Ultralight shape memory actuator from wire-woven Kagome truss

There are two different ways of using shape memory alloy (SMA) wire as an actuator for shape control of flexible structures: it can be either embedded within the composite laminate or externally attached to the structure. As the actuator can be placed at different offset distances from the beam, external actuators produce more bending moment and, consequently, considerabnle shape changes with the same magnitude of actuation force compared with the embedded type. Such a configuration also provides faster heat transfer rate owing to convection, which is very important in shape control applications that require a highfrequency response of SMA actuators. Although combination and physics-based modeling of externally attached SMA actuator wires and strips have been considered by many researchers, these studies have some drawbacks, which, if neglected, result in a number of errors in the theoretical results compared with experimental results. These shortcomings are considering the linear Euler-Bernoulli beam theory, not deriving the actuation force of the SMA from the constitutive equations, and taking into account the effect of only one SMA wire actuation force on, for example, the structure. These assumptions may lead to erroneous theoretical modeling results compared with experimental results. In this study, the aforementioned difficulties of attaching SMA actuators to the smart structures have been addressed. In other words, instead of linear beam theory, nonlinear beam theory is used in system modeling and, therefore, the proposed method and results are valid in large deflection and rotation behavior of beam. Also, in comparison to many other analyses that the effect of only one SMA wire is investigated, in the present research the effect of all active and inactive SMA wires is considered. Accordingly, the result of this paper can easily be generalized to the structure with several SMA wire actuations. Moreover, with the purpose of having practical applications in modeling and control, the heat transfer equations of all SMA wires are considered in the analysis and, as a result, the control inputs of the presented model are SMA wire electric currents rather than SMA temperatures. First, a flexible beam actuated by two active SMA actuators is modeled. Then, the Brinson constitutive equations and thermoelectric equations for SMA materials are coupled with the nonlinear beam behavior, and the coupled system of equations is numerically solved for some particular practical cases. Finally, the numerical results of the model simulation are verified against the experimental results using a test setup to validate the proposed model prediction. The implemented method used in this paper can be easily extended to the more complex smart structure with numerous externally attached SMA wires.

This paper presents an experimental-analytical study on the active tuning of composite beams using Shape Memory Alloy (SMA) wires. Composite beams with fused silica tubes and `dummy' wires were manufactured first using autoclave molding techniques and then the `dummy' wires were replaced by pre-strained SMA wires. The beam and SMA wire were independently clamped at both ends. The SMA wires were activated using electrical resistive heating and a large tensile recovery force developed in them due to the mechanical constraints provided by the clamps. The influence of this recovery force on the vibration behavior of composite beams was determined by conducting vibration testing. Analytically, these beams with SMA wires inserted in embedded sleeves were examined as beams on an elastic foundation: the spring constant of the elastic foundation depended on the axial recovery force of SMA wire. Good correlation between analysis and experiment was achieved. A numerical parametric study of natural frequencies of composite beams with activated SMA wires was conducted. The parameters considered were the diameter, number of SMA wires and constituent of composite beam. The numerical study suggests that inserting 25 SMA wires of 20 mil diameter into a graphite-epoxy beam of 30 in. length, 1 in. width and 62 mils thickness increases its first frequency by 276%.

This study presents an experimental characterization of the interface strength of the shape memory alloy hybrid composite (SMAHC) consisting of the two‐way effect NiTi shape memory alloy (SMA) wire structured by electrochemical etching and the surrounding thermoset matrix. Mechanically induced, in situ thermally induced, and cyclic load‐increase pull‐out tests consistently reveal that SMAHC with structured SMA wires outperforms those with as‐delivered SMA wires by a substantial factor of 2.6–2.7 in interfacial strength — the critical factor governing the overall performance and functionality of the composite. Analyzing the force–displacement curves from mechanically induced pull‐out tests demonstrates that structuring the SMA wire surface leads to a significantly increased elastic energy to initiate a crack and achieve complete failure. SMA wires with structured surfaces continue transferring load even after the initial interfacial failure due to the presence of intact mechanical interlocking sites. The cyclic load‐increase pull‐out test confirms that SMA wires with structured surfaces exhibit a significantly higher load‐bearing capacity, withstanding more load levels and demonstrating greater force of the first failure. Furthermore, in thermally induced pull‐out tests with structured SMA wires, a re‐initiation of failure from the lower side follows an initial failure progression at the SMA wire entry point.

This study used two forms of shape memory alloy (SMA) wires, nickel–titanium–niobium (NiTiNb) and nickle–titatanium (NiTi), to retrofit reinforced concrete (RC) columns with lap splices. NiTiNb shape memory alloys are considered to show a wider temperature window compared with NiTi shape memory alloys and thus may be beneficial for applications in the area of civil structures. The goals of this study are to assess the mechanical behaviour of the two shape memory alloy wires and investigate the seismic performance of the shape memory alloy wire jackets for reinforced concrete columns with lap splices. First, the study investigates the recovery and the residual stress of NiTiNb and NiTi shape memory alloy wires. This study also evaluates the behaviour of the NiTiNb shape memory alloy wire under residual stresses. The results indicate that the shape memory alloy wire jackets show good performance for reinforced concrete columns with lap splices. The shape memory alloy wire jackets increase the ductile behaviour of the lap-spliced columns without strength degradation. The results show that their performance is superior to that of the RC column with continuous reinforcements. The study shows that the NiTiNb shape memory alloy wire jackets are more adaptive for retrofit of RC columns than the NiTi shape memory alloy wire jackets since the NiTiNb shape memory alloy shows more appropriate temperature windows for the applications of shape memory alloys in civil structures.

This paper presents a first concept of a new biomimetic transradial prosthetic arm design, called ‘MataPro-1,’ that features a 3D-printed hand bone structure that mimics the shape of human finger phalanges and palm bones, flexible elastic joints, artificial muscles, and silicone flesh that covers and protects the internal components, provides restoring force, enables better gripping capability, and appears cosmetically realistic. The artificial muscles that actuate MataPro-1 are shape memory alloy (SMA) wires, which ensure effective grip strength for many everyday objects, without causing any noise. In order to avoid the need to cool SMA wires in the small volume of the fingers, the SMA wires are not routed through the finger phalanges. The SMA wires are spooled in the forearm, cooled by a fan only during the finger restoration process, and are connected to steel wires that are routed through the finger phalanges. The finger restoring force provided by the flexible joints and silicone flesh acts as bias force for SMA wires, avoids the need for antagonistic SMA wires, and speeds up the finger restoration process. The control system of MataPro-1 is intuitive and non-invasive achieved by voice recognition phone application, or an EEG headset that monitors brainwaves and facial expressions. MataPro-1 was successful in gripping different objects of various shapes, weights and sizes in multiple different gripping positions.

Morphing wings have various possibilities to realize drag and noise reduction and to extend flight envelope by smoothly changing wing shape during flight. This study focuses on the application of Shape Memory Alloy (SMA) wires as a lightweight actuation mechanism for morphing wings because SMA has a large recovery stress per unit mass. To achieve the required actuation stroke for the SMA wires, it was considered to design the spiral configuration of the SMA wires. This research experimentally observes the relationship between the recovery strain as the actuation performance of tube-guided wires and its geometric parameters such as spiral angle. It was found that the friction force between the SMA wire and its spirally guiding tube plays an important role on the actuator performance, and the performance gradually decreased as the length of the wires and the number of spirals increased. Furthermore, the application of the spiral configuration of SMA wire for a small aircraft was investigated. As a result, the effectiveness depends on the coefficient of the friction between the SMA wire and the spiral tube. Thus, the results obtained in this study could be used to properly design the tube-guided SMA coil-type actuators for morphing wings considering the effectiveness and challenges in its implementation.

A design approach for a rotatory joint actuator using a contractile shape memory alloy (SMA) wire is presented and an example design is followed. In this example, the output torque of the actuator is 18 Newton-meters, and its angular range is 30 degrees. Compared with a SMA spring type actuating component, a SMA wire type actuating component uses less SMA material and uses less electrical energy when it is electrically powered. On the other hand, a SMA wire type actuating component must have a large SMA wire length to produce a required amount of angular rotation of the joint. When pulleys are used to arrange a lengthy SMA wire in a small space, the friction between pulleys and pins is introduced and the performance of the joint actuator is degenerated to some degree. The investigated joint actuator provides a good chance for developing powered orthoses with SMA actuators for disabled individuals. It can relieve the weight concern with hydraulic and motor-powered orthoses and the safety concern with motor-powered orthoses. When electrically powered, a SMA actuator has the disadvantage of low energy efficiency.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents a design study of adaptive skins that enable thermal regulation for buildings. The skins consist of rectangular panels that adaptively open and close driven by shape memory alloy (SMA) wires in response to the variation of the environment temperature. The SMA wires are used as both thermal sensors and actuators that inspect the environmental temperature and provide a corresponding actuation response. When temperature is low, the SMA wires are stable in their elongated martensitic configuration, keeping the panels closed to maintain the building interior warm by reducing incoming airflow from the exterior. When temperature reaches the SMA austenite transformation values, the SMA wires transform into their contracted austenitic configuration and open the panels. This permits cooling of the building interior by allowing circulation of incoming airflow from the exterior. This repeatable response allows the skins to adaptively regulate the indoor temperature. The performance of the adaptive skins is evaluated using finite element analysis. Metallic and laminated fiber-reinforced composite plates are explored as material options for the panels. The adaptive skins are parameterized using design variables including the dimensions of the panels, the ply thickness and orientation angles in the case of fiber-reinforced panels, and the radii of the SMA wires. By employing genetic algorithms, these design variables are optimized to maximize the achievable opening area of the panels while satisfying material failure constraints.

This study used prestrained NiTiNb and NiTi shape memory alloy (SMA) wires to confine concrete cylinders. The recovery stress of the wires was measured with respect to the maximal prestrain of the wires. SMA wires were preelongated during the manufacturing process and then wrapped around concrete cylinders of 150 mm×300 mm (ϕ×L). Unconfined concrete cylinders were tested for compressive strength and the results were compared to those of cylinders confined by SMA wires. NiTiNb SMA wires increased the compressive strength and ductility of the cylinders due to the confining effect. NiTiNb wires were found to be more effective in increasing the peak strength of the cylinders and dissipating energy than NiTi wires. This study showed the potential of the proposed method to retrofit reinforced concrete columns using SMA wires to protect them from earthquakes.

Scalable rotary actuators are being developed with the help of Shape Memory Alloy (SMA) wires. Subjected to elevated temperatures SMA wires deliver large strains and high stresses. Yet their bandwidth is limited because of the time required for cooling. Bandwidth can be enhanced by miniaturizing the actuating system, which results in higher cooling rates. Using SMA wires with diameter of about 100 micron, several miniature actuators have been designed and fabricated. For example, a rotary joint with bi-directional actuation, which is about 4mm wide, 9mm long and 3mm high, can achieve angular deflection of around +/- 60 deg. Based on this bi-directional actuator, SMA ratchet mechanisms with minimum feature sizes of about 200 micron have been developed. The ratchet mechanisms can transform angular motion to continuously rotating motion. SMA wires are embedded into polyurethane structures using Shape Deposition Manufacturing (SDM). SDM is a layered manufacturing process capable of building complex 3D parts through the combination of material addition and subtraction. A key advantage of this process is the ease by which process interruption may occur to embed sensors and actuators into components. SDM can also fabricate functional mechanisms in an assembled configuration eliminating the need for assembly. The present article will describe design and manufacturing processes which enable the fabrication of the scalable rotary actuators. System performance and behavior of the SMA actuators will be also discussed in this contribution.

In the present article, the dynamic behavior of sandwich plates with embedded shape memory alloy (SMA) wires is evaluated for two cases wherein (i) the stress-strain curve of the superelastic behavior of the SMA wires is symmetric and (ii) the mentioned curve is non-symmetric. A modified version of Brinson’s constitutive model is proposed and used. The high non-linearity in the behavior stems from the SMA wires embedded in the sandwich plate. In this regard, in addition to the proposed advanced algorithm for the determination of the martensite volume fraction, a Picard iterative solution algorithm is used in conjunction with Newmark’s numerical time integration method for solving the resulting finite element equations. To improve the accuracy of the results, the variation of martensite volume fraction and material properties of individual points of the structure are updated continuously. Therefore, the kinetic equations of the phase transformation of the SMA are coupled with the motion equations, to accurately model the nonlinear behavior of the sandwich plate. For analysis of the thick sandwich plate, a higher-order global-local theory with novel 3D-equilibrium-based corrections is utilized. One of the features of this theory is the estimation capability of the nonlinear in-plane displacement components, and precise assessment of the transverse shear stresses through satisfying the continuity conditions of the shear stresses at the interfaces between layers. Another advantage of the proposed theory in comparison with the conventional approaches is the ability to simulate changes in the core thickness. This is especially important in cases where the core is relatively thick or soft.

Bond strength of concrete confined by SMA wire jackets

Current treatments for gait pathologies associated with neuromuscular disorders may employ a passive, rigid brace. While these provide certain benefits, they can also cause muscle atrophy. In this study, we examined NiTi shape memory alloy (SMA) wires that were annealed into springs to develop an active, soft orthotic (ASO) for the knee. Actively controlled SMA springs may provide variable assistances depending on factors such as when, during the gait cycle, the springs are activated; ongoing muscle activity level; and needs of the wearer. Unlike a passive brace, an active orthotic may provide individualized control, assisting the muscles so that they may be used more appropriately, and possibly leading to a re-education of the neuro-motor system and eventual independence from the orthotic system. A prototype was tested on a suspended, robotic leg to simulate the swing phase of a typical gait. The total deflection generated by the orthotic depended on the knee angle and the total number of actuators triggered, with a max deflection of 35°. While SMA wires have a high energy density, they require a significant amount of power. Furthermore, the loaded SMA spring response times were much longer than the natural frequency of an average gait for the power conditions tested. While the SMA wires are not appropriate for correction of gait pathologies as currently implemented, the ability to have a soft, actuated material could be appropriate for slower timescale applications.

This paper presents the design and the experimental result of the active position control of a shape memory alloy (SMA) wire actuated composite beam. The composite beam has a honeycomb structure with SMA wires embedded in one of its face sheets for the active actuation. The potential applications of this experiment include thermo-distortion compensation for precision space structure, stern shape control for submarines, and flap shape control for aeronautical applications. SMA wires are chosen as the actuating elements due to their high recovery stress (>500 MPa) and tolerance to high strain (up to 6%). However, SMA wires are inherently nonlinear and pose a challenge for control design. A robust controller is designed and implemented to actively control the tip position of the composite beam. The experiment set-up consists of the composite beam with embedded SMA wires, a programmable current/voltage amplifier to actuate the SMA wires, an infrared laser range sensor to detect the beam tip displacement, and a real-time data acquisition and control system. The experimental result demonstrates the effectiveness of the robust control.

The aim of this research is to analyze buckling and bending behavior of a sandwich Reddy beam with porous core and composite face sheets reinforced by boron nitride nanotubes (BNNTs) and shape memory alloy (SMA) wires resting on Vlasov\'s foundation. To this end, first, displacement field\'s equations are written based on the higher-order shear deformation theory (HSDT). And also, to model the SMA wire properties, constitutive equation of Brinson is used. Then, by utilizing the principle of minimum potential energy, the governing equations are derived and also, Navier\'s analytical solution is applied to solve the governing equations of the sandwich beam. The effect of some important parameters such as SMA temperature, the volume fraction of SMA, the coefficient of porosity, different patterns of BNNTs and porous distributions on the behavior of buckling and bending of the sandwich beam are investigated. The obtained results show that when SMA wires are in martensite phase, the maximum deflection of the sandwich beam decreases and the critical buckling load increases significantly. Furthermore, the porosity coefficient plays an important role in the maximum deflection and the critical buckling load. It is concluded that increasing porosity coefficient, regardless of porous distribution, leads to an increase in the critical buckling load and a decrease in the maximum deflection of the sandwich beam.