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The soft actuators of smart materials have attracted significant attention in recent years due to their unique functions and distinctive characteristics. The actuators are composed of smart materials that can demonstrate substantial alterations in their dimensions, shape, or mechanical characteristics when subjected to external stimuli, including but not limited to temperature, light, electricity, or magnetic fields. These aforementioned characteristics render them highly advantageous for various applications, including tissue engineering, prosthetics, surgical robots, drug delivery, and soft robotics. A deeper understanding of the principles of the actuators is crucial for their development and application expansion. This article provides a comprehensive analysis of soft actuators made from smart materials, explaining their underlying concepts, operational mechanisms, material composition, production techniques, and the diverse range of applications across various fields, including tissue engineering, prosthetics, surgical robotics, drug delivery systems, and the emerging field of soft robotics. This review further highlights the current challenges and prospects to address these problems to enable their ability to revolutionize into a variety of different technical fields. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are widely used across various industries, including medicine, due to their inherent properties such as the shape memory effect, pseudo-elasticity, antigenicity, decomposition, biodegradability, biocompatibility, resistance to corrosion, and wear. This review article aims to cover different aspects of SMAs, including their fundamental concepts such as origin, exceptional properties, fabrication techniques, and structural analysis. Exploring the SMAs at the nanoscale using molecular dynamics analysis and recent studies that integrate machine learning techniques. Finally, the article concludes with a discussion of various applications of SMAs, considering the properties and potential fields of use. [ABSTRACT FROM AUTHOR]

Novel earthquake‐resistant materials are of interest to the academic community because they have the potential to reduce seismic residual displacements and, by extension, maintenance costs. Smart materials and technologies have enhanced the seismic response of reinforced concrete (RC) buildings, but the effect of these advancements on issues that arise after earthquakes in RC‐coupled walls has not yet been investigated. This research scrutinizes the seismic performance of RC‐linked walls reinforced with NiTi, FeNCATB, and CuAlMn superelastic shape memory rebar in the boundary regions. As a part of the case study, three RC‐linked wall systems with four, eight, and twelve stories were adopted. The highest critical values for the inter‐story drift ratio (IDR) and the residual inter‐story drift ratio (RIDR) were obtained through the OpenSees program. According to the results, RIDR markedly reduces whenever concerns about the quake's aftermath are highlighted. In accordance with findings, among the whole adopted shape memory alloy (SMA) types in this research, the RC‐coupled wall based on Cu demonstrates superior results concerning RIDR and performs adequately regarding the restoring effect. As a result, seismically involved areas exposed to significant ground motions are typically recommended to use Cu‐based SMA material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Auxetic metamaterials, characterized by their negative Poisson's ratio, have garnered significant interest in various fields due to their unique mechanical properties. This article presents a pioneering approach to the development of auxetic smart metamaterials using shape memory alloy (SMA) as the core material. As SMAs can be Joule heated to change between their low‐ and high‐temperature phases to trigger the actuation of the structure, the auxetic smart metamaterial can actively modify its shape and stiffness to produce bidirectional actuation with a single power input and using a single bias mechanical element. The proposed active auxetic metamaterial consists of an SMA plate patterned with auxetic cuts, creating hinges that modulate the deformation of the structure to produce an auxetic behavior. This work looks at the impact of different geometric parameters on the behavior of the structure, including its generated force, its maximum strain, and its Poisson's ratio. The study also investigates the effect of the number of segmented units, revealing that designs with more segmented units suffer from stress concentrations near attachment points, limiting their advantages. This article shows that smart materials can help imbue metamaterials such as auxetic metamaterials with active properties to facilitate their implementation in future robotic applications. [ABSTRACT FROM AUTHOR]

Exploring shape memory alloys (SMAs) is like diving into a world of material magic, especially when combined with additive manufacturing techniques. This detailed assessment delves into the fascinating realm of additive manufactured SMAs, examining their complex fabrication processes, captivating internal structures, wide-ranging applications, and unique properties. It is remarkable to observe how the combination of metals, particularly nickel and titanium, creates the very essence of SMA's capabilities and various other material combination for novel SMAs. Additional insights are provided regarding how additive manufacturing parameters and appropriate post-treatments can enable these materials to accomplish extraordinary functionalities. These SMAs also possess the ability to recollect and move, demonstrating superelasticity and the capacity to regain their original shape in various capacities. However, there are promising prospects for the development of novel SMA mixtures, enhanced post-treatments methods, and even more intelligent and responsive products with dimensional accuracy and uniformity. This work presents insights on opportunities in industries for resilient materials, ranging from everyday devices to the immense expanse of space and the human body. Even with the advancements, there is still work to be done in continuously improving their design and pocket comfort. This review not only presents information but also envisions a future in which additive manufactured SMAs are central to advancements in engineering and other fields.

The increasing demand for innovative grippers and actuators for the automation sector encourages the development of new and innovative functional principles. Intelligent materials are particularly suitable for this purpose based on their high energy density. In this study, a two-finger gripper driven by shape memory alloys (SMA) for use in automation technology is presented. Previous grippers driven by SMA can only be found in the field of micro gripping due to the limited stroke generated by SMA. Based on a methodical product development, a new type of gripper was developed and is presented in this study, which can achieve an opening width comparable to conventional grippers based on transmission mechanisms. Two different variants of the gripper are shown and compared aiming to minimize the installation space and weight of the gripper. In addition to the design presentation, a prototype is built, and the functionality is demonstrated through various test series. [ABSTRACT FROM AUTHOR]

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Implementing smart materials as an actuator in fabricating micro-positioning systems has become pervasive in recent years. However, the application of Shape Memory Alloy (SMA) smart materials is limited due to its complex nonlinear mechanical behavior, such as asymmetric hysteresis and saturation characteristics. One of the most potent experimental-based methods of modeling these nonlinearities is the Generalized Prandtl-Ishlinskii (GPI) model. Unlike similar methods such as the Preisach model, this model is analytically invertible. This study aims to develop a micro-positioning stage and identify an experimental-based model describing the system response. The model structure is composed of two cascade sub-models. In the first sub-model, which models the actuator thermal behavior, the parameters of a linear dynamic model are identified. This sub-model predicts the actuator temperature given the electrical current. The second sub-model estimates the phase transformation and consequently the actuator displacement as a function of temperature. The GPI structure has been used for constructing the Wiener sub-model. The experimental and numerical results showed that the proposed black box model can accurately describe the system behavior, although identifying a comprehensive model to adequately describe the SMA actuator is a great challenge. [ABSTRACT FROM AUTHOR]

The emergence of materials that can effectively convert photon energy (light) into motion (mechanical work) and change their shapes on command is of great interest for their potential in the fabrication of devices (powered by light) that will revolutionize the technologies of optical actuators, smart medical devices, soft robotics, artificial muscles and flexible electronics. Recently, metal–organic crystals have emerged as desirable smart hybrid materials that can hop, split and jump. Thus, their incorporation into polymer host objects can control movement from molecules to millimetres, opening up a new world of light-switching smart materials. This feature article briefly summarizes the recent part of the fast-growing literature on photomechanical properties in metal–organic crystals, such as coordination compounds, coordination polymers (CPs), and metal–organic frameworks (MOFs). The article highlights the contributions of our group along with others in this area and aims to provide a consolidated idea of the engineering strategies and structure–property relationships of these hybrid materials for such rare phenomena with diverse potential applications. [ABSTRACT FROM AUTHOR]

Cu–Al–Fe shape memory alloys are a new kind of smart materials with high phase transition temperature. However, poor thermal stability and poor shape memory effect limit the commercial application range. In this paper, the effect of Al content on microstructure, thermal stability, shape memory effect and mechanical properties of Cu–Al–Fe shape memory alloys was investigated systematically by changing Al content, so as to obtain the optimal composition ratio for better commercial application. The results show that in the as-cast state, the microstructure is a mixture of (Cu) phase, β′ martensite and Fe(Cu, Al) phase with Al content of 11 mass%, and a mixture of β′ martensite and Fe(Cu, Al) phase with Al content of 12 mass% and 13 mass%. After quenching, β′ martensite exists in all alloys, while (Cu) phase and Fe(Cu, Al) phase disappear, and γ′ martensite also exists at Al content of 13 mass%. The shape memory alloy effect of as-cast alloy is enhanced with the increase of Al content, while the shape memory effect of quenched alloy increases first and then decreases. Among them, Cu82Al13Fe5 has the best shape memory effect, the recovery ratio reaches 84.38%, and it also has the best thermal stability. [ABSTRACT FROM AUTHOR]

Zinc–iodine (Zn–I2) batteries are promising, low‐cost and safe aqueous rechargeable energy storage devices. An iodide shuttle‐induced corrosion and poor zinc (Zn) stripping/plating often result in a limited battery lifetime, urges the development of multifunctional Zn anodes. To overcome these problems, here multifunctional Zn‐anode is demonstrated with shape‐programmability and uniform Zn morphology along low‐indexed (002) crystal plane, achieved by electrodepositing Zn on nitinol alloy (nickel–titanium, NiTi). It is found that the surface oxide layer on NiTi supports the uniform Zn deposition with densely packed and planar film formation that leads high corrosion resistance, while adopts the shape‐memory function. NiTi‐based device achieves extremely steady performance, benefiting from uniform and planar Zn morphology during cycling, whereas the Zn‐based device short‐circuits due to dendritic development under severe iodide corrosion. It is also demonstrated a flat‐shape‐programmed flexible pouch cell Zn–I2 battery (SP‐ZIB), which performs well in bent mode, recovers its original flat shape at elevated temperature, and shows consistent performance for validated cycles. The shape‐memory function of NiTi makes this Zn–I2 battery advanced by flexibility and shape‐programmable features. This study represents fresh insight for using smart materials as multifunctional features for the next‐generation Zn‐I2 batteries. [ABSTRACT FROM AUTHOR]

The present work presents the investigation of the dynamics and influence of chaotic behavior on energy capture for a U-shaped structure (portal frame) that contains shape memory alloy (SMA), piezoelectric material (PZT), a nonlinear energy sink (NES) and a non-ideal excitation source represented by an unbalanced electric motor coupled to the U-structure. The mathematical model presents nonlinearities arising from the nonlinear stiffness of the U-structure, the NES system, the SMA, and the PZT material. Chaotic behavior is assessed through time history, bifurcation diagrams, phase diagrams, and the 0–1 test. Energy capture is carried out through a piezoelectric material (PZT), represented by a non-linear electromechanical coupling model, and electromagnetic induction generated by the non-linear electromagnetic energy sink coupled to the structure (NES). Dynamic analysis is performed through parametric analysis of parameters related to piezoelectric coupling and NES parameters. Numerical simulations demonstrate that the system has chaotic behavior for specific parameters and that its energy capture is influenced by parametric variation. It is shown numerically that the parameters of the SMA material, the PZT material, and the NES significantly influence the chaotic behavior and energy capture of the investigated electromechanical system. [ABSTRACT FROM AUTHOR]

The structural performance improvement of concrete members is by far a crucial theoretical issue for engineers, and the development of modern smart and composite materials makes it possible to gradually enhance the durability design of the concrete structure. In this study, six beams of the same size and reinforcement ratio, the proposed composite beam (SMA-GFRP-ECC) and five comparative beams (RC, R-ECC, SS-ECC, GFRP-ECC, SMA-ECC), were designed and tested under low-cycle unidirectional cyclic loading and unloading conditions. The energy dissipation capacity, displacement ductility, residual deformation, and self-repairing performance of each concrete beam were evaluated. Afterward, a concise calculation model for the studied composite beam is deduced and developed based on the existing relevant constitutive models and concrete assumptions. The test results indicate that compared with RC beams, the composite reinforced ECC beams show obvious multi-cracking and smaller crack width during the loading process and have good bending ductility. The innovative SMA-GFRP-ECC beam is capable of a high bearing capacity, ductility, and damage self-repairing. The new proposed beam has more than 80% of the maximum crack width recovery capacity during unloading. Hence, the proposed SMA-GFRP-ECC beam is a rather good first attempt of strengthened beams, combining the advantages of SMA, GFRP, and ECC. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA), a type of smart material, is widely used in the design of reinforcement and repair, isolation, and shock absorption of building structures because of its outstanding characteristics, such as the shape memory effect (SME), superelasticity (SE), and high damping. It not only improves the bearing capacity, ductility, and mechanical properties of the structural components of buildings but can also effectively slow down the strong response of engineering structures under the effect of an earthquake. It plays a key role in energy dissipation and shock absorption as well as sustainable development. To promote the application of SMA in building structures, this paper summarizes the research on the use of SMA as a reinforcing material in building structures, including work related to SMA material characteristics and types, SMA-reinforced structural components, and SMA isolation devices. In addition, the shortcomings of SMA applications in building structures are analyzed, and valuable suggestions for future research methods are put forward. SMA has been applied to engineering practice in the form of embedded and external reinforcement, which shows that it has broad application prospects in future buildings. [ABSTRACT FROM AUTHOR]

Stiffness regulation strategies endow soft machines with stronger functionality to cope with diverse application requirements, for example manipulating heavy items by improving structural stiffness. However, most programmable stiffness strategies usually struggle to preserve the inherent compliant interaction capabilities following an enhancement in structural stiffness. In this study, inspired by the musculocutaneous system, we propose a soft stimuli-responsive material (SRM) by combining shape memory alloy into compliant materials. By characterizing the mechanical performance, the flexural modulus increases from 6.6 to 142.4 MPa under the action of active stimuli, crossing two orders of magnitude, while Young's modulus stays at 2.2 MPa during programming structural stiffness. This comparative result indicates that our SRMs can keep a lower contact stiffness for compliant interaction although structural stiffness increases. Then, we develop three diverse soft machines to show the application potential of this smart material, such as robotic grippers, wearable devices, and deployable mechanisms. By applying our materials, these machines possess stronger load-bearing capabilities. Meanwhile, these demonstrations also illustrate the efficacy of this paradigm in regulating the structural stiffness of soft machines while maintaining their compliant interaction capabilities. [ABSTRACT FROM AUTHOR]

This paper comprehensively reviews sensors and sensing devices developed or/and proposed so far utilizing two smart materials: electrorheological fluids (ERFs) and magnetorheological materials (MRMs) whose rheological characteristics such as stiffness and damping can be controlled by external stimuli; an electrical voltage for ERFs and a magnetic field for MRMs, respectively. In this review article, the MRMs are classified into magnetorheological fluids (MRF), magnetorheological elastomers (MRE) and magnetorheological plastomers (MRP). To easily understand the history of sensing research using these two smart materials, the order of this review article is organized in a chronological manner of ERF sensors, MRF sensors, MRE sensors and MRP sensors. Among many sensors fabricated from each smart material, one or two sensors or sensing devices are adopted to discuss the sensing configuration, working principle and specifications such as accuracy and sensitivity. Some sensors adopted in this article include force sensors, tactile devices, strain sensors, wearable bending sensors, magnetometers, display devices and flux measurement sensors. After briefly describing what has been reviewed in a conclusion, several challenging future works, which should be undertaken for the practical applications of sensors or/and sensing devices, are discussed in terms of response time and new technologies integrating with artificial intelligence neural networks in which several parameters affecting the sensor signals can be precisely and optimally tuned. It is sure that this review article is very helpful to potential readers who are interested in creative sensors using not only the proposed smart materials but also different types of smart materials such as shape memory alloys and active polymers. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) represent an exceptional class of smart materials as they are able to recover their shape after mechanical deformation, making them suitable for use in actuators, sensors and smart devices. These unique properties are due to the thermoelastic martensitic transformation that can occur during both thermal and mechanical deformation. Cu-based SMAs, especially those incorporating Al and Ag, are attracting much attention due to their facile production and cost-effectiveness. Among them, Cu-Al-Ag SMAs stand out due to their notably high temperature range for martensitic transformation. In this study, a Cu-based SMA with a new ternary composition of Cu-10Al-7Ag wt.% was prepared by arc melting and the samples cut from this casting alloy were quenched in water. Subsequently, the phase composition and the development of the microstructure were investigated. In addition, the morphology of the martensite was studied using advanced techniques such as electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The analyzes confirmed the presence of martensitic structures in both samples; mainly 18R (β1′) martensite was present but a small volume fraction of (γ1′) martensite also was noticed in the as-quenched sample. The observation of fine, twinned martensite plates in the SMA alloy with symmetrically occurring basal plane traces between the twin variants underlines the inherent correlation between microstructural symmetry and the properties of the material and provides valuable insights into its behavior. The hardness of the quenched sample was found to be lower than the as-cast counterpart, which can be linked to the solutioning of Ag particles during the heat treatment. [ABSTRACT FROM AUTHOR]

The development of small-scale and low power consumption devices has been motivating the design of intelligent mechanisms, exhibiting a wide power density spectrum across various external sources. Smart materials come up as an attractive alternative due to their intrinsic multi-coupling between different physical domains. In this context, piezoelectric materials allow conversion of mechanical energy of movement into electrical power through the direct piezoelectric effect. This work investigates a piezoelectric energy harvester combined with a shape memory alloy (SMA) spring to explore the combination of both the smart materials for energy harvesting. The pseudoelastic hysteretic effect of SMA is explored in order to passively change the internal system properties such as stiffness and damping during the harvesting process. Numerical analyses are performed considering the normalized power converted by the harvester, focusing on the influence of the SMA martensite phase transformation under different scenarios. The results exhibit an increment in the harvester bandwidth when compared with a traditional linear piezoelectric energy harvester. [ABSTRACT FROM AUTHOR]

Featured Application: Superelastic shape memory alloy expansion joints are demonstrated as an alternative to traditional rubber expansion joints, with the potential for widespread application in bridge maintenance. In South Korea, the public infrastructure encompasses 172,111 facilities, with bridges accounting for a significant segment (totaling 34,199). These bridges undergo expansion due to traffic, vehicular loads, and temperature fluctuations. Expansion joint devices are installed to maintain vehicle stability and driving performance across expansion gaps. While these devices effectively ensure vehicular stability and performance, they do not address issues such as leakage and debris fall; therefore, rubber expansion joints should be installed. However, these rubber joints are prone to damage from various factors, resulting in secondary issues such as girder corrosion and accidents under bridges. Because of these inherent vulnerabilities, these joints require frequent replacements, making continuous bridge maintenance challenging. Therefore, this study explores the development of novel expansion joints using superelastic shape memory alloys to overcome the limitations of traditional rubber expansion joints. A comparative finite element analysis was conducted on the developed superelastic shape memory alloy and traditional rubber expansion joints. This study also assessed the long-term usability of these novel joints, particularly their ability to revert to their original shape post load removal. This research presents a promising alternative to conventional expansion joints and holds potential implications for enhancing the durability and safety of bridge infrastructure. [ABSTRACT FROM AUTHOR]

Biological species can walk, swim, fly, jump, and climb with fast response speeds and motion complexity. These remarkable functions are accomplished by means of soft actuation organisms, which are commonly composed of muscle tissue systems. To achieve the creation of their biomimetic artificial counterparts, various biomimetic stimuli-responsive materials have been synthesized and developed in recent decades. They can respond to various external stimuli in the form of structural or morphological transformations by actively or passively converting input energy into mechanical energy. They are the core element of soft actuators for typical smart devices like soft robots, artificial muscles, intelligent sensors and nanogenerators. Significant progress has been made in the development of bioinspired stimuli-responsive materials. However, these materials have not been comprehensively summarized with specific actuation mechanisms in the literature. In this review, we will discuss recent advances in biomimetic stimuli-responsive materials that are instrumental for soft actuators. Firstly, different stimuli-responsive principles for soft actuators are discussed, including fluidic, electrical, thermal, magnetic, light, and chemical stimuli. We further summarize the state-of-the-art stimuli-responsive materials for soft actuators and explore the advantages and disadvantages of using electroactive polymers, magnetic soft composites, photo-thermal responsive polymers, shape memory alloys and other responsive soft materials. Finally, we provide a critical outlook on the field of stimuli-responsive soft actuators and emphasize the challenges in the process of their implementation to various industries. [ABSTRACT FROM AUTHOR]

The growing demand for intelligent systems with improved human-machine interactions has created an opportunity to develop adaptive bending structures. Interactive fibre rubber composites (IFRCs) are created using smart materials as actuators to obtain any desired application using fibre-reinforced elastomer. Shape memory alloys (SMAs) play a prominent role in the smart material family and are being used for various applications. Their diverse applications are intended for commercial and research purposes, and the need to model and analyse these application-based structures to achieve their maximum potential is of utmost importance. Many material models have been developed to characterise the behaviour of SMAs. However, there are very few commercially developed finite element models that can predict their behaviour. One such model is the Souza and Auricchio (SA) SMA material model incorporated in ANSYS, with the ability to solve for both shape memory effect (SME) and superelasticity (SE) but with a limitation of considering pre-stretch for irregularly shaped geometries. In order to address this gap, Woodworth and Kaliske (WK) developed a phenomenological constitutive SMA material model, offering the flexibility to apply pre-stretches for SMA wires with irregular profiles. This study investigates the WK SMA material model, utilizing deformations observed in IFRC structures as a reference and validating them against simulated models using the SA SMA material model. This validation process is crucial in ensuring the reliability and accuracy of the WK model, thus enhancing confidence in its application for predictive analysis in SMA-based systems. [ABSTRACT FROM AUTHOR]

Active folding is a crucial requirement for practical applications of multi-stable origami structures. However, research on integrating active materials with origami structures to enable quick configuration switching and modulation of stability properties is still in its early stages. To advance the state-of-the-art, we designed a coupled structure comprising a stacked Miura-origami (SMO) structure and two Shape Memory Alloy (SMA) actuators. One actuator is used for extruding the SMO structure while the other is used for retracting, thereby realizing bidirectional reversible active folding of the coupled structure. Modeling the potential energy of the coupled structure shows that it can be switched between monostable and bistable by heating the SMA actuators. The above findings are also confirmed by experiments conducted on a delicate SMO-SMA coupled structure prototype. The activation of different actuators induces rapid configuration switching of the coupled structure, and the stability profile is qualitatively adjusted by designing the current loading profile to achieve steady-state temperature fluctuations. Overall, this study provides a new approach to coupling origami structures with smart materials for active folding and presents a novel method to regulate the stability property of origami structures, thus promoting their practical applications. [ABSTRACT FROM AUTHOR]

Smart materials are classified into several types such as piezoelectric materials, shape memory alloys (SMAs), magneto strictive materials, hydrogels, electroactive polymers, and bi-component fibers. SMAs exhibit the shape memory property of returning to their original shape after removing the load, and super elastic or pseudoplastic SMAs exhibit shape recovery behavior without thermal change. Currently, there is an interest in SMAs other than nitinol, such as Fe-SMAs and Cu-SMAs, in achieving shape memory applications due to the high processing cost of nitinol, and Cu-Al SMAs are one of the potential candidates. Alloy composition, manufacturing process, and post-processing are the principal characteristics of an SMA that must be controlled to achieve the mechanical, thermal, and chemical properties, microstructure, phase stability, and their application. Several studies report the fabrication, post-processing, and characterization of Cu-Al SMAs, but there is still a need to determine the methods that control the phase transformation behavior in terms of transformation temperatures to tailor these temperatures in the desired range. It should be noted that the martensitic transformation temperatures are a fundamental design aspect of Cu-Al SMAs, and it is essential to study the behavior of these smart materials particularly for civil and mechanical engineering technology students, as these alloys are promising for several innovative applications. [ABSTRACT FROM AUTHOR]

In extreme temperature environments, a newly emerging engineering application involves both the active and passive control of structures using cryogenic shape memory alloys, which are smart materials able to recover high deformation below the freezing point. With the objective of carrying out new advances in this area, the present work aims to investigate the Cu-7.5Al-13.5Mn (wt.%) shape memory alloy. Thermal, microstructural, and thermomechanical analyses of as-cast and hot-rolled specimens were performed, taking into account the effects of annealing and solubilization. It was observed that the phase transition occurs at temperatures below 120 K and changes according to the thermo-mechanical path. Specifically, hot-rolling lowers the phase transition temperature range with respect to the as-cast condition–from 34 K to 23 K for Mf, and from 89 K to 80 K for Af. Additionally, when the annealing temperature rises, the phase transformation temperature increases as well, and the alloy loses its cryogenic features when heat treated above 473 K. Finally, loss factors of 0.06 and 0.088, which were respectively found in dynamic and static settings, validate the material's good damping response. [ABSTRACT FROM AUTHOR]

A new functional Fe-30Mn-5Si-xCu (x = 1.5 and 2 wt%) biomaterial was obtained from the levitation induction melting process and evaluated as a biodegradable material. The degradation characteristics were assessed in vitro using immersion tests in simulated body fluid (SBF) at 37 ± 1 °C, evaluating mass loss, pH variation that occurred in the solution, open circuit potential (OCP), linear and cyclic potentiometry (LP and CP), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and nano-FTIR. To obtain plates as samples, the cast materials were thermo-mechanically processed by hot rolling. Dynamic mechanical analysis (DMA) was employed to evaluate the thermal properties of the smart material. Atomic force microscopy (AFM) was used to show the nanometric and microstructural changes during the hot rolling process and DMA solicitations. The type of corrosion identified was generalized corrosion, and over the first 3–5 days, an increase in mass was observed, caused by the compounds formed at the metal–solution interface. The formed compounds were identified mainly as oxides that passed into the immersion liquid. The degradation rate (DR) was obtained as a function of mass loss, sample surface area and immersion duration. The dynamic mechanical behavior and dimensions of the sample were evaluated after 14 days of immersion. The nanocompounds found on the surface after atmospheric corrosion and immersion in SBF were investigated with the Neaspec system using the nano-FTIR technique. [ABSTRACT FROM AUTHOR]

The replication of jumping motions observed in small organisms poses a significant challenge due to size‐related effects. Shape memory alloys (SMAs) exhibit a superior work‐to‐weight ratio, making them suitable for jumping actuators. However, the SMAs advantages are hindered by the limitations imposed by their single actuator configuration and slow response speed. This study proposes a novel design approach for an insect‐scale shape memory alloy jumper (net‐shell) using 4D printing technology and the bistable power amplification mechanism. The energy variations of the SMA net‐shell under different states and loads are qualitatively elucidated through a spring‐mass model. To optimize the performance of the SMA net‐shell, a non‐contact photo‐driven technique is employed to induce its shape transition. Experimental investigations explore the deformation response, energy release of the net‐shell, and the relationship between the light power density. The results demonstrate that the SMA net‐shell exhibits remarkable jumping capabilities, achieving a jump height of 60 body lengths and takeoff speeds of up to 300 body lengths per second. Furthermore, two illustrative cases highlight the potential of net‐shells for applications in unstructured terrains. This research contributes to miniaturized jumping mechanisms by providing a new design approach integrating smart materials and advanced structures. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the dynamic properties of new structures formed by combining carbon fiber and epoxy resin-based composite materials with SMA (shape memory alloy) "smart materials" in the form of NiTiNol wire. Such a combination will have an impact on the dynamics of the structure, especially in terms of stiffness controllability. Key mechanical parameters such as natural frequency and stiffness, as well as the effect of temperature, were determined through experimental studies. [ABSTRACT FROM AUTHOR]

In recent years, there has been a renewed interest in kinetic systems made with smart materials that can adapt to changing environmental conditions. This paper describes design research to develop and improve the design of a holder unit that is the basic component of a kinetic bistable shading system. The holder comprises four bistable flaps and linear actuators with shape memory alloy (SMA) springs. The linear actuators force the bistable flaps to snap into their opened and closed positions. Two experimental studies were conducted: (1) a study to find an adequate SMA and biasing springs combination for a linear actuator; and (2) a shape optimization study. The first study aimed to find an adequate configuration for the linear actuator, which has both SMA and biasing springs. In the study, data obtained by image analysis were analyzed statistically to understand which combination of SMA and biasing springs resulted in the largest displacement. The second study used topology optimization to obtain a 25% reduction in the total volume of the holder unit compared to the initial design, resulting in a lighter kinetic structure. The paper describes the two studies conducted, highlighting the resulting improvements in the holder unit for the kinetic screen. [ABSTRACT FROM AUTHOR]

Magnetic shape memory alloys are emerging multifunctional materials that enable applications like high-stroke actuation, solid-state refrigeration, and energy harvesting of waste heat. Thin films of these alloys promise integration in microsystems to exploit their multifunctional properties at the microscale. However, the microfabrication process of these Heusler alloys is difficult. Herein, different etching techniques are investigated for the microfabrication of epitaxial Ni-Mn-Ga films, the encountered challenges are explained, and ways to overcome them are demonstrated. The results show that wet chemical etching is suitable for large patterned structures, while reactive ion etching of Ni-Mn-Ga films is unsuitable due to redeposition. For patterning structures below 10 μm with clean and sharp edges, the best results are obtained by ion beam etching with adjusted sample-stage tilt. Finally, a microfabrication process using Si microtechnology to fabricate partially freestanding structures is demonstrated. These findings give guidelines for the fabrication and integration of these smart materials in Si-based microsystems. [ABSTRACT FROM AUTHOR]

Thanks to the use of modern intelligent materials, such as composites consisting of piezoceramic fibers embedded in epoxy resin and covered with alternating electrodes, electroactive polymers, dielectric elastomers, magnetostrictive composites with epoxy resin or ferromagnetic alloys with shape memory, it is possible to control the geometry or properties of materials using pressure, external magnetic or electric fields. The paper analyzes multilayer quasi-one-dimensional phononic structures in which the selected layer is made of a material with time-varying acoustic impedance. The influence of the shape of the material properties changes over time (square wave, triangle wave, sawtooth wave) on the propagation of mechanical waves in the structure is analyzed. [ABSTRACT FROM AUTHOR]

This study reviews the recent works on the development and application of iron‐based shape memory alloy (Fe‐SMA), the so‐called memory‐steel, for steel structures. First, the studies on the material properties of Fe‐SMA in terms of shape memory effect and superelasticity are discussed. Next, the use of Fe‐SMA in prestressed strengthening of steel structures is explained, including the applications in strengthening of steel girders, connections, and fatigue crack repairs. Various strengthening solutions such as using mechanically anchored or adhesively‐bonded Fe‐SMA, as well as the studies on the behavior of the Fe‐SMA‐to‐steel bonded joints, are discussed. The use and application of Fe‐SMA for strengthening of a 113‐years steel bridge has been explained. In addition, studies on the innovative application of the Fe‐SMA as pipe couplers are presented. At the end, innovative ongoing research on the additive manufacturing of architected Fe‐SMA (4D‐printing) are discussed. [ABSTRACT FROM AUTHOR]

Shape memory effects coupled with superelasticity are the distinctive characteristics of shape memory alloys (SMAs), a type of metal. When these alloys are subject to thermomechanical processing, they have the inherent ability to react to stimuli, such as heat. As a result, these alloys have established their usefulness in a variety of fields and have in recent years been chosen for use in stents, sensors, actuators, and several other forms of life-saving medical equipment. When it comes to the shape memory materials, nickel–titanium (Ni-Ti) alloys are in the forefront and have been chosen for use in a spectrum of demanding applications. As shape memory alloys (SMAs) are chosen for use in critical environments, such as blood streams (arteries and veins), orthodontic applications, orthopedic implants, and high temperature surroundings, such as actuators in aircraft engines, the phenomenon of environment-induced degradation is of both interest and concern. Hence, the environment-induced degradation behavior of the shape memory alloys (SMAs) needs to be studied to find viable ways to improve their resistance to an aggressive environment. The degradation that occurs upon exposure to an aggressive environment is often referred to as corrosion. Environment-induced degradation, or corrosion, being an unavoidable factor, certain techniques can be used for the purpose of enhancing the degradation resistance of shape memory alloys (SMAs). In this paper, we present and discuss the specific role of microstructure and contribution of environment to the degradation behavior of shape memory alloys (SMAs) while concurrently providing methods to resist both the development and growth of the degradation caused by the environment. [ABSTRACT FROM AUTHOR]

Textiles composed of fibers can have their mechanical properties adjusted by changing the arrangement of the fibers, such as strength and flexibility. Particularly, in the case of smart textiles incorporating active materials, various deformations could be created based on fiber patterns that determine the directivity of active materials. In this study, we design a smart fiber-based textile actuator with a chain structure and evaluate its actuation characteristics. Smart fiber composed of shape memory alloy (SMA) generates deformation when the electric current is applied, causing the phase transformation of SMA. We fabricated the smart chain column and evaluated its actuating mechanism based on the size of the chain and the number of rows. In addition, a crochet textile actuator was designed using interlooping smart chains and developed into a soft gripper that can grab objects. With experimental verifications, this study provides an investigation of the relationship between the chain actuator's deformation, actuating force, actuator temperature, and strain. The results of this study are expected to be relevant to textile applications, wearable devices, and other technical fields that require coordination with the human body. Additionally, it is expected that it can be utilized to configure a system capable of flexible operation by combining rigid elements such as batteries and sensors with textiles. [ABSTRACT FROM AUTHOR]

In recent years, there has been a significant demand for shape memory materials due to their smart characteristics. NiMnGa has special interest because of its magnetic shape memory features which can be used in actuators, sensors, dampers, and energy harvesting. The production of NiMnGa has a substantial cost resulting in usage of a shape memory polymer composite with the alloy which brings advantages such as size, and shape structure. For this purpose, a new multifunctional smart material was studied by combining Poly lactic acid (PLA)/Poly ethylene glycol (PEG) blend obtained with Ni49.5Mn29.5Ga21 (in % atomic). Different ratios of the alloy were doped into the blend to investigate the effect of the alloy on the characteristic features of the composite. Physicochemical properties of NiMnGa enriched composites were analyzed by attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). From DSC analysis it is concluded that the magnetically enhanced PLA/PEG films with the alloy had two important phase transformations. Although NiMnGa shape memory alloy did not affect the initial decomposition temperature (Ti) of the PLA/PEG blend much, the residue ratio increased with increasing alloy content. The characteristic XRD signal of the alloy becomes observable with the increasing amount of NiMnGa in the composite. In addition, the diamagnetic PLA/PEG blend gained magnetic properties with addition of the alloy. It is also observed that NiMnGa had a positive effect on the shape memory feature of the polymer blend. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) are currently one of the most attractive smart materials expected to replace traditional shape memory alloys and ceramics (SMAs and SMCs, respectively) in some fields because of their unique properties of high deformability, low density, easy processing, and low cost. As one of the most popular SMPs, shape memory polyurethane (SMPU) has received extensive attention in the fields of biomedicine and smart textiles due to its biocompatibility and adjustable thermal transition temperature. However, its laborious synthesis, limitation to thermal response, poor conductivity, and low modulus limit its wider application. In this work, biocompatible poly(ε-caprolactone) diol (PCL-2OH) is used as the soft segment, isophorone diisocyanate (IPDI) is used as the hard segment, and glycerol (GL) is used as the crosslinking agent to prepare thermoset SMPU with a thermal transition temperature close to body temperature for convenient medical applications. The effects of different soft-chain molecular weights and crosslinking densities on the SMPU's properties are studied. It is determined that the SMPU has the best comprehensive performance when the molar ratio of IPDI:PCL-2OH:GL is 2:1.5:0.33, which can trigger shape memory recovery at body temperature and maintain 450% recoverable strain. Such materials are excellent candidates for medical devices and can make great contributions to human health. [ABSTRACT FROM AUTHOR]

This review paper deals with the advancements of composites to shape memory alloys. The journey of smart materials from conventional composites to advance shape memory alloys and their application is described in this literature. Classification of smart materials such as smart composites, shape memory alloys, polymer composite and various other types of materials that are intelligent are explained briefly. Different manufacturing and developing techniques to manufacture smart materials and characterization of conventional composites is compared with advance modern day shape memory alloys. Shape memory effect such as one way and two-way shape memory effect are depicted. However, the most important of all the applications and extensive use of smart materials in health care sector for implants and various other uses with uses in aerospace and automotive industries are reviewed.

Nickel-Titanium (Ni-Ti) is an intermetallic alloy that has exhibited a unique ability to recover its original shape after deformation, and this ability is well known as the so-called shape memory effect. On the other hand, with the special behavior of pseudoelastic/superelasticity, Ni-Ti shape memory alloys (SMAs) also draw widespread attention in a wide range of engineering fields. Ni-Ti SMAs used to be considered as some kind of smart materials due to the shape memory effect and pseudoelastic/superelasticity performance. However, Ni-Ti SMAs have attracted increasing interest in tribological applications over the past two decades owing to their excellent wear resistance, which is mainly ascribed to their pseudoelasticity. On account of this point, Ni-Ti alloys have also been chosen as surface strengthening materials to improve the wear performance of various substrates using different surface technologies. From the view of process selection and performance estimation, this review suggests the research progress of preparation and application of Ni-Ti alloys as strengthening material. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are smart materials with unique properties of superelasticity and shape memory effect. These properties are the consequence of thermoelastic martensitic transformation, which can occur under thermal or mechanical deformation. Cu-Al-Ag alloys have high temperatures of martensite transformation, unlike other SMAs, which makes them suitable for use in specific applications. In this paper, Cu- 10Al-1Ag alloy was prepared by melting pure metals in an electric arc furnace and casting the melt in a cylindrical mold. The microstructure of the as-cast and quenched material was determined by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive analysis (EDS). X-ray diffraction (XRD) analysis was performed to identify crystal phases in the microstructure, while transformation temperatures were determined by differential scanning calorimetry (DSC). The hardness of Cu-Al-Ag SMA was also determined with a microhardness tester. The results showed partially formed martensite in the as-cast state, and fully formed martensite structure, 18R-type, in the quenched Cu-10Al-1Ag alloy. [ABSTRACT FROM AUTHOR]

Upgraded design standards coupled with the damage caused by natural disasters have led to the development of smart materials with the potential to modernize current construction practices. This investigation proposes a nonlinear finite element (FE) model for evaluating the performance of beam–column joints (RC-BCJ) reinforced with shape memory alloys (SMA) and steel rebars. The model was validated based on accredited experimental data, followed by parametric analysis in ABAQUS to optimize the use of SMA bars for enhancing the seismic resistance of RC-BCJ without compromising their energy dissipation capacity. Parameters investigated include the (a) SMA–steel reinforcement ratio, (b) lengths of SMA bars, (c) elastic modulus of SMA, (d) compressive strength of concrete, and (e) axial load applied on the column. The finite element simulation results indicated that the model was capable of predicting the optimum length of SMA bars sufficient for relocating the plastic hinge away from the face of the column along the beam. Further, simulation results proved that the use of SMA bars in conjunction with steel reinforcement could be considered as an effective tool for enhancing the seismic performance of RC-BCJ joints. Among the parameters investigated, high-strength concrete was the most effective in improving joint resistance. [ABSTRACT FROM AUTHOR]

Space debris is considered an increasingly serious threat to on‐orbit spacecrafts. There are several potential solutions to this problem, including active debris removal. Flexible robots have shown promising adaptability and dexterity in soft manipulation owing to their inherent compliance. This compliance allows them to interact safely and efficiently during space missions such as active debris removal. Herein, inspired by the bistable structure and energy‐release mechanism of the Venus flytrap, a bistable origami‐based gripper is developed. The flexible gripper, which can rapidly achieve stable state switching, is in the form of a biomimetic flytrap leaf curvature and is actuated using a shape memory alloy actuator. Subsequently, a flytrap bristle‐like locking structure is used to ensure locking via the action of a dielectric elastomer actuator to alleviate the vibration instability of the flexible robot under rapid actuation. The experimental results showed that the flexible gripper can achieve effective capture within approximately 300 ms. In addition, it exhibits good adaptability and mechanical robustness with targets having complex shapes and sizes, indicating its potential applications in the space capture and sampling fields. [ABSTRACT FROM AUTHOR]

Recent advances in materials science have led to the development of smart materials that can continuously adapt to different loading conditions and changing environment to meet the growing demand for smart structural systems. The unique characteristics of superelastic NiTi shape memory alloys (SMAs) have attracted the attention of structural engineers worldwide. SMAs are metallic materials that can retrieve their original shape upon exposure to various temperatures or loading/unloading conditions with minimal residual deformation. SMAs have found increasing applications in the building industry because of their high strength, high actuation and damping capacities, good durability, and superior fatigue resistance. Despite the research conducted on the structural applications of SMAs during the previous decades, the existing literature lacks reviews on their recent uses in building industry such as prestressing concrete beams, seismic strengthening of footing–column connections, and fiber-reinforced concrete. Furthermore, scarce research exists on their performance under corrosive environments, elevated temperatures, and intensive fires. Moreover, the high manufacturing cost of SMA and the lack of knowledge transfer from research to practice are the main obstacles behind their limited use in concrete structures. This paper sheds light on the latest progress made in the applications of SMA in reinforced concrete structures during the last two decades. In addition, the paper concludes with the recommendations and future opportunities associated with expanding the use of SMA in civil infrastructures. [ABSTRACT FROM AUTHOR]