Shape Memory Wires Research Articles

Numerical and Experimental Study of a Wearable Exo-Glove for Telerehabilitation Application Using Shape Memory Alloy Actuators

Hand paralysis, caused by conditions such as spinal cord injuries, strokes, and arthritis, significantly hinders daily activities. Wearable exo-gloves and telerehabilitation offer effective hand training solutions to aid the recovery process. This study presents the development of lightweight wearable exo-gloves designed for finger telerehabilitation. The prototype uses NiTi shape memory alloy (SMA) actuators to control five fingers. Specialized end effectors target the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints, mimicking human finger tendon actions. A variable structure controller, managed through a web-based Human–Machine Interface (HMI), allows remote adjustments. Thermal behavior, dynamics, and overall performance were modeled in MATLAB Simulink, with experimental validation confirming the model’s efficacy. The phase transformation characteristics of NiTi shape memory wire were studied using the Souza–Auricchio model within COMSOL Multiphysics 6.2 software. Comparing the simulation to trial data showed an average error of 2.76°. The range of motion for the MCP, PIP, and DIP joints was 21°, 65°, and 60.3°, respectively. Additionally, a minimum torque of 0.2 Nm at each finger joint was observed, which is sufficient to overcome resistance and meet the torque requirements. Results demonstrate that integrating SMA actuators with telerehabilitation addresses the need for compact and efficient wearable devices, potentially improving patient outcomes through remote therapy.

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 %.

Influence of the insertion of shape memory wires in composite materials on impact response

Influence of the insertion of shape memory wires in composite materials on impact response

Designing a Robotic Gripper Based on the Actuating Capacity of NiTi-Based Shape Memory Wires

Designing a Robotic Gripper Based on the Actuating Capacity of NiTi-Based Shape Memory Wires

Stress induced martensitic transformation in NiTi at elevated temperatures: Martensite variant microstructures, recoverable strains and plastic strains

To shed light on the origin of the loss of functional properties of NiTi with temperature increasing above 100 °C, we have investigated stress induced martensitic transformations in nanocrystalline NiTi shape memory wire by thermomechanical tensile testing supplemented with post-mortem reconstruction of martensite variant microstructures in grains by nanoscale orientation mapping in TEM. The stress induced martensitic transformation generating recoverable transformation strain as well as plastic strain is not completed at the end of the upper stress plateau. The higher is the test temperature, the larger is the volume fraction of retained austenite as well as the plastic strain. The martensite variant microstructures in NiTi wire deformed up to the end of the stress plateau at 120 °C contain partially detwinned single domains of (001) compound twin laminate filling entire grains. It is proposed that the stress induced martensitic transformation proceeds via habit plane interface between austenite and second order laminate of (001) compound twins and that the martensite promptly reorients and deforms plastically by dislocation glide in the [100](001) slip system. When the wire is loaded further beyond the end of the stress plateau, the stress induced martensitic transformation continues and the martensite deforms plastically. It is concluded that the observed gradual loss of superelastic functionality of NiTi with increasing temperature does not originate from the plastic deformation of austenite, as widely assumed in the literature, but that it derives from the loss of resistance of the stress induced martensite to the plastic deformation under increasing stress.

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.

Nonlinear response of a multidirectional negative‐stiffness isolation system via semirecursive multibody dynamic approach

AbstractThis paper investigates an innovative negative‐stiffness device (NSD) that modifies the apparent stiffness of the supported structure for seismic isolation. The NSD comprises a lower base on the bottom and a cap on the top, together with a connecting rod, vertical movable wall, and compressed elastic spring, as well as circumferentially arranged, pretensioned external ropes, and inclined shape memory wires. This configuration can deliver negative stiffness and energy dissipation in any direction within the horizontal plane. A numerical model of the device is developed through a two‐step semirecursive method to obtain the force–displacement characteristic relationship. Such a model is first validated through comparison with the results obtained via the commercial software ADAMS. Finally, a large parametric study is performed to assess the role and the influence of each design variable on the overall response of the proposed device. Useful guidelines are drawn from this analysis to guide the system design and optimization.

Reconstruction of martensite variant microstructures in grains of deformed NiTi shape memory alloy by TEM

Two transmission electron microscopy (TEM) based methods were applied to reconstruct martensite variant microstructures in entire grains of plastically deformed nanocrystalline NiTi wires. First method consists in manual TEM analysis of composite electron diffraction patterns and dark field images of microstructures taken using carefully selected Bragg spots. Second method involves automated orientation/phase mapping of martensite variant microstructures in TEM (ASTAR). Application of these two methods helped us to discover new mechanism of the plastic deformation of monoclinic B19’ martensite in NiTi shape memory alloys called kwinking as it combines dislocation slip based kinking and deformation twinning in martensite.In this work, we describe how the martensite variant microstructures in nanograins of plastically deformed NiTi shape memory wire are reconstructed using the TEM based methods and discuss their advantages and disadvantages. The application of the first manual method requires tilting the TEM lamella so that all martensite variants in the analysed grain are oriented in a common low index zone. Such common crystal lattice direction exists in each grain of plastically deformed martensitic NiTi wire because the microstructures were created by the kwinking deformation mechanism. The requirement to orient the selected grain into a common unique direction in monoclinic lattice, on the other hand, is not unique to kwinking and represents a severe limitation of the SAED-DF method due to the constraints on tilting the TEM lamella. Application of the automated crystal orientation mapping ASTAR method enables detailed orientation analysis of nanoscale martensite variant microstructures in generally oriented grains of deformed NiTi wires as well as pointwise ex-situ analysis of interfaces with excellent resolution in real and orientation space.

Microstructural characterization and analysis of nitinol-based self-healing metals matrix composite of A356 alloy produced by high-pressure die casting

A self-healing non-ferrous metal-matrix composite is prepared by the high-pressure die-casting process. It includes casting set-up, sample preparation of metal matrix composite (MMC), microstructural characterization, and analysis of its ability to close the crack. Aluminum alloy (A356) is deployed as a matrix material in the MMC. Nitinol is a smart alloy produced by a combination of Nickel and Titanium in equal mass proportion. Apart from excellent mechanical properties it also exhibits super-elasticity and shape-memory effect. The wire of the Nitinol is integrated as reinforcement within the matrix of A356 alloy through a high-pressure die-casting process. The recovery percentage of the metal matrix composite and microstructural evaluation are reported. The deployment of shape memory wire provides the ability to recover the matrix material even from plastic strain by just heating the sample slightly above the activation temperature of the Nitinol wire. Microstructural evaluation indicates fair integration of the reinforcement within the matrix material. Gaining the ability for 30.27% angular restoration and 19.37% crack closer is a very positive sign for designing self-healing metallic materials.

Trajectory tracking control of parallel manipulator actuated with shape memory wire

This study describes the design of a parallel spatial manipulator with four degrees of freedom actuated with shape memory alloy (SMA) wire to validate the use of SMA in complicated mechatronics systems. The manipulator has a closed kinematic structure, which includes a fixed base and a moving square platform (end effector). The four arms of the manipulator are SMA wires fastened between the fixed base and the end effector. SMA wire-based actuators replace bulky conventional revolute actuators. This work spotlights the development of an actuator model, dimensional analysis, and design of cascade control strategies of various PID and sliding mode controller in their integral and fractional order configurations. Experimental evaluation of the actuator is performed through trajectory tracking to quantify the different controller configurations. The experimental results indicate that the parallel manipulator associated with SMA wire actuators is the best alternative to conventional motion stages for highly precise micro-positioning and tracking applications in the fields of 3D printing, intricate surgical operations, the medical and pharmaceutical industries, and flight and gaming simulators.

Temperature-Controlled Laser Processing of Shape Memory Wires: Spherical Ends as Connectors for System Integration

Nickel–Titanium-based shape memory alloys have reached a high technological relevance in the medical field and also for actuation/energy conversion. At present, the interest in new actuation solutions is steadily increasing. However, one important challenge for the design of new actuators is the lack of connection and coupling options, which often hinders a reliable system integration. To address this challenge, this study presents a temperature-controlled laser processing approach for the generation of spherical ends on shape memory wires, which allow a relatively simple integration into different types of systems (e.g., printed circuit boards) in a form-fitting manner. For this purpose, an experimental setup with an integrated pyrometer was used to establish spherical ends on thin NiTi wires with a diameter of 0.24 mm. The resulting microstructures and the functional properties were investigated using scanning electron microscopy, thermal analysis, uniaxial tensile testing, actuation fatigue testing, and hardness measurements. The results obtained in the present study indicate that our laser procedure successfully yields reliable connection options for NiTi wires, without harming the functional performance of the material.

Room-temperature elastocaloric effect in Co49Ni21Ga30 shape memory wires

We demonstrate appreciable room-temperature elastocaloric effect in the Co49Ni21Ga30 microwires prepared using the Taylor-Ulitovsky method. By forming an almost excellent [001]B2-oriented single crystal along the wire axis, extraordinary superelasticity with low critical stress and narrow stress hysteresis was achieved. Moreover, the wire exhibits room-temperature elastocaloric effect (ΔTad = −4.1 K) with no apparent degradation for 100 cycles. Due to its easy fabrication and the small scale, the wire is of great potential for advanced applications in miniature intelligent devices requiring refrigeration. This work also paves the way for developing other high-performance shape memory wires.

Comprehensive study of microstructure, phase transformations, and mechanical properties of nitinol alloys made of shape memory and superelastic wires and a novel approach to manufacture Belleville spring using wire arc additive manufacturing

In the present work, using wire arc additive manufacturing (WAAM), a novel approach is implemented to manufacture the Belleville spring/washer made from superelastic (SE) and shape memory (SM) Nitinol (NiTi) wires. A detailed correlation between the chemical composition, microstructure, and martensite transformation of deposited layers and their mechanical properties has been established. The energy dispersive spectroscopy (EDS) results revealed that the first track deposited using both SE and SM effect wire consisted of significant Fe constituents, which was further reduced while increasing the number of tracks. Moreover, as compared to the sample manufactured with SE effect NiTi wire (S1), the X-ray diffraction (XRD) of the sample manufactured with SM effect NiTi wire (S2) showed a secondary phase like NiTi2 along with the major NiTi (B19′ martensitic). It has been found that the presence of Ni4Ti3 precipitate in the microstructure of SE causes an enhanced superelasticity desired for the Belleville spring applications. Furthermore, the mechanical properties, microstructure, and phase transformation temperature of both S1 and S2 were investigated and compared. It was found that S2 has a finer microstructure than S1. Also, the compressive strength and hardness of S2 were higher than that of S1. In contrast, the tensile strength of the S2 was found to be lower than the S1. Regarding manufacturing the Belleville spring using WAAM, S1 showed promising mechanical and martensitic transformation results.

Healing effect of electric current treatment on superelasticity and elastocaloric effect of TiNi shape memory wire

This study investigated the healing effects of electric current treatment on Ni-rich TiNi shape memory wire after every 100 superelastic cycles. The diameter of the TiNi wire was 0.5 mm. The electric current treatment was applied without removing the wire from the tensile machine, aiming for online healing of the shape memory alloy. The electric current treatment showed an obvious healing effect, which restored the superelastic and elastocaloric properties of the functionally degraded TiNi shape memory wire. With treatment conditions of 20.4 A/mm2 and 2 min (the temperature of the wire increased up to 280 °C in 10 s), the elastocaloric temperature rise and drop of the TiNi wire recovered about 14% and 6% after 3–4 treatments, respectively, as compared with the case without any heat treatment. TEM observations indicated that the residual martensite introduced into the TiNi wire during superelastic cycles could be eliminated through the electric current treatment. Experimental results demonstrated that electric current treatment was a promising method to restore the functionality of the TiNi SMA wire after several superelastic cycles without the need to remove the wire from the apparatus, which would thus improve the performance of shape memory alloys during their long-term application.

Dynamic experimental study of nitinol wire-reinforced composite structures

Due to the advantages of both the metallic and glass fiber qualities, glass fiber reinforced metal layers are one of the best impact resistant materials. Shape memory alloys have also been thought to be effective materials for equipping the traditional impact-exposed materials due to their high impact damping capabilities. The modal response (natural frequencies, damping, and vibration amplitude) of the laminate composite constructions that incorporate shape memory wires was experimentally investigated in this article. The goal of the current research is to ascertain how the modal responses are impacted by three production parameters: wire diameter, wire location, and wire number. Using an experimental design plan and a central composite design, hybrid specimens were planned. The results showed that the manufacturing variables influence all the modal responses in different proportions. Regarding the innovations in the construction of this type of hybrid composite, this study could be used in the design of mechanical and airspace structures.

Modulated martensite in NiTi shape memory alloy exposed to high stress at high temperatures

NiTi shape memory wire was deformed in martensite state at low temperature −125 °C up to 750 MPa stress and subsequently heated far above the Af temperature while the stress 750 MPa was held constant. Under such conditions, the heated B19’ martensite in the wire was driven towards its thermomechanical stability limits and eventually transformed into plastically deformed austenite. In order to evaluate the mechanism by which such highly constrained reverse martensitic transformation proceeds, martensite variant microstructures and lattice defects evolving in the heated wire were analyzed by TEM and HRTEM.It is found that, the oriented B19’ monoclinic martensite deformed plastically via kwinking deformation involving coordinated dislocation slip and twinning and simultaneously adopted a long period modulated crystal structure, before it transformed to austenite upon heating under applied stress. It is proposed that the modulated martensite structure forms from the B19’ structure via coordinated slip of partial dislocations with Burgers vector b = a/2 [100] on (001) crystal planes. Coordinated slip was enforced by the kwinking deformation and partial dislocations started to glide because the martensite was exposed to elevated temperatures. Plastic deformation of oriented B19’ martensite enabling the reverse martensitic transformation upon the constrained heating is discussed in view of its impact on NiTi functionality in engineering applications.

Plastic deformation of B19’ monoclinic martensite in NiTi shape memory alloys: HRTEM analysis of interfaces in martensite variant microstructures

Martensite variant microstructures in grains of nanocrystalline NiTi shape memory wire deformed in tensile test at room temperature up to 15% strain were analyzed in transmission electron microscope (TEM) with the aim to reveal the mechanism of plastic deformation of B19’ monoclinic martensite which created these microstructures. The analysed microstructures consisted of parallel and/or wedge arranged deformation bands within the martensite matrix oriented in a common <010> low index zone. High resolution TEM (HRTEM) analysis of 35 interfaces within a single grain was performed. The observed interfaces were reasonably planar on mesoscale of individual grains but highly irregular on atomic scale. Majority of analysed interfaces displayed interface planes and lattice misorientations similar to (100), (20-1) and (10-1) martensite twins, but not exactly, many interfaces deviated from the exact twin planes and misorientations. Some interfaces displayed crystal lattices only rotated within the <010> low index zone, i.e. lacking the mirror symmetry of adjoining lattices characteristic for twins. On the other hand, traces of (001) crystal planes were mirror symmetric across all observed interfaces. These experimental observations were rationalized by assuming that the analysed martensite variant microstructures were created by the plastic deformation of B19’ martensite by kwinking deformation proceeding via coordinated [100](001) dislocation slip based kinking combined with (100) twinning.

Fabrication, testing, and microstructural analysis of nitinol-based self-healing metal matrix composite of A356 alloy cast by semi-solid metal processing

ABSTRACT The self-healing of metallic material is a relatively new area in materials engineering. It is inspired by the biological process of healing. This work analyzes the self-healing behaviour of metals-matrix composite. The semi-solid metal processing technology was opted to prepare an aluminium-based self-healing metal-matrix composite. Nitinol is the alloy produced by combining nickel and titanium in a 1:1 ratio, with the wires of the same incorporated within the aluminium matrix during the process. Analysis of the recovery rate of the self-healing material and microstructural investigation of the metal matrix composite is the objective of this research work. The deployment of shape memory wire provides the ability to recover the matrix material even from plastic strain. Nitinol exhibits a shape memory effect by the transformation of the phase. Integration of A356 alloy with nitinol wire enables the material to regain its original shape and dimension by heat as an external stimulus. Semi-solid metal process via rapid slurry formation technique handled delicately so that self-healing effect should not diminish. Microstructural evaluation indicates fair integration of the reinforcement within the matrix material. Analysis of crack closure shows 44.277% positive recovery of the deformed surface.

Self-healing performance of a microcapsule-based structure reinforced with pre-strained shape memory alloy wires: 3-D FEM/XFEM modeling

Combination of microcapsules and shape memory alloys (SMAs) is one of the promising self-healing mechanisms. Although there are several parameters which affect the performance of such structures, limited studies are performed on this combined healing mechanism. In this work, we study the performance of such a composite structure using a 3-D finite element and extended finite element model consisting of matrix, glass microcapsule, healing agent, and Ni-Ti SMA wire. After examining the results, the effect of shape memory alloy wires on increasing the maximum fracture stress was observed. Moreover, the effect of radius of shape memory alloy wires, initial crack location, thickness ratio and volume fraction of microcapsules, and interface strength on ultimate fracture stress are investigated. Also, as a key parameter in self-healing performance, the crack opening distance decreased from 5 to 0.008 μm using 0.5% volume fraction of shape memory wires without pre-strain. In the case that the wires have a pre-strain of 1%, this value reaches almost zero and a compressive stress is induced between fracture surfaces which can enhance the healing process and adherence of healing agent.

The effect of Nd:YAG laser pulse duration and post-weld heat treatment on the microstructure and mechanical properties of laser-welded NiTi shape memory alloy

The heat input is the most critical factor in pulsed Nd:YAG laser welding and affects the microstructure and mechanical behavior of the welded alloys. NiTi alloy has been used for various applications such as medical equipment and MEMS due to its unique shape memory effect, superelasticity, and excellent corrosion and fatigue performance. This research investigated the effect of heat input and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of similar NiTi shape memory wires joints. For this purpose, NiTi wires were welded with pulse widths of 5, 8, and 11 ms, and then, heat treatment was performed. Microstructures of the welded alloys were examined using optical and electron microscopes and chemical composition was analyzed with an EDS analysis system. The mechanical properties were evaluated using tensile and microhardness tests. A desirable NiTi SMA joint was achieved by Nd:YAG laser, and the properties were improved by following post weld heat treatment.Investigations showed that microstructure and mechanical properties were changed by increasing the heat input. After applying PWHT due to recrystallization and the creation of new phases in the weld zone, the final strength of the joints increased up to 80%, and the behavior of the plateau region became similar to shape memory behavior in the NiTi alloy.