory properties, shaping and restoration processes, as well as the real-life applications in an immersive and interactive way. A teaching experiment has been conducted to analyze students’ learning effectiveness using the teaching module (the experimental group) compared with that of using real SMA materials as the teaching aids (the control group). Two classes of students in the Department of Materials Science (one as the experimental group and the other as the control group) were selected as the samples by convenience sampling from a university in North Taiwan. The experimental group contained 52 students and the control group contained 70 students. A nonequivalent pretest-posttest design was adopted to explore whether the two groups had a significant difference in learning effectiveness. The experimental results reveal that the teaching module can improve the learning effectiveness significantly (p = 0.001), and the questionnaire results also show that a majority of the students had positive attitudes about the teaching module. They believed that it could increase their learning motivation and help them understand the properties and applications of the SMA.

Application of Shape Memory Alloys in Historical Constructions

ABSTRACTA device prototype, based on the superelastic properties of Shape Memory Alloys (SMAs), is proposed to enhance the thermal and seismic behavior of steel tie-rods. First, the thermal behavior of steel tie-rods with and without SMAs is presented based on the results of extensive experimental tests in thermal room. Next, the seismic performances of the proposed SMA system are discussed based on the results of a series of shaking table tests on a 1:4-scale timber roof truss model. In this article, the functioning principles of the proposed SMA-based device prototype are illustrated and the main aspects related to its implementation in practice are discussed in detail. Finally, a recent example of application of the proposed technology to a historic single-aisle church, realized in the 13th century in Brindisi (southern Italy), and equipped with inadequate and deteriorated steel tied rods, is shown.

NiTi shape memory alloy helixes through the hydriding–dehydring method

Shape memory alloys have been adopted in many industries, including the biomedical and electronic industries, due to their unique properties. Actuator design is one of the areas in which the thermomechanical properties of shape memory alloys have played a major role in technological advances. Helical spring shape memory alloy actuators, a common type of actuator, are generally made by torsional loading of a straight wire; however, a stress concentration can result from the loading leading to a reduction of the recovery force. In this study, a low pressure hydriding–dehydriding method for producing shape memory alloy helixes from wires is presented. The helix pattern was obtained by hydrogen charging NiTi shape memory alloy 500 µm diameter wires for different time intervals, where the wires are embrittled and go through martersite-to-austenite phase transformation resulting in a helical crack. The wire hydrogen charging is then followed by dehydriding to remove the hydrogen. The wires and resulting helixes were characterized using scanning electron microscopy, differential scanning calorimetry, and synchrotron x-ray radiation diffraction. The relationship between the dimensions of the helixes and charging time was investigated.