Shape Memory Alloy Wires Research Articles

On the Impact of γ´ Precipitates on the Transformation Temperatures in Fe–Ni–Co–Al–Ti–B Shape Memory Alloy Wires

On the Impact of γ´ Precipitates on the Transformation Temperatures in Fe–Ni–Co–Al–Ti–B Shape Memory Alloy Wires

Shaking table tests on seismic behaviors of a single-layer spherical lattice shell with shape memory alloy-controlled friction pendulum bearings

An innovative seismic isolation device incorporating a friction pendulum bearing (FPB) and vertically aligned shape memory alloy (SMA) strands is proposed for the seismic control of spherical lattice shells located in strong-earthquake regions. To validate the effectiveness of the proposed SMA-FPBs experimentally, a 1/10-scale single-layer spherical lattice shell test structure and a set of isolators were designed and fabricated. A shaking table was used to apply various three-dimensional seismic excitations to test structures equipped with and without different isolation bearings (SMA-FPBs or bare FPBs). Significant seismic behavior enhancements were observed when such isolation systems were used. However, bare FPBs cannot accommodate excessive displacements induced by high seismic intensities owing to their lack of adaptive control. In contrast, SMA-FPBs exhibited satisfactory control performance in terms of the peak and residual bearing displacements under fortification and rare seismic actions, and the adaptive properties of the SMA-FPBs protected the isolators from disassembly owing to excessive sliding displacements under extremely rare earthquakes, even though their re-centering abilities decreased slightly because of the failure of several SMA wires. Finally, the larger number of SMA wires in an SMA-FPB enhanced its restraining capacity against peak bearing displacement rather than improving the seismic responses of structural nodes and members.

A Novel Cooling Design for an Agonistic–Antagonistic SMA Tendon-Driven Actuator

Shape memory alloys (SMAs) exhibit a unique property that undergoes deformation in response to temperature variation. This characteristic can be utilized via the application of a filiform SMA wire to tendon-driven robotic actuators for biomimetic joint movements. However, due to the inefficiencies in heat dissipation, conventional SMA tendon-driven actuators are characterized by their lower relaxation speeds than other actuators. This paper proposes a novel cooling design for an SMA tendon-driven actuator using thin-fin heat sinks based on a multi-layer wrapped SMA tendon design. In addition, the electric circuit and the controller are refined. Prototype devices are constructed to validate the performance of SMA-based actuators under PID control. The results indicate that the proposed design exceeds previous models in terms of relaxation performance by up to 5.8 times while also being able to stabilize at a target angle within 0.5 s under control.

Development and evaluation of a light-weight flexure-based lockable joint for morphing wings

Single degree of freedom (single-DOF) morphing wings have the advantages of light-weight and multiple morphing shapes, which can enable aircraft to adapt to uncertain flight environments and various mission types. A single-DOF morphing wing with four morphing shapes designed based on the reconfigurable mechanism is introduced firstly in this paper. Then, a light-weight compliant locking mechanism (CLM) based on flexure hinges is proposed for lockable joints in the reconfigurable mechanism. The CLM has two types depending on the locking method, namely the “plug-in” compliant locking mechanism (PCLM) and the “friction” compliant locking mechanism (FCLM). The working principles of the two CLMs are described. The mathematical models are established to assess the static and dynamic characteristics of the proposed CLM, which are also verified by the finite element simulation. The influence of the flexure hinge dimensions on the working performance of the CLM is analyzed, and its dimensions are optimized considering both the locking performance and the maximum stress. Finally, a PCLM and a FCLM actuated by SMA wires are fabricated based on the optimized dimensions. The experiment is conducted to assess the locking torque of the CLM and the feasibility of the proposed CLM used for morphing wings is confirmed.

Fully coupled electric-thermo-mechanical model for predicting the response of a SMA wire activated by electrical input

Fully coupled electric-thermo-mechanical model for predicting the response of a SMA wire activated by electrical input

Novel design and fabrication of a linear actuator based on shape memory alloy wire winding in hexagonal architecture

Novel design and fabrication of a linear actuator based on shape memory alloy wire winding in hexagonal architecture

Largely deformable torsional soft morphing actuator created by twisted shape memory alloy wire and its application to a soft morphing wing

We present a new type of torsional soft morphing actuator designed and fabricated by twisted shape memory alloy (SMA) wires embedded in polydimethylsiloxane matrix. The design and fabrication process of the proposed soft morphing actuator are presented with investigations of its working mechanism. Actuation performance was evaluated with respect to the temporal response, the maximum torsional deformation under an applied electric current, and various design parameters including the twist direction, wire diameter, helical pitch of the SMA wire, and the actuator’s thickness and length. We demonstrate potential applications of the proposed soft morphing actuator as a soft morphing wing and airfoil. The proposed actuator will aid in the development of soft actuators, soft robotics, and other relevant scientific and engineering applications.

Synthesis of a Bistable Recuperative Pump Powered by Shape Memory Alloys and a Two-Section Involute Cam

The paper discusses the synthesis problem of a bistable piston pump, employing a driving mechanism that comprises shape memory alloy wires, a two-section involute cam, and an energy-recuperating spring. The transition from one stable end position to another in the pump is achieved by heating and subsequently shortening one of the shape memory alloy wires, initiating the motion of the mechanism. This is then followed by the engagement of the recuperative spring to traverse the intermediate unstable equilibrium position and complete the entire stroke. The reversal of motion follows a similar approach, where the second SMA wire shortens while the first wire remains in a cold state. Importantly, the mechanism necessitates a low force within the shape memory alloy wire to initiate motion towards the opposite stable position. This research encompasses the examination of type, geometric, and force synthesis considerations for the pump, leading to the development of fundamental kinematic and force relationships. Moreover, a novel mechanism is proposed and synthesized, incorporating a two-section involute cam with a cusp point, to generate the desired discontinuous moment function produced by the recuperative spring. Further analysis reveals that the thermal time constant, which regulates the dynamic response of the mechanism, is directly proportional to the diameter of the driving SMA and inversely proportional to the square root of the number of SMA branches.

New phase diagram for low hysteresis response of a coiled shape memory alloy actuator

We demonstrate a new phase diagram describing the responses of shape memory alloy (SMA) spring actuators. The SMA spring actuator has a wide range of temperatures for phase transitions and responses with low hysteresis. To describe these specific responses of the SMA spring actuator, a new phase diagram with an overlapping layer is proposed. In the overlapping layer, even if it changes from a heating phase to a cooling phase or vice versa, a phase transition occurs whenever the temperature of the SMA changes. Because there is no region in which only the temperature changes without a force changes, the hysteresis is reduced. The overlapping layer is formed by changing the properties of the SMA when fabricating the spring actuator. One of the properties that change in the SMA is the amount of latent heat when the phase transition occurs. The latent heat of the SMA spring is significantly low compared to that of the SMA wire due to the plasticity produced by the stress applied to form the spring shape. Therefore, there will be a tradeoff between the amount of the phase transition and the hysteresis of the SMA actuator.

Easy-To-Wear Auxetic SMA Knot-Architecture for Spatiotemporal and Multimodal Haptic Feedbacks.

Wearable haptic interfaces prioritize user comfort, but also value the ability to provide diverse feedback patterns for immersive interactions with the virtual or augmented reality. Here, to provide both comfort and diverse tactile feedback, an easy-to-wear and multimodal wearable haptic auxetic fabric (WHAF) is prepared by knotting shape-memory alloy wires into an auxetic-structured fabric. This unique meta-design allows the WHAF to completely expand and contract in 3D, providing superior size-fitting and shape-fitting capabilities. Additionally, a microscale thin layer of Parylene is coated on the surface to create electrically separated zones within the WHAF, featuring zone-specified actuation for conveying diverse spatiotemporal information to users with using the WHAF alone. Depending on the body part it is worn on, the WHAF conveys either cutaneous or kinesthetic feedback, thus, working as a multimodal wearable haptic interface. As a result, when worn on the forearm, the WHAF intuitively provides spatiotemporal information to users during hands-free navigation and teleoperation in virtual reality, and when worn on the elbow, the WHAF guides users to reach the desired elbow flexion, like a personal exercise advisor.

A Physics-Based Hybrid Dynamical Model of Hysteresis in Polycrystalline Shape Memory Alloy Wire Transducers

Shape memory alloys (SMAs) are a class of smart materials that exhibit a macroscopic contraction of up to 5% when heated via an electric current. This effect can be exploited for the development of novel unconventional actuators. Despite having many features such as compactness, lightweight, and high energy density, commercial SMA wires are characterized by a highly nonlinear behavior, which manifests itself as a load-, temperature-, and rate-dependent hysteresis exhibiting a complex shape and minor loops. Accurate modeling and compensation of such hysteresis are fundamental for the development of high-performance SMA applications. In this work, we propose a new dynamical model to describe the complex hysteresis of polycrystalline SMA wires. The approach is based on a reformulation of the Müller–Achenbach–Seelecke model for uniaxial SMA wires within a hybrid dynamical framework. In this way, we can significantly reduce the numerical complexity and computation time without losing accuracy and physical interpretability. After describing the model, an extensive experimental validation campaign is carried out on a 75- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m diameter SMA wire specimen. The new hybrid model will pave the development of hybrid controllers and observers for SMA actuators.

Advanced additive manufacturing of self-healing composites: Exploiting shape memory alloys for autonomous restoration under mixed-mode loading

Applying Additive Manufacturing (AM) techniques has facilitated the production of innovative self-healing structures that can acclimate to environmental fluctuations by considering their damage response. This paper introduces a novel approach for fabricating AM composites reinforced with Shape Memory Alloys (SMAs) and possessing self-healing capabilities. The self-healing performance of the composites is assessed by subjecting undamaged and repaired samples to mixed mode I/II loading conditions using pre-cracked Semi-Circular Bending (SCB) specimens. Supplementary parameters that impact the self-healing process, including varied pre-strain levels of 1%, 2%, and 4.3% for SMA wires, are investigated. The outcomes of these pre-strain levels are subsequently compared to the repair scenario in the absence of SMAs. The transferred healing agent volume to the damaged region and the remaining crack opening is quantified using a thermography camera and image processing techniques. The study’s results demonstrate that self-healing can be achieved through strategic considerations of pre-strain levels in SMA strings and loading modes. Furthermore, the study suggests that neglecting such concerns may potentially have deleterious effects on layered samples' load-bearing capacity. The proposed methodology holds great promise for producing self-healing 3D-printed composite specimens in the laboratory and scaling them up to real-world applications.

A Machine Learning Empowered Shape Memory Alloy Gripper With Displacement-Force-Stiffness Self-Sensing

This paper proposes a multiple self-sensing gripper (MssGripper) driven by the shape memory alloy (SMA) and empowered by machine learning algorithms. The MssGripper can identify objects without external sensors. A single SMA wire can drive the gripper for self-sensing accurately. This paper confirms the resistance of the SMA can reflect the phase transition and can be used for displacement and force prediction, as well as for object stiffness prediction. Through machine learning, a backpropagation neural network (BPNN) and long-short-term-memory (LSTM) are used to establish multiple self-sensing models for prediction. The robustness experimental results show that the self-sensing models based on LSTM have higher prediction accuracy. The average root-mean-square errors of displacement prediction and force prediction are 0.063 mm and 0.236 N, respectively, and the stiffness prediction error is less than 9.4%. Moreover, the accuracy of the classifier in stiffness identification is 97.2%. The MssGripper can accurately predict the displacement, force, and stiffness and identify objects such as springs, rubber bars and steel bars. The establishment of the models expands the novel idea of gripper sensing, which is beneficial to promoting miniaturization and compactness.

Mechanisms boosting material embodied intelligence to realize self-healing soft robots

The recent introduction of self-healing soft materials in robotics is a major step towards sustainable next generation robots. By manufacturing soft robots out of these smart materials, we integrate a self-healing ability and increase the physical intelligence of these systems. However, the embodied intelligence in the material level needs to be augmented by incorporating assistive mechanisms in the system level with minimized control, enabling healing of damage in different sizes and in diverse working conditions. These assistive mechanisms can provide damage detection, damage closure, healing stimuli providing, health monitoring, or a combination of the previous. In this paper, we present two different mechanisms for an autonomous healing of damages; (i) Embedding a healable heater in a self-healing soft actuator to increase the temperature required for an efficient healing, while it allows detecting the damage and monitoring the health of the system. (ii) Incorporating shape memory alloy wires in a self-heling soft bending actuator, with simultaneous sealing through contraction and heating abilities. Apart from assisting in the healing action, both mechanisms play a part in the actuation of the bending robots as strain limiting elements. These assistive mechanisms will overcome the limitation on the material level, leading to robots that can self-heal in applications outside of laboratories and factories.

A bidirectional rotating actuator by using a single shape memory alloy wire in a double bend shape

A bidirectional rotating actuator by using a single shape memory alloy wire in a double bend shape

Post-buckling and vibration analysis of double-curved sandwich panels with SMA embedded faces

Shape memory alloys, especially in the form of wire, can provide structures with magnificent improvements in buckling and frequency responses. The SMA's ability to recover its original shape can produce a sizable amount of recovery stress, resulting in enhancing natural frequency and critical temperature and lowering the maximum deflection of structures. In this study, in addition to considering the effects of SMA presence in double-curved sandwich plate on the aforementioned characteristics, the influences of heat treatment of curing SMAs on their properties, calculated by differential scanning calorimetry (DSC) and tensile testing, and sandwich structures will be considered. Furthermore, the effects of recovery stress, the volume fraction, and the position of SMA wires on thermal and mechanical stability will be studied. The Boyd & Lagoudas SMA constitutive model is utilized in the ABAQUS UMAT subroutine.

Seismic risk-based optimization of tension-only shape-memory alloy device for steel moment-resisting frames

This study introduces the seismic risk-based design of SMA devices for steel moment-resisting frame buildings. The investigation begins with the numerical representation of the device which includes SMA wires exhibiting super-elastic stress–strain response, along with steel components. The model is then compared against an actual test result. Accordingly, several four-story steel-frame buildings are numerically characterized, all designed to withstand similar seismic loads. This includes a control frame building (Bare-SMF), a frame building with SMA devices using a traditional design approach (SMA-D), and a frame with buckling restrained braces (BRB-D) for comparison. As the traditional design method relies on the first modal shape and static loads, the pushover analysis results for all structures possessed similar amount of strength and deformation capacity. However, the nonlinear time history analysis revealed inconsistencies in the responses of the retrofitted buildings (SMA-D and BRB-D) when compared to Bare-SMF. To address this issue, a seismic risk-based design approach that combines nonlinear time history analysis on a steel moment-resisting frame and the particle swarm optimization algorithm is employed. By using this approach, the SMA brace quantities were determined such that the cost of SMA devices can be minimized while the life-cycle probability of collapse and demolition is smaller than that of Bare-SMF. As a result of the risk-based design approach, three brace quantities are determined according to a decision maker’s attitude against the seismic risk. As a result, the cost of SMA devices could be reduced by more than 40% while maintaining a significant reduction in the life-cycle probability of collapse and demolition.

Effect of polyurethane coating on mechanical response of shape memory alloy wires

In micro-electro-mechanical systems, the risk of short circuit arises when shape memory alloy (SMA) wire actuators mistakenly come into contact with other metal parts. Coating the SMAs with insulating layer can solve this problem. However, unlike traditional conductive wires that experience minimal length changes with current, SMA wires undergo significant length variations during electrical execution. This can affect the bonding between the coating and the SMA wires, as well as the mechanical response of the actuators. Therefore, this study investigated the effect of an insulating coating on the mechanical response of SMA wires. The results show that a layer of polyurethane coating provides long-term insulation to the SMA wires. While this coating reduces the recoverable strain of SMA wires under passive heating, its effect on actuation strain under electrical heating is relatively minor. Additionally, the coating enables the SMA wire to work smoothly by relieving overshooting and vibration phenomena during execution, and helps the wire work in a wider current range than an uncoated wire. Moreover, the coating enhances the response speed of SMA wires during power-on but reduces the response speed during power-off, this influence weakens as driving currents increase. These distinct mechanical responses can be primarily attributed to the coating’s influence on heat transfer behavior of the SMA wires.

Novel self-centering cold-formed steel composite wall: Concept, theoretical analysis, and numerical investigation

Cold-formed steel (CFS) structures exhibit considerable superiority in efficient and environmentally friendly building construction in high-seismic regions. The objective of this study is to develop and validate the concept of self-centering cold-formed steel composite (SC-CFSC) wall structures, and to characterize the lateral behavior of an SC-CFSC wall through numerical and theoretical analyses. Based on tests on shape memory alloy wires and CFSC walls, their hysteretic behavior is applied in ABAQUS to construct a finite element (FE) model of an SC-CFSC wall. The FE and theoretical analysis results of the SC-CFSC wall are in reasonable agreement, and valuable information regarding the design of the SC-CFSC wall is summarized. This study not only aims to provide a novel concept of self-centering CFS structures, but also to provide comprehensive explanation regarding the theoretical derivation and simulation procedures for characterizing the lateral behavior of both CFSC and SC-CFSC walls.

Design and Characteristics of Shape Memory Alloy Bidirectional Torsional Actuator

To overcome the problems of the low power/weight ratio of traditional servo motors, complex transmission systems, and large space occupied by hydraulic drive systems, this paper designs a bidirectional torsional actuator using the shape memory effect of Ti-Ni shape memory alloy (SMA) wire, which aims to realize the folding and unfolding of the wings of flying cars. The model of the designed actuator was established and the theoretical calculation was analyzed, based on which the experimental verification was carried out. It is found that when the heating current is 1.6 A, the mechanism can take into account the economy under the premise of meeting a certain folding speed. When the pre-stretching amount of SMA wire is 3%, the residual strain corresponding to the wire is small, about 0.577%, and it can provide driving torque and torsion angle to meet the design requirements of the actuator. This verifies the feasibility of the actuator and obtains the driving characteristics of the actuator. Finally, the shortcomings and improvement measures of the actuator are analyzed briefly.