Shape Memory Alloy Rods Research Articles

Physics-informed deep operator network for predicting martensite evolution in superelastic shape memory alloys through cyclic tensile tests

Superelastic shape memory alloy (SMA) wires and rods possess unique deformation and energy dissipation capabilities. For the assessment of their stress response, commonly cyclic tensile tests are conducted. An important but subtle parameter in this procedure is the martensite evolution. In scenarios where conducting thermal experiments is impractical, inverse modeling from cyclic tests serves as a viable alternative. However, employing constitutive models in this process presents distinct challenges, such as parameter identification and calibration, or numerical stability issues. To address these challenges, this paper proposes a data-driven method based on a physics-informed deep operator network (DeepONet) to estimate the martensite evolution. Constraint with a stress equation, the network requires only strain–stress data for training and provides stress responses in addition to the martensite evolution. From the training data, the network learns to consider the effects included in the response. The DeepONet can be coupled with experiments to provide online estimates from noisy sensor-based strain inputs, while remaining numerically stable. Moreover, this approach avoids the need for separate parameter identification or calibration. This paper details this method and evaluates its performance through experiments conducted on superelastic SMA wires. Furthermore, as an alternative approach, training using a constitutive model is provided.

Tension-compression asymmetric functional degeneration of super-elastic NiTi shape memory alloy: Experimental observation and multiscale constitutive model

The functional degeneration of super-elastic NiTi shape memory alloy (SMA) rods is investigated in the cyclic tension-unloading and compression-unloading experiments. The results show that the functional degeneration exhibits a strong tension–compression asymmetry, which originates from the initial 〈111〉 and 〈110〉 mixed textures along the axial direction of the rods, the polarity of martensite transformation, and the complex interaction between martensite transformation and dislocation slipping. Moreover, the dependence of functional degeneration on the applied stress level is discussed. To understand and predict the effect of initial texture on the cyclic deformation of polycrystalline NiTi SMA, a multiscale constitutive model is constructed at finite deformation. At the mesoscopic scale, two major inelastic deformation mechanisms, i.e., the transformation between austenite and martensite phases and the transformation-induced plasticity caused by the strain mismatch at the austenite–martensite interface, are considered. The total deformation gradient is multiplicatively decomposed into the martensite transformation, transformation-induced plasticity and elastic parts. The deformation gradient parts at the mesoscopic scale are obtained by upscaling these physical quantities at a smaller spatial scale (i.e., the microscopic scale). The proposed model is formulated within the framework of irreversible thermodynamics. The driving forces for martensite transformation and transformation-induced plasticity are derived according to the established Helmholtz free energy and Clausius-Duhem inequality. The complex interaction between martensite transformation and dislocation slipping, and the forward/reverse inheritance of dislocations caused by the moving austenite–martensite interfaces are considered. To calculate the overall cyclic responses of polycrystalline NiTi SMA at the macroscopic scale, the developed constitutive model is implemented into the finite element software ABAQUS/Explicit using a user-defined material subroutine. A polycrystalline representative volume element is constructed by introducing the initial 〈111〉 and 〈110〉 mixed textures observed in the experiment. By comparing the simulated results with the experimental data, the capability of the proposed model to predict the texture-induced tension–compression asymmetric functional degeneration is verified, and the influence of texture type on the cyclic deformation is discussed.

Seismic Performance of an Earthquake Resilient Self-Centering Precast Reinforced Concrete Rocking Wall with External SMA Rods

ABSTRACT This research aims to propose an alternative way to provide a recentering force to a precast unbonded post-tensioned reinforced concrete rocking wall (RW) using shape memory alloy (SMA) bars. The physical and mechanical properties, such as fatigue, corrosion resistance, and large damping capacity, qualify the SMA to be at the forefront of materials used in structural engineering applications. In this study, the SMA bars replace the post-tensioned tendons to minimize the permanent deformation resulting from the system’s exposure to the lateral loading coming from the seismic events. The SMA bars are attached externally to the wall and fixed with the base to facilitate the installation process and reduce the repairing time if a failure occurs under unexpected events. The proposed system shows that the SMA rods can play the same role as the PT tendons to minimize the residual displacement while also providing an acceptable level of energy dissipation to the system.

Theoretical Analysis of the Operation of a Force Actuator with a Working Body Consisting of a Shape Memory Alloy Rod and an Elastic Displacement Body

Theoretical Analysis of the Operation of a Force Actuator with a Working Body Consisting of a Shape Memory Alloy Rod and an Elastic Displacement Body

Performance of Reinforced Concrete Shear Wall Equipped with an Innovative Hybrid Damper

The performance of simultaneous application of steel cantilever damper and Shape Memory Alloy (SMA) rods in the reinforced concrete (RC) shear wall was investigated. In this regard, the critical numerical validation of three full-scale experimental models were distinctly performed and the results were analyzed. Various aspects of numerical modelling, including material modelling assumptions, behavioural models, elements, and solution methods were compared with experimental results. Specimens considering SMA rods as well as steel cantilever damper were numerically investigated. The results illustrated that with increasing the SMA rod angle, the maximum force was decreased, and the residual displacement and dissipated energy was improved. Also, comparing the specimen results without the SMA rods and the specimen with the SMA rods showed that despite the positive effect of the SMA rods, which leads to an increase in maximum force and reduction of residual displacement, the dissipated energy was decreased

Актуатор с последовательным соединением стержня из сплава с памятью формы и упругого элемента смещения

One of the most promising applications of shape memory alloys (SMA) is their use for creating working bodies of power exciters (actuators). The working body of the actuator must perform certain movements due to shape memory phenomena (heating, working stroke of the actuator) and the accumulation of direct transformation deformations (cooling, idling of the actuator). It is known that the process of deformation of SMA during cooling occurs only in the presence of mechanical action, while the return to the original form during heating occurs in the absence of a corresponding mechanical action and even in the presence of a sufficiently large counteraction. To ensure the possibility of not only working, but also idling of the actuator, the working body of the SMA is connected to the elastic bias element so that both of these elements are deformed together. In this case, when the SMA element is heated, it is deformed due to the shape memory phenomenon, which leads to the deformation of the bias element associated with the working body and the appearance, both in this element and in the working body, of mechanical stresses that increase with the temperature of the SMA element. It is these stresses, which continue to act during the cooling of the working body, that ensure its deformation in the opposite direction at the stage of cooling of the working body and the corresponding direct transformation into SMA. In this paper, the behavior of an actuator consisting of a SMA rod and an elastic rod (an bias element) connected in series, the total length of which is assumed to be unchanged, is analytically investigated. The influence of the system parameters on the stresses in the SMA rod and the value of the working stroke of the actuator is investigated. The conditions for the implementation of the closed two way shape memory effect in this system are determined.

Reliability and reliability-based sensitivity analysis of self-centering buckling restrained braces using meta-models

This paper aims to carry out sensitivity analyses to study how the effect of each design variable on the performance of self-centering buckling restrained brace (SC-BRB) and the corresponding buckling restrained brace (BRB) without shape memory alloy (SMA) rods. Furthermore, the reliability analyses of BRB and SC-BRB are performed in this study. Considering the high computational cost of the simulation methods, three Meta-models including the Kriging, radial basis function (RBF), and polynomial response surface (PRSM) are utilized to construct the surrogate models. For this aim, the nonlinear dynamic analyses are conducted on both BRB and SC-BRB by using OpenSees software. The results showed that the SMA area, SMA length ratio, and BRB core area have the most effect on the failure probability of SC-BRB. It is concluded that Kriging-based Monte Carlo Simulation (MCS) gives the best performance to estimate the limit state function (LSF) of BRB and SC-BRB in the reliability analysis procedures. Considering the effects of changing the maximum cyclic loading on the failure probability computation and comparison of the failure probability for different LSFs, it is also found that the reliability indices of SC-BRB were always higher than the corresponding reliability indices determined for BRB which confirms the performance superiority of SC-BRB than BRB.

Tests of a novel re-centering damper with SMA rods and friction wedges

This research focused on development of a new type of re-centering damper consisting of the Ni-Ti Shape Memory Alloy (SMA) rods and friction wedges. Compared with the other existing types of SMA-based dampers, the proposed damper offers an improved energy absorption capacity. In addition, strength and deformation capacity of the proposed damper can be conveniently adjusted if needed. To verify the perceived benefits of the damper, a series of tests were performed on an experimental specimen. It was found that the proposed damper can exhibit stable hysteretic energy dissipation response and reliable re-centering performance without developing any visible damage in the damper components. The test results also show that the damper is not sensitive to the different loading protocols imposed. Beyond the experimental work, a theoretical model for the proposed damper was established and validated by the test results. The theoretical model can be used to design the damper in the future. Furthermore, a three-dimensional computer model was developed for the tested damper. The computer model was found to be able to accurately replicate the nonlinear responses of the experimental specimen. The modelling approaches and assumptions adopted in the computer model can be used for future analysis and design.

Adaptive predictive control of a novel shape memory alloy rod actuator

Shape memory alloys are among the highly applicable smart materials that have recently appealed to scientists from various fields of study. In this article, a novel shape memory alloy actuator, in the form of a rod, is introduced, and an adaptive model predictive control system is designed for position control of the developed actuator. The need for such an advanced control system emanates from the fact that modeling and controlling of shape memory alloy actuators are thwarted by their hysteresis nonlinearity, dilatory response, and high dependence on environmental conditions. Real-time identification and dynamic parameter estimation of the model are addressed according to orthogonal Laguerre functions and recursive least square algorithm. In the end, the designed control system is implemented on the experimental setup of the fabricated shape memory alloy actuator. It is observed that the designed control system successfully tracks the variable step and sinusoidal control references with startling accuracy of ±1 μm.

Development of a double-tee flange connection using shape memory alloy rods

This study investigated the out-of-plane shear performance of a newly developed shape memory alloy (SMA) connector and a commonly used shear/alignment connector. The innovation lies in developing a durable and easily installed and maintained flange-to-flange connector between precast concrete double-tee members. The proposed connector consists of a superelastic SMA curved bolt inserted into a duct that is then cast into the precast concrete member. Two types of sealant materials were used: polyurethane elastomeric sealant and nonshrink cementitious grout. The shear/alignment and SMA connectors were tested under monotonic vertical shear. The tests were conducted on 4 ft × 4 ft × 4 in. (1.2 m × 1.2 m × 100 mm) slab specimens. The resulting capacities and associated damage were summarized. Higher stiffness and lower ductility were observed for the SMA connector with nonshrink grout compared with the shear/alignment connector with polyurethane elastomeric sealant. The average stiffnesses of the SMA and shear/alignment connector specimens were 116,681 lb/in. (20,434 kN/m) and 31,300 lb/in. (5481 kN/m), respectively. The ductility of the SMA connector was improved when using polyurethane elastomeric sealant; however, more tests should be done to confirm this behavior. The SMA rod was reused in several tests through reheating of the SMA element. The shear/alignment connector cannot be reused.

Thermomechanical coupling in cyclic phase transition of shape memory material under periodic stressing—experiment and modeling

Experiment and modeling analysis are performed to study the evolution dynamics due to thermomechanical coupling in cyclic phase transformation responses of a superelastic NiTi shape memory alloy rod under periodic tensile stress. Synchronized acquisition of time evolutions in temperature and stress-strain curve of the rod were realized in the frequency range of 0.0004 ~ 4 Hz (average stress rate from 0.42 MPa/s to 4200 MPa/s). Significant frequency dependent oscillations, drifts and stabilizations in the strain, temperature and stress-strain curves are quantified and the roles of thermomechanical coupling in the observed evolution dynamics of the responses are revealed. It is found that the stress-strain responses are non-isothermal over the tested frequency range and that the evolution dynamics is quite distinct from that of displacement-controlled cyclic phase transition (Yin et al., JMPS, 2014) due to the non-prescribed heat sources and the implicit nature of the response. The evolution dynamics are modelled by two coupled non-linear governing equations to obtain numerical and approximate analytical expressions of the transient and steady-state stress-strain and temperature oscillations. It is shown that, for given material and ambient properties, the thermomechanical responses under cyclic-stressing can be divided into three regions and are essentially governed by the non-dimensional time scale tp¯ and stress Δσ¯.

Near-field earthquake performance of SC-BRBs with optimal design parameters of SMA

Self-centering buckling-restrained braces (SC-BRBs) utilizing the re-centering potential of shape memory alloy (SMA) bars are used to control the excessive residual drift response of braced frames under seismic loading. The effectiveness of SC-BRBs in controlling the seismic response of a structure largely depends on the relative strength and stiffness of SMA bars and BRB core plates. This study is focused on determining the optimum length and prestressing force levels in SMA bars to maximize the hysteretic energy dissipation and re-centering behavior of SC-BRBs and evaluating the drift response of a medium-rise braced frame under near-field earthquake excitations. The seismic performance of SC-BRBs has been numerically investigated at both component (local) and frame (global) levels using a computer software OpenSees. Both length and prestressing force in SMA rods are varied in the numerical models to evaluate the axial resistance and hysteretic energy dissipation potential of SC-BRBs. The hysteretic response of SC-BRBs is compared with that of conventional BRBs. Nonlinear dynamic analysis has been conducted on a 9-story braced frame equipped with SC-BRBs as well as BRBs under forty near-field ground motion records. The seismic drift response of braced frames equipped with SC-BRBs with different prestressing force levels is compared with that of BRBF. Based on the findings of this study, the optimum geometric parameters of SMA bars have been proposed for the design of SC-BRBs.

Stability of Shape Memory Alloy rods under reverse phase transformation in case of initial tensile phase-structural strains

Stability of a round cross section rod of Shape Memory Alloys under reverse phase transition where the initial strain was obtained with the help of reverse loading and subsequent unloading was investigated. It was shown that the additional structural transformation connected with buckling could not take place within the framework of a given model of the constitutive equations for Shape Memory Alloys. Numerical solutions in various problem statements and concepts were obtained.

Contactless treatment for scoliosis by electromagnetically controlled shape-memory alloy rods: a preliminary study in rabbits.

To evaluate the safety and efficacy of a system aiming to correct scoliosis called "electromagnetically controlled shape-memory alloy rods" (EC-SMAR) used in a rabbit model. We heat-treated shape-memory alloy (SMA) rods to achieve a transition temperature between 34 and 47°C and a C-shape austenite phase. We then developed a water-cooled generator capable of generating an alternating magnetic field (100kHz) for induction heating. We next studied the efficacy of this system in vitro and determined some parameters prior to proceeding with animal experiments. We then employed a rabbit model, in which we fixed a straight rod along the spinous processes intraoperatively, and conducted induction heating postoperatively every 4days for 1month, while performing periodic X-ray assessments. Significant kyphotic deformations with Cobb angles of about 45° (p < 0.01) were created in five rabbits, and no complications occurred throughout the experiment. The rabbits are still very much alive and do not show any signs of discomfort. This is the first system that can modulate spinal deformation in a gradual, contactless, noninvasive manner through electromagnetic induction heating applied to SMA alloy rods. Although this study dealt with healthy spines, it provides promising evidence that this device also has the capacity to correct human kyphosis and even scoliosis in the future. These slides can be retrieved under Electronic Supplementary Material.

Stability analysis of a round cross-section rod from Shape Memory Alloys at reverse phase transition

The mechanisms that cause loss of stability of Shape Memory Alloy rods during the reverse phase transformation under a constant load for various methods of preparing the rods before starting the reverse phase transition were considered. The problem was solved for non-, singly- and twice- coupled statements and for the concepts of fixed and varied external loads taking into account the different resistance under tension and compression.

Modeling microstructure evolution in shape memory alloy rods via Legendre wavelets collocation method

Microstructures play an important role in the research on shape memory alloys (SMA). By using mathematical modeling tools to study microstructures, it is possible to predict the behaviors of these materials under applied fields. In the current paper, a thermo-mechanical model is proposed to simulate the microstructure of a SMA rod with both fixed and impact boundary conditions via Legendre wavelets collocation method. Because of the good performance of Legendre wavelets basis, this method shows excellent properties in both precision and stability. A detailed numerical algorithm is given, and the backward differentiation formula is employed to perform all the simulations in the current paper. Computational simulations are carried out to study the stress-induced phase transformation. The dynamics of microstructure evolution, presented at different temperatures, is well captured by our developed technique.

A combined experimental and numerical study on shape memory alloy rods under torsion

In this article, a study on modeling and experimental characterization of a shape memory alloy rod undergoing torsional loading is presented. According to former studies, the direction of twist is effective on the response of a shape memory alloy rod. Accordingly, we used Brinson’s improved model and adapted it for torsional loading. Referring a twist deformation in the clockwise direction to a positive twist and a twist deformation in the counter clockwise direction to a negative twist, the asymmetric response of the shape memory alloy rod is studied. The material parameters for Brinson model are derived from the experimental tests and there is a good agreement between the present asymmetric model and the experimental data. Also, material parameters are verified due to the experimental test in different temperatures. In one of the case studies, the average error of asymmetric and symmetric models with respect to the experimental test is 4% and 15%, respectively. A parametric study along with a study on the hysteresis inner loops in addition to model prediction for different temperatures is reported in the result section.

Microstructure and mechanical properties of gas tungsten arc welded Cu-Al-Mn shape memory alloy rods

Large diameter rods of Cu-Al-Mn shape memory alloy were gas tungsten arc welded. The microstructural evolution was studied by electron microscopy techniques and its impact on the mechanical and functional response of the welded joints was assessed. The fusion zone exhibited a mixture of α and β phases, while the base material was composed only by the parent β phase. The refined grain structure of the fusion zone increased the material ductility and can improve the functional fatigue resistance of the welded joint when compared to the original base material.

Experimental study on self-centering link beams using post-tensioned steel-SMA composite tendons

Compared with conventional steel link beams, which undergo unrecoverable plastic deformation during earthquake, the self-centering link beams exhibit recoverable deformation under seismic load. This paper illustrates a new concept of self-centering link beam system which uses post-tensioned composite tendons consisting of steel rods and shape memory alloy rods to provide re-centering force and energy dissipation capacity. A pseudo-static experiment was conducted to testify the feasibility of this novel self-centering system. The experimental results showed that the self-centering link beam system using composite tendons was able to re-center from the designed rotation of 8% rad with a negligible residual deformation and a medium energy dissipation capacity, and possessed an over-strength factor comparable to conventional systems. A numerical simulation on the experiment was carried out to cross-validate the experimental results. Comparison between the numerical results and experimental results showed they were generally consistent with each other.

Large Dimension and Low-Cost Fe-SMA Rods

The effects on sample size on abnormal grain growth in inexpensive FeMnAlNi shape memory alloy (SMAs) wires and rod were investigated. It was shown that repeated heat treatments between single phase (bcc) and two phase (bcc + fcc) region resulted in abnormal grains with bamboo structure both in small sized wires and large diameter rods. Microstructural features were investigated using electron backscatter diffraction (EBSD) and it was found that 0.5 mm wires possess strong [011] texture whereas, large diameter rods have random texture after grain growth heat treatments.