Shape Memory Alloy Wires Research Articles

Performance analysis of position sensorless control of antagonistic shape memory alloy actuators

Abstract This paper presents a comprehensive performance analysis of position sensorless control of antagonistic shape memory alloy actuators (ASMAA), focusing on enhancing the sensorless position sensing capabilities and servo performance. The mechanisms and influencing factors of ASMAA self-sensing characteristics are comprehensively analyzed. A self-sensing model framework based on the constitutive model of ASMAA is proposed, and a self-sensing model based on differential resistance feedback is developed. An experimental platform based on the ASMAA motion mechanism is established to test and analyze SMA wires of two different materials under various pretension force conditions. The experimental results show that the antagonistic configuration mitigates hysteresis and improves linearity. A simple polynomial fitting is employed to establish the resistance-displacement relationship, achieving good accuracy with minimal residuals. The system identification is employed to avoid the parameter complexity and time-varying in the constitutive model. Based on the identified transfer function, a traditional PID controller is designed for position sensorless servo control. However, the inherent nonlinear hysteresis of ASMAA is difficult to suppress using a linear PID controller. Furthermore, a compound control strategy based on the Duhem model and PID controller is proposed, which utilizes the particle swarm optimization (PSO) algorithm to identify the Duhem inverse model controller. Experimental results demonstrate that the compound controller significantly enhances position tracking accuracy and response speed compared to a standalone PID controller.

The synergistic effect of nano-Al2O3 size and concentration on the interfacial adhesion properties of SMA/PDMS composites and their enhancement mechanism

Soft actuators composed of shape memory alloy (SMA) wires embedded in polydimethylsiloxane (PDMS) matrix hold potential for shape-morphing structures and soft robots. However, SMA exhibits poor bonding with PDMS due to its smooth and nonpolar surfaces. Nanoparticles show promise in interfacial strengthening of polymer composites. In this work, KH590 was used to modify nano-Al2O3 particles and deposited on the SMA surface, creating a three-dimensional nanostructure bridging SMA and PDMS to enhance interface strength. The synergistic effects of particle size and content of nano-Al2O3 particles on the interface strength were investigated in detail. It founds that interfacial strength decreased exponentially with particle size at content of 1 wt%, while when the content exceeds 1 wt%, the interface strength firstly increases with the particle size and then decreases in a logarithmic trend. Specifically, the interface strength is enhanced by 110 % with 3 wt% 50 nm particles. The interface enhancement mechanism was also discussed. The proposed nanoparticle modification approach was to strengthen SMA/PDMS interphase by increasing and extending fracture path, consuming more fracture energy. Chemical cross-linking also contributed to interface enhancement. This work enhances understanding of interfacial bonding mechanisms and provides valuable guide for interfacial strengthening of SMA/PDMS.

Cyclic functional degradation of NiTi shape memory alloy wires in wide ranges of strain rate and ambient temperature

Shape memory alloy (SMA) dampers frequently experience cyclic loading over a broad spectrum of strain rates and ambient temperatures, resulting in a significant thermo-mechanical coupling effect during cyclic deformation. Nevertheless, the impact of this coupling effect on the functional degradation of SMAs has not been thoroughly examined, particularly in scenarios involving severe deformation. In this study, a series of strain-controlled cyclic loading–unloading tests were conducted on NiTi SMA wires utilizing various combinations of strain rates ranging from 5 × 10−4 6 × 10−2/s and different ambient temperatures (313–393 K). The functional degradation was exacerbated by increasing ambient temperature and loading rate due to the complex interactions among the inelastic deformation mechanisms and thermo-mechanical coupling effects. Furthermore, although the cyclic deformation behavior of NiTi SMA wires varied with the loading rate, this rate dependence diminished with increasing ambient temperature. The synergistic effect of elevated strain rates and high temperatures markedly accelerated the fatigue failure of NiTi SMA wires and substantially altered the underlying microstructural morphology. These findings can provide valuable support for evaluating the service performance of NiTi SMA dampers under various engineering conditions and contribute to developing a cyclic constitutive model for NiTi SMAs.

A new concept of structural smart fabric activated by shape memory alloys

Abstract This work presents the development, prototyping and validation of a new concept of structure called Structural Smart Fabric (SSF). An SSF is a chainmail fabric composed by interconnected elements, called cells, which can be stiffened by reactive elements, such as those made by Shape Memory Alloy (SMA). Exploiting the shape memory functionality, SSFs are capable of sensing and reacting to external stimuli. Based on this concept, in this study we propose an SSF that integrates SMA wires into a 3D-printed chainmail structure. The shape memory effect of these wires is used as an actuating mechanism that, at high temperature, tightens the adjacent cells together and provides increased structural stiffness. In this study, finite element simulations were initially conducted to enhance the comprehension of the SSF’s mechanical behaviour. The influence of the initial cell spacing on the SSF stiffness and the wire stress profiles was evaluated during bending loading, as well as the evolution of contact pressure profiles between adjacent cells. This numerical approach enabled to tune the design of the SSF prototypes which were successively manufactured using Selective Laser Sintering (SLS) additive manufacturing technology with PA12. After the integration with the SMA wires, the SSF prototypes were tested under a 3-point bending configuration at different temperatures. The results revealed a remarkable increase in structural stiffness at elevated temperatures compared to ambient conditions. This study set the basis for a deeper understanding of SSF's unique capabilities and potential applications in fields where adaptive and responsive structures are required.

Wearable Haptics for Orthotropic Actuation Based on Perpendicularly Nested Auxetic SMA Knotting.

Smart wearable tactile systems, designed to deliver different types of touch feedback on human skin, can significantly improve engagement through diverse actuation patterns in virtual or augmented reality environments. Here, a perpendicularly nested auxetic wearable haptic interface is reported for orthotropically decoupled multimodal actuation (WHOA), capable of producing diverse tactile feedback modes with 3D sensory perception. WHOA incorporates shape memory alloy wires that are intricately knotted into an auxetic structure oriented along orthotropic dual axes. Its perpendicularly nested auxetic structure enables orthotropic actuation, allowing independent expansion and contraction along both x and y-axes, as confirmed by force-strain and displacement-time performance tests. Additionally, the perylene coating provides orthogonal electrical isolation to WHOA, allowing for stripe-specific localized actuation and enabling multiple tactile feedback modes. As an orthotropic wearable haptic interface, WHOA distinguishes between x-axis and y-axis directions and ultimately delivers multi-dimensional information regarding movements in 3D space through tactile feedback. As a result, when worn on the foot or arm, WHOA naturally delivers spatiotemporal tactile information to the user, facilitating navigation and teleoperation with 3D sensory perception.

Morphing flap driven by link with antagonistic shape memory alloy wires

Abstract This paper describes a study of a morphing flap using antagonistically arranged shape memory alloy (SMA) wires as actuators. The main focus of this study is to examine how existing aircraft structures and mechanisms can be modified to make the morphing airfoil more practical. The first step is to consider the drawbacks of existing morphing airfoils and then examine the advantages of the morphing airfoil proposed in this study. Then, a morphing airfoil is proposed to realize four significant technical issues: weight reduction, compatibility with existing structures, securing internal space, and seamless skin made with shape memory polymer (SMP) films. First, elemental experiments were conducted to examine the feasibility of the mechanical design, and the feasibility of the design of a large-morphing airfoil operating test model was confirmed. Next, aerodynamic and structural-mechanical analyses are conducted while designing the experimental operating model to verify whether it could operate up to the target flap angle under simulated flight conditions. After completing the experimental model, actuation tests are conducted as a morphing wing and confirm whether the wing could operate at the target flap angle in a realistic environment. As a result, the two-way morphing flap angle was experimentally observed. It is noted that only aerodynamic force was not considered in the experiment, which is further investigated in wind tunnel tests in future study. In addition, control rate of the proposed system seems improved than conventional model because of the reduction of the wire length of the actuation system. Thus, the results obtained in this study suggested the proposed link-driven SMA wire mechanism can be applied to make the morphing airfoil more practical.

Shape control of an adaptive 3D-printed beam with integrated FBG sensors and SMA wires: modeling and experimental testing

Shape control of an adaptive 3D-printed beam with integrated FBG sensors and SMA wires: modeling and experimental testing

Effect of Hydrogen on the Transformation Ratcheting of NiTi SMA Wires: Experiment and Modeling

Effect of Hydrogen on the Transformation Ratcheting of NiTi SMA Wires: Experiment and Modeling

LSTM-Based Self-Sensing Application of Shape Memory Alloy Wire Actuators Under Practical Loading Conditions

LSTM-Based Self-Sensing Application of Shape Memory Alloy Wire Actuators Under Practical Loading Conditions

Dissimilar Resistance Welding of NiTi Microwires for High-Performance SMA Bundle Actuators

Shape memory alloys (SMAs) are becoming a more important factor in actuation technology. Due to their unique features, they have the potential to save weight and installation space as well as reduce energy consumption. The system integration of the generally small-diameter NiTi wires is an important cornerstone for the emerging technology. Crimping, a common method for the mechanical and electrical connection of SMA wires, has several drawbacks when it comes to miniaturization and high-force outputs. For high-force applications, for example, multiple SMA wires in parallel are needed to keep actuation frequencies high while scaling up the actuation force. To meet these challenges, the proposed study deals with the development of a resistance-welding process for manufacturing NiTi wire bundles. The wires are welded to a sheet metal substrate, resulting in promising functional properties and high joint strengths. The welding process benefits from low costs, easy-to-control parameters and good automation potential. A method for evaluating the resistance-welding process parameters is presented. With these parameters in place, a manufacturing process for bundled wire actuators is discussed and implemented. The welded joints are examined by peel tests, microscopy and fatigue experiments. The performance of the manufactured bundle actuators is demonstrated by comparison to a single wire with the same accumulated cross-sectional area.

Martensitic transformation induced by cooling NiTi wire under various tensile stresses: Martensite variant microstructures, textures, recoverable strains and plastic strains

Whenever the forward and/or reverse B2 cubic to B19’ monoclinic martensitic transformation in NiTi shape memory alloy wire proceeds under external stress above certain threshold, it generates incremental plastic strains which accumulate during thermomechanical cyclic loading and lead to functional fatigue preventing many promising engineering applications from realization. In this work, unique thermomechanical loading experiments were performed on NiTi shape memory wire with the aim to reveal the mechanism by which the forward martensitic transformation upon cooling under external stress generates plastic strain. Recoverable transformation strains and plastic strains generated by the forward transformation on cooling under various tensile stresses were evaluated, martensite variant microstructures in grains were reconstructed by nanoscale orientation mapping in TEM, martensite textures after cooling at room temperature were evaluated by in-situ synchrotron x-ray diffraction and permanent dislocation defects in martensite were analyzed by TEM. Based on the obtained experimental evidence, it is proposed that the forward martensitic transformation on cooling under stress proceeds via habit plane interfaces between austenite and second order laminate of (001) compound twins in martensite. Depending on the magnitude of the applied stress, the induced martensite reorients, partially detwins and deforms plastically via [100](001) dislocation slip in martensite in extent permitted by the requirement for compatible deformation of grains in nanocrystalline NiTi wire via a single deformation system. During the forward MT upon cooling under highest stresses 600 MPa, the martensite deforms via kwinking deformation enabling generation of large plastic strains 8 %.

Deflection and Performance Analysis of Shape Memory Alloy-Driven Fiber–Elastomer Composites with Anisotropic Structure

Due to their advantageous characteristics, shape memory alloys (SMAs) are prominent representatives in smart materials. They can be used in application fields such as soft robotics, biomimetics, and medicine. Within this work, a fiber–elastomer composite with integrated SMA wire is developed and investigated. Bending and torsion occur when the SMA is activated because of the anisotropic structure of the textile. The metrological challenge in characterizing actuators that perform both bending and torsion lies in the large active deformation of the composite and the associated difficulties in fully imaging and analyzing this with optical measurement methods. In this work, a multi-sensor camera system with up to four pairs of cameras connected in parallel is used. The structure to be characterized is recorded from all sides to evaluate the movement in three-dimensional space. The energy input and the time required for an even deflection of the actuator are investigated experimentally. Here, the activation parameters for the practical energy input required for long life with good deflection, i.e., good efficiency, were analyzed. Different parameters and times are considered to minimize the energy input and, thus, to prevent possible overheating and damage to the wire. Thermography is used to evaluate the heating of the SMA wire at different actuation times over a defined time.

Data‐driven simulation of functional fatigue in shape memory alloy wires

AbstractData‐driven mechanics offers great potential in engineering applications, where the efficient simulation of complex and, in particular, path‐dependent material behavior is often challenging. Within this approach, conventional material models are replaced by data sets containing snapshots of stress, strain and the history of both assumed to be sufficiently accurate representations of the underlying material behavior. Based on these snapshots and on physical admissibility, a distance function is built which is minimized to yield the boundary value problems' solution. The aim of this paper is to apply this framework to accurately simulate the complex behavior of shape memory alloy wires under cyclic loading, under which these materials exhibit a degradation of their features, denoted functional fatigue. The constructed synthetic data sets are enriched by real experimental data, showcasing that the data‐driven method is capable of combining both approaches of classic material modeling and modern methods which directly incorporate experimental data.

Development of Lightweight 6 m Deployable Mesh Reflector Antenna Mechanisms Based on a Superelastic Shape Memory Alloy

This paper describes the design and experimental verification of a 6 m parabolic deployable mesh reflector antenna mechanism based on a superelastic shape memory alloy. This antenna mainly consists of a deployable primary reflector with a superelastic shape memory alloy-based hinge mechanism and a fixed-type secondary reflector mast, where a rotary-type holding and release mechanism and deployment speed control system are installed. The main feature of this antenna is the application of a superelastic shape memory alloy to the mechanism, which has the advantages of plastic deformation resistance, high damping, and fatigue resistance. A shape memory alloy is applied to the hinge mechanism of each primary reflector rib and to the rotary-type holding and release mechanism as a deployment mechanism. In addition, a superelastic shape memory alloy wire is applied to the antenna in the circumferential direction to maintain the curvature of the primary reflector. The effectiveness of the proposed mechanism design was verified through repeated deployment tests on models of the superelastic shape memory alloy-based hinge mechanism and the antenna system.

Dynamic characteristics and vibration control of composite laminate wall panels in electric aircraft using NiTi shape memory alloys

This paper investigates the dynamic characteristics and vibration control of a new-energy electric aircraft cockpit wall panel. An innovative boundary-splitting Rayleigh-Ritz method is introduced for modal analyses of wall panel structures in thermal environments, verified with the hammering and finite element methods, showing a maximum error of 5.42 %. NiTi shape memory alloy (SMA) wires are embedded in composite structures for vibration control, with the first theoretical-experimental validation performed. A parametric fitting-computational model for NiTi-SMA is developed to extract mechanical parameters from hysteresis data. Theoretical models are decoupled into dynamical equations using the Galerkin truncation method. The damping capability of NiTi-SMA is demonstrated by solving the amplitude using the harmonic balance and Runge-Kutta methods. Room-temperature and variable-temperature vibration tests show over 30 % vibration control capability with optimized embedding methods. These experimental results confirm the theoretical findings, providing support for the analysis and vibration control of new-energy aircraft.

Proof of Concept of a New Revision Procedure for Ceramic Inlays of Acetabular Cups Using a Shape-Memory Alloy Actuator System.

The revision of ceramic inlays of acetabular cups is a challenging surgical procedure. The mechanical impact during the inlay extraction process can damage the ceramic or metal cup rim. To avoid these risks, a concept for a new revision procedure was developed. It is based on an actuator system, which allows a non-destructive release of the ceramic inlay. To integrate the actuator system, different design concepts of acetabular cup components were investigated, and an actuator based on shape-memory alloy (SMA) wires was developed. The process chain for the actuator, starting from nickel-titanium wires manufactured into the actuator geometry by laser welding and thermo-mechanical treatment for the shape setting process up to the functionality evaluation of the actuator system, was implemented on a laboratory scale. The new revision procedure is based on a phase transformation of the SMA wire actuator, which was obtained through two methods-applying an electrical current by an instrument and rinsing the wire with heated water. The phase transformation of the actuator resulted in a contraction between 3.2% and 4.3% compared to its length after pre-stretching and was able to release the ceramic inlay from the cup. Therefore, the developed actuator design and process chain is a proof of concept towards a new revision procedure for modular acetabular cups.

Enhanced interface adhesion in shape memory alloy hybrid composites via an elastomeric interface: An experimental and numerical investigation

Shape Memory Alloy Hybrid Composites (SMAHCs) hold great promise for different applications. However, the interface between SMAs and the matrix presents challenges due to large strains associated with the martensitic transformations (MTs). Although different strategies have been proven effective in increasing interfacial strength, debonding and its prevention remain unresolved. Therefore, to enable MTs in SMAHCs, this paper proposes a novel solution using a rubber-like elastomeric interface. Pull-out SMAHC specimens were tested at different embedding lengths with and without the elastomeric interface. Specimens with the elastomeric interface showed better performance and stress-strain transfer during MT up to SMA wire breakage. The behaviour of the interface was studied using finite element analysis. A fine-tuning method was proposed for the cohesive zone model parameters. Simulated pull-out tests matched experimental data, revealing the debonding mechanisms. However, results with the elastomer underscored the need to fully represent the underlying physics of the highly deformable interface.

Soft Crawling Microrobot Based on Flexible Optoelectronics Enabling Autonomous Phototaxis in Terrestrial and Aquatic Environments.

Many organisms move directly toward light for prey hunting or navigation, which is called phototaxis. Mimicking this behavior in robots is crucially important in the energy industry and environmental exploration. However, the phototaxis robots with rigid bodies and sensors still face challenges in adapting to unstructured environments, and the soft phototaxis robots often have high requirements for light sources with limited locomotion performance. Here, we report a 3.5 g soft microrobot that can perceive the azimuth angle of light sources and exhibit rapid phototaxis locomotion autonomously enabled by three-dimensional flexible optoelectronics and compliant shape memory alloy (SMA) actuators. The optoelectronics is assembled from a planar patterned flexible circuit with miniature photodetectors, introducing the self-occlusion to light, resulting in high sensing ability (error < 3.5°) compared with the planar counterpart. The actuator produces a straightening motion driven by an SMA wire and is then returned to a curled shape by a prestretched elastomer layer. The actuator exhibits rapid actuation within 0.1 s, a significant degree of deformation (curvature change of ∼87 m-1) and a blocking force of ∼0.4 N, which is 68 times its own weight. Finally, we demonstrated the robot is capable of autonomously crawling toward a moving light source in a hybrid aquatic-terrestrial environment without human intervention. We envision that our microrobot could be widely used in autonomous light tracking applications.

Pulsed electric current annealing of (Ni,Cu)-rich Ti49Ni41Cu10 shape memory wire for superior superelasticity and stable elastocaloric cooling effect

This study designed a (Ni,Cu)-rich Ti49Ni41Cu10 shape memory wire annealed by pulsed electric treatment of 60 A/mm2 for 0.3 sec. Granular and strip-type Ti(Ni,Cu)2 precipitates, formed before application of the electric current treatment, facilitated the plastic deformation during the wire drawing process. The wire demonstrated stability in superelasticity and elastocaloric cooling capability. The accumulated residual strain was only 0.15 % after 50 superelastic cycles with an applied strain of 3.5 % at 338 K. The elastocaloric temperature drop of the wire remained at about 9.4 K for 50 cycles. Moreover, under 3 % applied strain, the wire exhibited elastocaloric temperature drops of 5.3 K to 8.1 K within the application window of 323 K to 373 K. TEM observations confirmed that the grain size of the wire was about 20–30 nm, which led to the homogeneous superelasticity performance. Furthermore, the superior compatibility between the B2 and B19 phases reduced plastic deformation at the interfaces during martensitic transformation. The stable functionality and elastocaloric cooling capacity of the wire originated from the combination of nanocrystalline structure and superior compatibility between the B2 and B19 phases. These results demonstrated that the Ti49Ni41Cu10 SMA wire could be fabricated due to the presence of ductile Ti(Ni,Cu)2 precipitates, and the subsequent pulsed electric current treatment caused rapid annealing to achieve a stable functional performance.

Enhancing non-metallic gasket performance with shape memory fibers

This study aims to enhance the sealing performance of non-metallic gaskets by incorporating shape memory fibers. The analytical exploration focuses on analyzing the thermomechanical behavior of Nitinol fibers in their woven state within the gasket. Specifically, the investigation examines the variation of phase transformation zones across the wire cross-section with changes in temperature. Subsequently, a series of SMA fiber-reinforced gasket samples were fabricated, and experimental investigations were conducted to assess the impact of Nitinol fibers on composite gaskets using a helium gas leak test. The results demonstrate that the integration of shape memory alloy wires into the composition of gaskets can significantly improve their sealing performance. Moreover, this study examines a number of pivotal factors such as fiber volume fraction, temperature application, woven fiber arrangement, leakage rates, gasket deformation, contact stress, and structural bending. These comprehensive investigations may provide valuable insights into the efficacy of Nitinol fibers in enhancing gasket sealing performance.