Shape Memory Research Articles

Machine learning insights into the strain-stress behavior of nitinol alloys at low temperatures: Utilizing the orange data mining tool

This study entails a new technique, based on machine learning algorithms, for predicting the strain-stress behavior of Nitinol alloys. The study utilizes Orange data mining software to determine if algorithms like Linear Regression, Random Forest, k-nearest neighbors, and decision tree are related to the effectiveness. The nitinol-based alloy, which has both shape memory and superelasticity, is used in a wide range of biomedical devices, aerospace constructions, and automated apparatus. Temperature variation is a main factor affecting the Nitinol behavior. It is therefore required to carry out an in-depth analysis of strain-stress patterns. Employing machine learning algorithms along with data mining tools allows the exact prediction of the Nitinol alloy performance under any given condition. The research is purposed to establish the relationship between temperature and mechanical strength of Nitinol by analyzing strain-stress curves that were obtained from tensile tests carried out at different temperatures. Looking at overall results, kNN has the highest accuracy of the models upon comparing MSE and RMSE, and has higher R² and, therefore stands as the model of high reliability. Results show that machine learning algorithms successfully forecast the mechanical responses of Nitinol under temperature variations, which assists in determining their formability properties and hence, advancing Nitinol applications in various fields. This research demonstrates machine learning uses in developing materials science and engineering knowledge by showing the ability to predict Nitinol alloy behavior, which includes strain-stress characteristics at low temperatures. Furthermore, the research's significance lies in addressing ethical considerations and practical issues, such as the necessity of implementing an organized approach to achieve environmental benefits.

Novel sustainable, smart, and multifunctional 4D-printed nanocomposites with reprocessing and shape memory capabilities

Abstract The present paper explores the development of novel recyclable and reprocessable nanocomposites with enhanced shape memory (SM) capability Digital Light Processing 3D printing technology. More specifically, the developed Covalent Adaptable Network is based on polyurethane containing Diels Alder bonds reinforced with carbon nanotubes (CNTs), where the dynamic bonds enable recyclability and reprocessability, whereas CNT addition allows obtaining electrically conductive nanocomposites. In this sense, the nanocomposites exhibited significant Joule heating capabilities, which were used to trigger the SM cycle.
First, CNT contents and thermal treatments were tuned to optimize SM capabilities in a conventional oven, seeking for obtaining a stable temporary shape at room temperature. Then, the SM capabilities triggered by Joule heating were characterized. Here, the optimized nanocomposites showed excellent shape fixity and recovery ratios (both above 95 %) when triggering the SM by the Joule effect. This heating method was proven to be low energy-consuming (around 1 W), as well as allowing fast, remote, and selective activation, being the latter the ability to trigger the SM in a specific area of the specimen as desired, which was demonstrated with a hand-like proof-of-concept by selectively recovering the permanent shape of each finger.
Finally, the 3D-printed specimens were turned into powder and reprocessed using a powder processing tool, obtaining a still electrically conductive part with a different geometry given the DA adduct formations.
In summary, the multifunctional and smart capabilities of the developed nanocomposites make them suitable for applications such as soft robotics or actuators with an extended useful life, promoting sustainability.

Robust Mechanically Interlocked Network Ionogels.

Ionogels have attracted considerable attention as versatile materials due to their unique ionic conductivity and thermal stability. However, relatively weak mechanical performance of many existing ionogels has hindered their broader application. Herein, we develop robust, tough, and impact-resistant mechanically interlocked network ionogels (IGMINs) by incorporating ion liquids with mechanical bonds that can dissipate energy while maintain structural stability. Profiting from the dynamic yet stable nature of the mechanically interlocked networks, IGMINs exhibit high tensile strength (9.6 MPa), fracture energy (39 kJ/m2), and toughness (25.9 MJ/m3), along with a high elongation rate (473%) and excellent impact resistance and shape memory, resulting in overall performance that surpasses most reported ionogels. Furthermore, in the application of strain sensors for monitoring the gait of crawling robots, the toughness and robustness of IGMINs ensure their ability to consistently output stable electrical signals during the stretching and contraction processes, thereby highlighting their practical application potential. Our work provides a new research strategy for toughening ionogels and promotes the development of mechanically interlocked materials.

Computer simulations of entropic cohesion in reversibly crosslinked polymers.

Reversibly crosslinked polymer networks - polymer networks that can undergo bond association and dissociation reactions - rearrange their structures while maintaining their overall integrity, thus resulting in unique properties such as self-healing, reprocessability, shape memory and adaptability. Here, we show that the introduction of crosslinks, whether reversible or permanent, directly impacts the equilibrium polymer density and hence the material's surface tension. For a limiting case where the bonds are the same size as the polymer chain bonds, simulations, Flory hypotheses and thermodynamic calculations show that the crosslinks induce an increased entropic cohesion in the liquid. These findings implicate density as a key variable in polymers with (dynamic) crosslinkers, one that can be used to facilely tune their properties.

Knowledge-enabled data-driven smart design advanced high-entropy alloys with attractive dynamic mechanical properties

Knowledge-enabled data-driven smart design advanced high-entropy alloys with attractive dynamic mechanical properties

Electroconductive Nanocellulose, a Versatile Hydrogel Platform: From Preparation to Biomedical Engineering Applications.

Nanocelluloses have garnered significant attention recently in the attempt to create sustainable, improved functional materials. Nanocellulose possesses wide varieties, including rod-shaped crystalline cellulose nanocrystals and elongated cellulose nanofibers, also known as microfibrillated cellulose. In recent times, nanocellulose has sparked research into a wide range of biomedical applications, which vary from developing 3D printed hydrogel to preparing structures with tunable characteristics. Owing to its multifunctional properties, different categories of nanocellulose, such as cellulose nanocrystals, cellulose nanofibers, and bacterial nanocellulose, as well as their unique properties are discussed here. Here, different methods of nanocellulose-based hydrogel preparation are covered, which include 3D printing and crosslinking methods. Subsequently, advanced nanocellulose-hydrogels addressing conductivity, shape memory, adhesion, and structural color are highlighted. Finally, the application of nanocellulose-based hydrogel in biomedical applications is explored here. In summary, numerous perspectives on novel approaches based on nanocellulose-based research are presented here.

Utilization of a smart TiCo alloy for pressure-induced hydrogen storage

Abstract One of the most important challenges facing countries is providing cheap energy and renewable sources. Therefore, a smart alloy will be proposed for hydrogen storage due to its ability to expand and contract without breaking and being little affected by heat. In this investigation, the first performance principle is applied to examine the effect and utility of hydrogen absorption in smart TiCo alloy. The hydrogen atoms absorbed at the bridge (TiCoH3-B), face-centered cubic (TiCoH3) and tetrahedral interstitial (TiCoH8) sites in TiCo alloy were studied. The elastic constants, enthalpy of formation energy, and tolerance factors show that TiCoH3 and TiCoH8 are stable alloys and can be formed, while TiCoH3-B is not elastically stable. Cohesive energy shows that increasing induced pressure and hydrogen absorption reduces the stiffness of TiCoH3 and TiCoH8, without alloy collapse. The gravimetric storage capacity of CoTiH3 and TiCoH8 is found to be large enough to be suitable as alloys for hydrogen storage. Pugh’s B/G ratio, and anisotropy factor assume that TiCo with or without hydrogen atoms is classified as a ductile and anisotropic alloy, with except for TiCoH8 has brittle behavior up to 40 GPa. The bonding nature of TiCoH3 alloy has a mixture of covalent (Co – H) and ionic bond (CoH6 – Ti). In contrast, TiCoH8 exhibits a covalent bond in the form of Ti – H – Co. Hydrogen absorption and induced pressure encourage electrons to rearrange into the spin up and down channels resulting in a decrease in the overall magnetic moment of the alloy. The mechanical, electronic, and magnetic properties show promise for industrial applications of these alloys, such as piezoelectric and hydrogen storage, and spin and magnetoelectronic manufacturing.

Shape Memory and Superelasticity Announces New Additions to the Editorial Advisory Board

Shape Memory and Superelasticity Announces New Additions to the Editorial Advisory Board

Programable shape recovery properties and snap-through instabilities of viscoelastic and shape-memory NS metamaterials

The combination of smart material and mechanical metamaterial has the potential to bring novel properties and additional functionalities, which, however, has been ignored for a long time. This work numerically, experimentally, and analytically examines the negative stiffness (NS) metamaterials based on shape memory polymers (SMPs) with a focus on the tunable and temperature-dependent properties induced by the interaction of material and geometry nonlinearity. A universal discrete model of a series of shape-memory NS metamaterial is developed by separating the bending effect and stretching effect, where the viscoelastic material is described by the generalized Maxwell-Wiechert model, and an SMP constitutive model is proposed based on multiplicative decomposition of the deformation gradient. The mechanical and shape-memory properties influenced by temperature, geometry, material and loading rate are experimentally observed through relaxation tests and cyclic compression tests. Then the discrete model and finite element analysis (FEA) is adopted to examine the novel mechanical responses in a wide range of parameters. Results show that viscoelasticity and loading rate play a significant role in mechanical responses, and tunable load-capacity and stability can be achieved for shape-memory metamaterial. A phase diagram of different stabilities is constructed showing strictly monotonic, S-shaped, and snapping responses. Additionally, repeated compression and recovery performance proves the possibility of reusable applications. This work provides new opportunities for functional metamaterial to obtain programmable shape recovery and mechanical responses.

Electrodeposition of Sacrificial Layer, Al2O3/ZnTPP film, onto NiTi Orthodontic Wire: Surface Characterizations and Electrochemical Investigations

Background: NiTi (nickel-titanium) alloy wires are widely used in orthodontics due to their unique properties, such as shape memory and superelasticity. However, these wires can be susceptible to corrosion in the oral environment, which can compromise their mechanical performance and longevity. Zinc tetraphenyl porphyrin (ZnTPP) is a corrosion inhibitor that forms a protective layer on the aluminum oxide (Al2O3) surface, acting as a barrier against corrosive agents. Objective: The electrodeposition of a sacrificial layer of Al2O3 with ZnTPP was carried out onto Ni- Ti orthodontic wire to enhance the corrosion resistance. Methods: 10 mM aluminum nitrate was dissolved in 10 mL of 0.1 M phosphate buffer solution (PBS), which was used as an electrolyte. Firstly, electrodeposition of Al2O3 on NiTi wire was carried out by using cyclic voltammetry by potential scanning between 0 and -2.0 V at a scan rate of 50 mV/s for 50 cycles. Secondly, 10 mL of 1 mM ZnTPP in 0.1 M PBS and ethanol (1:1) was prepared and used as an electrolyte. Electrodeposition of ZnTPP onto Al2O3/NiTi wire was achieved by cyclic voltammetry through the potential window of 0 to -2.0 V at a scan rate of 50 mV/s for 50 cycles. Results: The ZnTPP/Al2O3/NiTi wire displayed a potentiodynamic polarization resistance of 412931 Ω, with high stability compared to the bare NiTi wire (396421 Ω). Additionally, the corrosion rate for the ZnTPP/Al2O3/NiTi wire was measured as 0.254 mm/year, which was notably lower than that of the bare NiTi wire (0.540 mm/year). This decrease in corrosion rate can be attributed to the presence of the ZnTPP/Al2O3 film, which renders the NiTi wire electrically insulative and significantly increases its impedance compared to the bare NiTi wire. Conclusion: The bilayer coating of Al2O3 and ZnTPP has proven to significantly improve the corrosion resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic archwires with improved corrosion stability.

Mechanics‐Photophysics Correlation in Tough, Stretchable and Long‐Lived Room Temperature Phosphorescence Ionogels Deciphered by Dynamic Mechanical Analysis

AbstractThe development of tough, stretchable and long‐lived room temperature phosphorescence (RTP) materials holds great significance for manufacturing and processing photoluminescent materials, but limited techniques are available to profile their mechanics‐photophysics correlation. Here we report glassy ionogels, and their mechanical properties and photophysical properties are fused by dynamic mechanical analysis (DMA), functioning like a human brain that perceives a material instantaneously by linking sensory perception and cognition. Depending on two special temperatures presented in DMA curves, Tloss (the peak of loss modulus (E”)) and Tg (glass transition temperature), the ionogels can vary from being either tough with persistent phosphorescence, extensible with effective phosphorescence or resilience with inefficient phosphorescence. Leveraging this method, we achieve stretchable and long‐lived RTP ionogels with tensile yield strength of 53 MPa, tensile strain of 497 %, Young's modulus of 782 MPa, toughness of 111.2 MJ/m3, and lifetime of 113.05 ms. Our work provides a simple yet powerful method to reveal the mechanics‐photophysics correlation of RTP ionogels, to predict their performance without laborious synthesis and characterization, opening new avenues for applications of RTP materials, including applications in harsh conditions (257 K or 347 K), shape memory and shape reconstruction.

Mechanics-Photophysics Correlation in Tough, Stretchable and Long-Lived Room Temperature Phosphorescence Ionogels Deciphered by Dynamic Mechanical Analysis.

The development of tough, stretchable and long-lived room temperature phosphorescence (RTP) materials holds great significance for manufacturing and processing photoluminescent materials, but limited techniques are available to profile their mechanics-photophysics correlation. Here we report glassy ionogels, and their mechanical properties and photophysical properties are fused by dynamic mechanical analysis (DMA), functioning like a human brain that perceives a material instantaneously by linking sensory perception and cognition. Depending on two special temperatures presented in DMA curves, Tloss (the peak of loss modulus (E")) and Tg (glass transition temperature), the ionogels can vary from being either tough with persistent phosphorescence, extensible with effective phosphorescence or resilience with inefficient phosphorescence. Leveraging this method, we achieve stretchable and long-lived RTP ionogels with tensile yield strength of 53 MPa, tensile strain of 497 %, Young's modulus of 782 MPa, toughness of 111.2 MJ/m3, and lifetime of 113.05 ms. Our work provides a simple yet powerful method to reveal the mechanics-photophysics correlation of RTP ionogels, to predict their performance without laborious synthesis and characterization, opening new avenues for applications of RTP materials, including applications in harsh conditions (257 K or 347 K), shape memory and shape reconstruction.

A Bistate Intelligent Eutectogel Material with Water‐Regulated Stiffness for Diverse Designed Functionality

AbstractThe design of stiffness‐changeable synthetic materials that can mimic their biological counterparts in the production of adaptable structures and functions is highly important but remains challenging. Here, the development of a bioinspired intelligent material composed of a deep eutectic solvent (DES) and an ionically crosslinked polymer network that is capable of switching reversibly between hard plastic and soft elastic states in response to water is reported. The eutectogel stiffness can be dramatically switched and flexibly regulated by water, which can activate salt ionization and shield the ionic crosslink. This design principle is extensively applied to multiple polymers, producing a series of bistate materials that exhibit water‐regulated capabilities ranging from self‐healing, shape memory, remolding, antifreezing, anticompressing, and stretchability to conductivity. These bistate materials are used for diverse functions, such as performing mechanical tasks, sensing and monitoring human movements, lighting LEDs, and outputting signals. This work opens an avenue for the development of next‐generation stiffness‐changeable materials with diverse functionalities for various designed applications.

A Review of Polyurethane Foams for Multi-Functional and High-Performance Applications.

Polyurethane (PU) foams are cellular polymeric materials that have attracted much attention across various industries because of their versatile properties and potential for multifunctional applications. PU foams are involved in many innovations, especially in multi-functional and high-performance applications. Special attention is given to developing tailored PU foams for specific application needs. These foams have various applications including flame retardancy, sound absorption, radar absorption, EMI shielding, shape memory, and biomedical applications. The increasing demand for materials that can perform multiple functions while maintaining or enhancing their core properties has made PU foams a focal point of interest for engineers and researchers. This paper examines the challenges faced by the PU foam industry, particularly in developing multifunctional products, as well as the strategies for improving sustainability, such as producing PU foams from renewable resources and recycling existing materials.

Recent Advances in Smart Emulsion Materials: From Synthesis to Applications

Smart emulsions are both versatile additives to smart materials and functional smart materials themselves, acting as active components and structural elements driving innovative development. Emulsions offer versatility, ease of manipulation, and stability to smart materials. This review explores the multifaceted roles of emulsions, examining their formulation methods, applications, and role as building blocks in smart materials. The significance of emulsions in smart materials is discussed for applications such as drug delivery and adaptive coatings, as well as their role in stimuli‐responsive colloidal systems and nanocomposites. The smart emulsions reviewed encompass all manner of material types, including fluid and solid/polymerized smart materials. These include both emulsions with dynamic properties and emulsions used in the process of synthesizing other materials. Smart emulsions are categorized by application into shape memory, self‐healing, biological, and stimuli‐responsive, with analysis of formulation methods, metrics, and methods of final incorporation. Smart emulsions can be found initially as fluid systems and some react into solid polymers, tailored to meet functional needs. A comparative analysis reveals emerging trends such as coupling coating self‐healing/corrosion inhibition and use of waterborne polyurethanes. The discussion of smart emulsions concludes by outlining challenges and future directions for leveraging smart emulsions.

Investigating Melt Pool Dimensions in Laser Powder Bed Fusion of Nitinol: An Analytical Approach

Nitinol (NiTi) has gained popularity across various industries due to its shape memory and superelastic properties. Recently, additive manufacturing (AM) has been increasingly utilized to produce NiTi components. This study focuses on single‐track nitinol samples fabricated via powder bed fusion using laser beam (PBF‐LB). Investigating the effects of laser power and scanning speed on melt pool dimensions reveals that melt pool width increases linearly with laser power and decreases logarithmically with scanning speed. However, melt pool depth exhibits outliers that deviate from these trends. Three analytical models are evaluated to predict melt pool dimensions, generally aligning with experimental trends. Notably, the Eagar–Tsai model delivers the most accurate predictions for melt pool width, with a mean absolute error of less than 10%, while the Gladush–Smurov model is more reliable for melt pool depth predictions, showing a mean absolute error under 20%. In contrast, the Rosenthal equation yields less reliable results for both dimensions. This suggests that a combined approach utilizing the strengths of both the Eagar–Tsai and Gladush–Smurov models may provide the most accurate predictions for the melt pool profile of NiTi in PBF‐LB.

Thin-film electrodes of dielectric elastomer-based actuators for an active vibration control system

Precision research and technological equipment, as a rule, is not able to provide its specification characteristics without a high-quality vibration protection system. Active vibration control of an object is provided with the help of an additional source of movement, an actuator. The most promising high accuracy actuators are based on smart materials, such as materials with shape memory, piezoelectric and magnetostrictive materials, electro- and magnetic active fluids and elastomers. Dielectric elastomer is one of the types of electroactive polymers. Actuators based on a dielectric elastomer show high performance in terms of accuracy and speed and operate due to the controllable deformation of the elastomer under the action of a high voltage electric field. The paper provides a comparison of actuators based on sheet and thin film control electrodes. The influence of the quality of the polymer surface and the type of electrodes on the travel range of the actuator and maximum amplitude of vibrations the system can suppress on the basis of a dielectric elastomer is estimated. The formation of the electrode by magnetron sputtering in vacuum makes it possible to create a thin-film layer of copper that covers the elastomer, despite the developed surface. The effect of ion treatment of an elastomer before coating on the quality of the formed electrode is considered. After the ion treatment, the surface of the elastomer acquires a more uniform regular structure. A thin-film electrode layer is formed according to the topology of the elastomer to an accomplished standard.

The Effect of Intraoral Thermal Changes on the Mechanical Behavior of Nickel-Titanium Wires: An In-Vitro Study.

Background The continuous light force with a wide range of activation describes the excellent properties of nickel-titanium (NiTi) archwires. Shape memory is mainly affected by intraoral thermal changes. This study evaluated the effect of three different constant temperatures (i.e., 12°C, 37°C, and 50°C) on the unloading value of three different 0.016 × 0.022 NiTi archwires. Methodology Three types of 0.016 × 0.022-inch diameter NiTi archwires (American Orthodontics®, Sheboygan, Wisconsin, USA) were used. These were the superelastic type (NT3-SE®), the heat-activated type at 25°C (Thermal Ti-D®), and the thermally activated type at 35°C (Thermal Ti-Lite®). The unloading forces of the wires were evaluated using a classic three-point bending test (a universal testing machine: Testometric 350M®, Instron, Lincoln Close, Rochdale, England) under three different constant temperatures (12°C, 37°C, and 50°C). Results All types of wires showed thermal sensitivity; at higher temperatures, the unloading forces increased differentially between small and large deflections, while at lower temperatures, the residual strain increased for all wire types. The most affected type by the thermal changes was thermal Ti-Lite®, followed by thermal Ti-D®, and the superelastic type NT3-SE® showed a behavior similar to thermal wires. At the low temperature (12°C), all wire types showed an incomplete load/deflection curve, whereas no value was measured at unloading points 2, 1, and 0.5 mm. At the normal temperature (37°C), NT3-SE® type and thermal Ti-D® were similar in force level, while significant differences were noted between both previous types and Thermal Ti-Lite®. At the high temperature (50°C), all wire types showed a higher force level, while significant differences between the wire types were inconsistent. In contrast, increasing the temperature from 37°C to 50°C increased the force levels between 40% and 84% for NT3-SE®, between 44% and 64% for the thermal Ti-D®, and between 61% and 268% for the Thermal Ti-Lite®. When comparing the force levels between 12°C and 50°C at 3 mm, the force levels increased by 66% for NT3-SE®, 25% for Thermal Ti-D®, and 109% for thermal Ti-Lite®, while on comparing the forces between 12°C to 37°C, the forces increased between 15% and 95% for NT3-SE®, 20% and 88% for thermal Ti-D®, and 26% and 78% for thermal Ti-Lite®. The value of residual strain was greater at low temperatures and smaller at higher temperatures, while no significant differences were detected between 37°C and 50°C. Conclusions The temperature degree deeply affected the mechanical behavior of all test NiTi wires; the superelastic type behaved similarly to thermal wires. Increasing the temperature degree leads to more unloading forces and less residual strain.

Effect of lignin on veneer densification and set-recovery

Wood densification, aimed at enhancing mechanical properties through compression, faces challenges due to set-recovery, where densified wood regains its original shape upon re-moistening. However, understanding the role of lignin in set-recovery remains elusive. In this study, acidified sodium chlorite was applied to achieve approximately 50 % delignification without removing other wood components from 3.2 mm veneers of birch, aspen, and grey alder. The veneers were then densified at 100°C and 6 MPa, with wood moisture contents (MC) of 10 % and 16 %. The morphology, physical properties, and dimensional stability of densified wood are studied in relation to delignification and MC at densification. Delignification with subsequent densification at 16 % MC was better than at 10 % MC, increasing the resultant wood density by 89 %, 148 %, and 146 % for birch, aspen, and grey alder, respectively. In general, delignification and higher moisture content during compression resulted in better compression ratios and lower set recovery. This delignification-densification approach reduced set-recovery across all wood species to a range of 71–86 %, suggesting that under these conditions, lignin has only a marginal impact on shape memory and unrestrained set-recovery in wood. Therefore, cellulose microfibrils are likely playing a dominant role.

Smart and Sustainable 3D-Printed Nanocellulose-Based Sensors for Food Freshness Monitoring.

Annually, about one-third of the food produced around the world is wasted due to spoilage. Food contamination and spoilage, along with the use and disposal of nondegradable packaging materials, impact human health and have huge economic and sustainability implications. Achieving sustainability within the food system requires innovative solutions to reduce the environmental footprint. Herein, we describe the formulation, scalable manufacturing, and characterization of three-dimensional (3D)-printed sensors prepared from a mixture of edible biopolymer hydrogels, 8% alginate, and 10% gelatin and nanocellulose (CNC) as a reinforcement filler. We demonstrate that incorporating CNC improves the overall mechanical performance of the printed film and enables the stabilization of pH-responsive dyes for monitoring the release of total volatile basic nitrogen (TVB-N), an indicator of food freshness. Mechanical performance enhancement includes increases of 43% in load-depth indentation, 28.2% in hardness, and 17.4% in elastic modulus. This enhancement facilitates its use as a smart label technology, enabling the visual assessment of spoilage when placed inside packaging over a period of 3 days at room temperature. The 3D-printed film exhibits excellent durability, flexibility, shape memory, and robustness, along with pH responsiveness, showing distinctive color changes over the pH range of 2 to 13. These performances are demonstrated in packaged meat and fish, enabling monitoring over several days and illustrating potential as a real-time freshness indicator. The material formulations developed in this work are biodegradable, eco-friendly, and inexpensive, making them suitable candidates for smart and sustainable food packaging.