Smart Materials and Structures

High energy dissipation materials are crucial for impact protection gear. Additionally, if these materials also have shape memory property, they can offer a better body fit and increase comfort feeling. Herein, we present a novel auxetic composite foam with ultrahigh specific energy dissipation (SED) and shape memory property, which was prepared by directly foaming with low-melting-point alloy (LMPA) in polyurethane (PU) followed by thermal compression process. Due to the synergetic action of LMPA and auxetic PU foam (APU), APU/LMPA foam showed better energy dissipation than pristine PU foam. The compression test showed the energy dissipation and SED of the APU/LMPA foam were 13.4 times and 4.8 times higher than non-APU foam, respectively. Furthermore, the SED improvement of APU/LMPA foam was much higher than other reported auxetic foams. The impact test demonstrated that APU/LMPA foam with 30% thinner thickness could reduce transmitted peak force by 62.1% compared to non-APU foam. Additionally, APU/LMPA foam exhibited shape memory effect due to the phase transition of LMPA, allowing it to adapt to different body shapes through thermal process. With its outstanding energy dissipation and shape memory properties, this composite foam is highly promising for personal safety protection, offering excellent user experience.

Shape memory alloys (SMAs) are unique materials capable of recovering predefined shapes through reversible phase transformations between austenite and martensite phases. This behavior enables SMAs to exhibit the shape memory effect and pseudoelasticity, allowing for the recovery of large strains and the generation of significant forces. These properties make SMAs highly desirable for applications in actuation, sensing, and other engineering domains. Conventional SMA actuator designs, while effective, often face limitations such as slow response times, non-uniform stress distribution, and reduced fatigue life under cyclic loading. Integrating Kirigami-inspired techniques into SMA actuator design addresses these challenges by introducing precise cut patterns that transform 2D SMA materials into complex 3D structures. Kirigami-based SMA structures offer enhanced stroke lengths, improved heat dissipation, and uniform load distribution, reducing stress concentrations and extending the actuator lifespan. This approach enables the creation of versatile and efficient actuators with tailored mechanical properties, overcoming traditional design constraints. This paper presents a constitutive model for Kirigami-based SMA structures, coupling mechanical deformation and thermal response modeling to capture in-plane and out-of-plane deformations. The proposed framework provides a detailed understanding of the unique thermomechanical behavior of Kirigami-inspired SMA actuators, offering insights into their performance under varying operational conditions. The findings highlight the potential of Kirigami-based SMA structures for advancing actuator technologies across a range of applications.

A bistable composite cylindrical structure is a thin-walled shell, stable in its extended and coiled configurations, that offers large shape-morphing capabilities without structural damage. It has been successfully applied to deployable structures and launched into orbit. Smart-morphing designs provide new freedom and flexibility for space-deployable mechanics, reducing structural weight and complexity. Here, we present a novel magnetically activated bistable composite cylindrical structure, where the fundamentals of the critical magnetic driving boundaries are revealed for the first time to develop a reversed smart-morphing design principle. This is achieved by employing a magnetically responsive area within a bistable composite, where the NdFeB particles are co-cured directly with the carbon layups to ensure good bonding. Theoretical analysis of the magnetic driving principle was developed to reveal the interacting mechanics of a bistable structure subjected to magnetic actuation. The magnetic field distribution was characterized through experiments; a series of magnetic-responsive bistable composite cylindrical samples were produced and subjected to magnetic activation to determine the critical shape transition intensities. Their shape-changing processes were also evaluated through mechanical testing and compared to the magnetic driving mechanics. It is found that there is an optimal level of magnetic particle concentration to minimize the magnetically responsive time and input energy. The critical boundaries in terms of the current and air gap are established through theoretical analysis and verified through experimental observations. The magnetic driving mechanics are then discussed and concluded in detail. This provides a simple and effective alternative for smart actuation and morphing control of bistable composite structures, supporting their future applications in deep space exploration.

The concept of smart structure reflects the current Industry 4.0 principles, where manufacturing facilities function as smart systems, capable of self-awareness through sensing capabilities and real-time adaptability to market demands leading to the idea of cyber-physical systems (CPS). These concepts are particularly relevant for the space industry, which is experiencing rapid changes due to the entrance of private companies and the emergence of satellite mega-constellations. In this paper the authors propose a framework for leveraging Industry 4.0 concepts in manufacturing processes of the space industry, emphasizing the role of CPS and identifying smart structures as archetypes.

Stick-slip piezoelectric motors (SSPEMs) are widely regarded as promising candidates for precision positioning systems due to their compact structures and simple driving modes. However, challenges inherent to conventional SSPEMs, including backward motion and instability, seriously limit the output speed of SSPEMs at high driving frequencies. Inspired by the driving principle of impact inertial PEMs, this paper proposes an impact-enhanced driving mode that enables SSPEMs with smoother ripple motion and improved driving frequencies compared to conventional driving modes. The proposed driving mode utilizes the parasitic motion of the compliant mechanism (CM) and the inertia of the driving foot to generate larger force to the mover at high driving frequencies, so that the backward motion can be eliminated and the output performance can be improved at high frequency. To validate the proposed driving mode, an SSPEM with modified triangular configured CM is carefully designed by analytical models and finite element simulation. A prototype is then fabricated for validation. Experimental results show that the backward motion is eliminated when the driving frequency exceeds 800 Hz. Comparative results further highlight the advantages of the impact-enhanced driving mode, achieving a maximum driving frequency of 1800 Hz and a peak velocity of 38.19 mm s⁻¹. The proposed impact-enhanced driving mode offers a universal and effective solution for SSPEMs with parasitic-motion CMs, significantly improving speed, accuracy, and high-frequency one-step stability.

Research into sustainable energy sources has gained significant attention due to global environmental challenges. Vibration energy harvesting (VEH) presents a promising approach for developing self-powered sensors, offering both practical and environmental benefits. This paper reviews recent advancements in VEH with a specific focus on piezoelectric-based methods. It classifies the key techniques in the literature into categories such as multistability (including bistability), internal resonance, optimized designs, and frequency-up conversion. The paper discusses the underlying principles of each technique, provides relevant illustrations, highlights recent studies within each category, and summarizes their main contributions.

Advancements in intelligent materials for the past few decades enabled the development of functional morphing structures and robots operating in fluid environments. Fluid-structure interaction (FSI) problems for functional morphing structures and robots were naturally accentuated. In this paper, the recent advancements in shape-morphing robots and structures in fluid flow across different Reynolds number scales are reviewed and summarized, from microrobots with Reynolds numbers much lower than 1 to deformable aircraft in turbulent flows. To improve the design and functionality of the morphing structures and robots, we discuss modeling methods, experiments, and materials for the morphing structures over a vast range of Reynolds numbers. Understanding FSI in designing morphing structures and robots is emphasized. Following up with several critical future questions to address, the potential applications of artificial intelligence and machine learning (AI/ML) techniques in improving the design of shape-morphing structures and robots are discussed. These shape-morphing structures are expected to significantly enhance sustainable solutions for challenges and explore the unknown of deeper oceans and outer space.

Active (intelligent/smart) materials in engineering solutions are generally combined with other materials, and they are embedded in physical environments. In the current work, these kinds of systems are described as soft–hard active–passive embedded structures (SHAPES). The term emphasizes the interacting materials: In the same way as soft–hard is a spectrum of mechanical compliance, active–passive describes a spectrum of multi-field compliance, i.e. the strength of reaction to a non-mechanical stimulus like a temperature change or an applied electric field. SHAPES can be classified according to the interaction of the active and passive materials as having a Case I (the expansion of the active material is mostly constrained by the passive material), Case II (a combined deformation behavior ensues which is influenced by the active and passive materials) or Case III (the active material deforms freely with only negligible influence of the passive material) behavior. Various application concepts for SHAPES as actuators or for other applications—such as morphing, conductivity switching, sensing, connection-breaking, blocking, and material logic—are presented. Furthermore, the most common active materials that can be part of SHAPES are discussed with respect to their stimulus-responsivity. From these, design recommendations for SHAPES-like applications are derived. Two tables that give a comprehensive overview of relevant literature sources are provided. These tables serve as a snapshot of the currently applied materials and the realized concepts. They can serve as a starting point to add new and emerging materials. The unique focus of the present review is the classification of the interacting materials and how authors utilize the properties of the active and passive materials inside their composites. This allows the identification of gaps/shortcomings in the field and opportunities for new SHAPES designs.

Soft body armor composites are broadly utilized for individual security due to their light weight and flexible nature. However, they are not viable in halting high-velocity impact, particularly against impact at a near distance. Integrating shear thickening fluids (STFs) into these composites is a promising result of upgrading their impact resistance. This review article highlights the progress in improving the impact resistance of soft body armor composites due to the incorporation of STFs. It discusses the parameters affecting energy absorption, shear thickening fluid properties, rheological properties of STFs, mechanisms of energy dissipation during the impact, fabrication techniques of STF-fabric composites, ballistic test techniques, and challenges of ballistic performance evaluation and wearer consolation. This review paper incorporates previous research work for experimental and numerical simulation results. In general, the integration of STFs into soft body armor composites showed noteworthy guarantees in the impact resistance capabilities of soft body armor composites. The most frequent applications of soft body armor composites are security personnel, civilian applications, emergency response teams, private security, body guards, law enforcement, and the military.

Ultrasonic guided waves (UGWs) can travel long distances within the detected structures, which is of great significance for monitoring large complex engineering systems. However, the multimodal and dispersive properties of the specific research object making this promising whole structure monitoring difficult to interpret the signal mathematically and physically. With the development and maturity of deep learning and big data mining technologies, many scholars have noticed artificial intelligence algorithms such as deep learning can provide a new tool in UGWs signal processing, avoiding the mechanism analysis difficulties in the application of UGWs. But the integrity of structural state data sets has become a new pain point in engineering applications under this new approach, and how to apply the knowledge obtained from the existing data set to different but related fields through knowledge transfer in such cases begin to attract the attention of scholars and engineers. Although several systematic and valuable review articles on data-driven UGWs monitoring methods have been published, they only summarized relevant studies from the perspective of data-driven algorithms, ignoring the knowledge transfer process in practical application scenarios, and the intelligent UGWs monitoring methods based on knowledge transfer of incomplete sets are still lacking a comprehensive review. This paper focuses on the UGWs transfer monitoring technology when the training sample is missing, explores the feature correlation between samples in different domains, improves the transfer ability of the structural monitoring model under different conditions, and analyzes the UGWs intelligent monitoring methods for structural state under different sample missing conditions from three aspects: semi-supervised monitoring, multi-task transfer and cross-structure transfer. It is also expected to provide a new method and approach to solve the condition monitoring problems in other complex scenarios.

Tensegrity metamaterials are considered superior to traditional materials in engineering due to their exceptional variable stiffness, adaptive load–bearing capabilities, and adjustable morphing properties. This paper presents a novel negative Poisson's ratio tensegrity metamaterial featuring a substructure composed of a D–bar tensegrity structure and a rotating double–square negative Poisson's ratio structure. Firstly, we establish the geometric model of the D–bar tensegrity structure and determine the pretension relationships among its tension elements. We then describe the composition of the tensegrity metamaterials and their performance metrics. The stress–strain behavior of tension elements is characterized through tensile tests. Further experiments explore the effects of structural angle and pretension on the compressive load–displacement characteristics of the structure. Then, the effect of the structural angle of tensegrity metamaterial substructures on energy absorption is analyzed. Additionally, the impact resistance of tensegrity metamaterials with negative Poisson's ratios shows significant compressive and impact durability. Their potential for enhancing drone protection and environmental adaptability is also demonstrated.

In response to growing innovation demands in aviation, open-fan propulsion systems have gained renewed attention owing to their high propulsion efficiency. However, these systems introduce substantial low-frequency acoustic excitation on the aircraft fuselage, dominated by the fundamental blade pass frequency, which poses challenges for managing cabin noise and structural vibrations. This study investigates the integration of vibroacoustic metamaterials and ferroelectrets as a synergistic approach for vibration mitigation and energy harvesting in aircraft fuselages. The proposed vibroacoustic metamaterial demonstrates a vibration attenuation of up to −21.6 dB at the fundamental blade pass frequency of 300 Hz, accompanied by a maximum reduction of −18.3 dB in radiated sound power into the cabin. Electromechanical performance evaluation indicates that this approach enables broadband energy harvesting with a power conversion efficiency of up to 2.85 %, providing sufficient energy to sustain low-power sensor systems. This combination of novel technologies offers a promising pathway for enhanced noise control and self-powered sensing in next-generation aircraft and thin-walled structures in lightweight design.

McKibben artificial muscle is a fluid-driven soft actuator comprising sleeve fibres and a rubber tube, which contracts by fluid pressure. A part of the side of the artificial muscle is reinforced with a reinforcement material to suppress contraction in that area, thereby achieving the bending motion. In this study, we propose a novel fabrication process to realise bending-type smart artificial muscles (B-SAMs) that sense their curvature by using optical fibres as the reinforcement material. The optical fibre also serves as a curvature sensor owing to the attachment of a light emitter and light receiver on each end of the fibre. A braiding machine is employed to fabricate B-SAM, allowing the optical fibre to be integrated with the sleeve fibres to cover the rubber tube, rendering mass production easy. The versatility of the proposed method is demonstrated through fabricating and evaluating a soft mechanism with two bending units using this fabrication technique. The proposed simple and efficient fabricating process can promote the practical application of artificial muscles.

The Ni49+xMn32-2xGa19+x (x = 0; 2) Heusler ferromagnetic shape memory alloys were prepared using spark plasma sintering using raw flake-type powders obtained by soft grinding melt-spun ribbons. Samples were characterized using X-ray diffraction, electron microscopy, thermal analysis, and bending tests. Although the properties of ribbons and corresponding powders show similar properties' tendencies, they are opposite in the bulk sintered alloys when compared with precursor powders. Namely, Ni49Mn32Ga19 bulk shows a higher enthalpy (5.8 J/g), an increased martensitic transformation temperature (by 9 K), and a reduced hysteresis span (5 K). Conversely, for the Ni51Mn28Ga21 sintered sample, a lower enthalpy (2 J/g), a significant decrease (by 40 K) in the martensitic transformation starting temperature, and a broadening of the hysteresis range (26 K) were observed. This difference is analyzed versus specific features of the microstructure. Moreover, the activation energy and the pre-exponential factor of the martensitic transformation, extracted through kinetic analysis within two non-isothermal models, Kissinger and Friedman, complement and sustain these findings. Fractography details of the sintered samples are discussed in relation to the stress-strain curves from the bending tests. The Ni49Mn32Ga19 bulk sample exhibits a higher bending strength (260 MPa) and a lower strain (0.55 %) than the Ni51Mn28Ga21 sample (177 MPa and 0.61 %). The observed dependence of functional characteristics on preparation enables the possibility of property control required for various applications and suggests that the proposed route is promising in this regard for further investigations.

This paper introduces a novel fused deposition modeling 3D printing technique for
producing high-strength, lightweight components, referred to as jigsaw printing. The
proposed method can effectively integrate the filling patterns and filling densities of
multiple 3D-printed internal structures into a single component. The filling density of
the printed part can be continuously varied along a certain direction, thereby achieving
a functional gradient. Notably, this method is simple, effective, and compatible with
standard 3D printers without the need for specialized slicing software.
By utilizing this approach, we design and print a novel quasi-isostrength beam
using a single resin material. The density of the fabricated beam changes continuously
along its length through a combination of regions of high and low filling densities.
Unlike conventional equal-strength beams, the proposed beam demonstrates a uniform
external appearance and achieves almost the same strength across multiple surfaces
compared with the 100% uniform beam. The proposed method reduces material
consumption and printing time while retaining approximately 94–95% of the strength of
a 100% uniform beam with similar dimensions. Moreover, the weight of the fabricated
beam is only 67% that of the 100% uniform beam. Testing indicates that the specific
strength of the proposed beam is 1.42 times that of a 100% uniform beam.

In response to growing innovation demands in aviation, open-fan propulsion systems have gained renewed attention owing to their high propulsion efficiency. However, these systems introduce substantial low-frequency acoustic excitation on the aircraft fuselage, dominated by the fundamental blade pass frequency, which poses challenges for managing cabin noise and structural vibrations. This study investigates the integration of vibroacoustic metamaterials and ferroelectrets as a synergistic approach for vibration mitigation and energy harvesting in aircraft fuselages. The proposed vibroacoustic metamaterial demonstrates a vibration attenuation of up to −21.6 dB at the fundamental blade pass frequency of 300 Hz, accompanied by a maximum reduction of −18.3 dB in radiated sound power into the cabin. Electromechanical performance evaluation indicates that this approach enables broadband energy harvesting with a power conversion efficiency of up to 2.85 %, providing sufficient energy to sustain low-power sensor systems. This combination of novel technologies offers a promising pathway for enhanced noise control and self-powered sensing in next-generation aircraft and thin-walled structures in lightweight design.

The Ni49+xMn32-2xGa19+x (x = 0; 2) Heusler ferromagnetic shape memory alloys were prepared using spark plasma sintering using raw flake-type powders obtained by soft grinding melt-spun ribbons. Samples were characterized using X-ray diffraction, electron microscopy, thermal analysis, and bending tests. Although the properties of ribbons and corresponding powders show similar properties' tendencies, they are opposite in the bulk sintered alloys when compared with precursor powders. Namely, Ni49Mn32Ga19 bulk shows a higher enthalpy (5.8 J/g), an increased martensitic transformation temperature (by 9 K), and a reduced hysteresis span (5 K). Conversely, for the Ni51Mn28Ga21 sintered sample, a lower enthalpy (2 J/g), a significant decrease (by 40 K) in the martensitic transformation starting temperature, and a broadening of the hysteresis range (26 K) were observed. This difference is analyzed versus specific features of the microstructure. Moreover, the activation energy and the pre-exponential factor of the martensitic transformation, extracted through kinetic analysis within two non-isothermal models, Kissinger and Friedman, complement and sustain these findings. Fractography details of the sintered samples are discussed in relation to the stress-strain curves from the bending tests. The Ni49Mn32Ga19 bulk sample exhibits a higher bending strength (260 MPa) and a lower strain (0.55 %) than the Ni51Mn28Ga21 sample (177 MPa and 0.61 %). The observed dependence of functional characteristics on preparation enables the possibility of property control required for various applications and suggests that the proposed route is promising in this regard for further investigations.

High energy dissipation materials are crucial for impact protection gear. Additionally, if these materials also have shape memory property, they can offer a better body fit and increase comfort feeling. Herein, we present a novel auxetic composite foam with ultrahigh specific energy dissipation (SED) and shape memory property, which was prepared by directly foaming with low-melting-point alloy (LMPA) in polyurethane (PU) followed by thermal compression process. Due to the synergetic action of LMPA and auxetic PU foam (APU), APU/LMPA foam showed better energy dissipation than pristine PU foam. The compression test showed the energy dissipation and SED of the APU/LMPA foam were 13.4 times and 4.8 times higher than non-APU foam, respectively. Furthermore, the SED improvement of APU/LMPA foam was much higher than other reported auxetic foams. The impact test demonstrated that APU/LMPA foam with 30% thinner thickness could reduce transmitted peak force by 62.1% compared to non-APU foam. Additionally, APU/LMPA foam exhibited shape memory effect due to the phase transition of LMPA, allowing it to adapt to different body shapes through thermal process. With its outstanding energy dissipation and shape memory properties, this composite foam is highly promising for personal safety protection, offering excellent user experience.

Shape memory alloys (SMAs) are unique materials capable of recovering predefined shapes through reversible phase transformations between austenite and martensite phases. This behavior enables SMAs to exhibit the shape memory effect and pseudoelasticity, allowing for the recovery of large strains and the generation of significant forces. These properties make SMAs highly desirable for applications in actuation, sensing, and other engineering domains. Conventional SMA actuator designs, while effective, often face limitations such as slow response times, non-uniform stress distribution, and reduced fatigue life under cyclic loading. Integrating Kirigami-inspired techniques into SMA actuator design addresses these challenges by introducing precise cut patterns that transform 2D SMA materials into complex 3D structures. Kirigami-based SMA structures offer enhanced stroke lengths, improved heat dissipation, and uniform load distribution, reducing stress concentrations and extending the actuator lifespan. This approach enables the creation of versatile and efficient actuators with tailored mechanical properties, overcoming traditional design constraints. This paper presents a constitutive model for Kirigami-based SMA structures, coupling mechanical deformation and thermal response modeling to capture in-plane and out-of-plane deformations. The proposed framework provides a detailed understanding of the unique thermomechanical behavior of Kirigami-inspired SMA actuators, offering insights into their performance under varying operational conditions. The findings highlight the potential of Kirigami-based SMA structures for advancing actuator technologies across a range of applications.

In-plane thin dielectric elastomer actuators (DEAs) represent a promising solution for miniaturised soft robots capable of navigating confined spaces. However, most existing in-plane DEAs are either fabricated using off-the-shelf materials or rely on membranes attached to rigid frames, which limit their actuation performance and pose challenges for integration into locomotion-based soft robots. This work introduces a novel in-plane DEA-based thin soft-rigid hybrid robot for fast movement. The innovative design features a multi-layer silicone-based elastomer tensioned by an in-plane elastic PETG frame. A detailed spin coating fabrication method is presented for producing multilayer silicone-based in-plane DEAs. The robot demonstrated effective crawling on flat surfaces and resonance-driven high-speed locomotion at 53 Hz, achieving a peak velocity of approximately 12.3 mm/s which is 34.2% of its body length per second and 224% of body thickness per second. This study highlights the potential of DEAs for advancing miniaturised soft robotics, especially in applications that demand lightweight, flexible, and thin profile actuators.

Magnetic shape memory polymers (MSMPs) represent a new family of smart materials that unify the tunable mechanical properties typical for shape memory polymers (SMPs) with remote actuation abilities utilizing magnetic fields. First developed in the late 20th century, these MSMPs leverage recent developments in polymer technology and material science for enhanced functionality, placing these materials as key components in several applications, from biomedical devices to soft robotics and smart textiles. This focused review aims to comprehensively summarize the fundamental mechanisms, constituents, and principal applications of MSMPs. Furthermore, non-contact shape recovery methods such as magnetic induction heating or magneto-mechanical forces are also realized by integrating the particles (e.g., iron oxide, cobalt ferrite) with the polymer matrix. The authors of this paper review methods to fabricate uniform particle dispersion and how the selection of polymer can lead to changes in thermal and mechanical properties due to the incorporation of particles into them; they also comment on maintaining a balance between efficiency, durability, and scalability against optimizing. Emphasis is placed on the review of multiple applications of MSMPs in areas like biomedicine, soft robotics, and self-healing materials that require precise manipulation. This review provides a detailed summary of the current constraints, such as particle aggregation, long-term stability, and production costs, while also suggesting key areas that could improve the effectiveness and utility of MSMPs. This analysis aims to describe the current landscape in MSMP research, its technological potential, and areas that require further development.

In the pursuit of solving the energy storage issues of leadless pacemakers, this study presents a piezoelectric energy harvester for self-powering. The mismatch in natural frequencies between the cardiac cycles and the piezoelectric structure affects energy generation. In this research, a groundbreaking hexa-fold piezoelectric energy harvester (HF-PEH) with contact impacts was proposed to generate high energy density from cardiac cycles. The HF-PEH was manufactured and tested in vivo inside a living pig's heart. Subsequently, we subjected this HF-PEH prototype to laboratory cardiac acceleration for over 35 million cardiac cycles to investigate its long-term performance. Post-test material analysis using SEM and X-ray energy-dispersive spectroscopy (EDS) was conducted to investigate the material structure. The HF-PEH generated maximum voltage, current, and power of 1.4 V, 458.5 µA, and 367.2 µW at in-vivo animal trial with 71 beats per minute, which are the same or higher than the values a leadless pacemaker paces into the body. Post-test material analyses showed that the piezoelectric ceramic remained intact while the electrode condition changed. A verified finite element model was used to study the long-term electrode layer erosion condition with respect to the electric displacement field. Since the electrode erosion is limited to the contact-based impact region, limited power degradation in long-term performance was observed. This study also highlights the roles of electrode materials and presents potential protective methods and materials to mitigate electrode performance degradation. Our findings pave the way for practical energy harvesting applications for leadless pacemakers and underscore the need for advanced piezoelectric coatings in contact-based energy harvesting systems.

Dielectric Elastomer Actuators (DEAs) are a recent type of smart materials that show impressive performances as soft actuators, making them a promising technology for the development of implantable artificial muscles and soft robotic devices. Notably, they are explored as implants for the restoration of facial movements post paralysis. However, implementing DEAs that mimic natural muscles has been proven difficult, as DEAs provide in-plane expansion when actuated, while natural muscles contract upon stimulation. Multiple solutions can be found in literature, namely stack DEAs and fiber-reinforced DEAs. The fibers used for DEAs to achieve contractile motion rely on a fishnet design, where the angle between the fibers, the spacing, mechanical properties as well as the fiber dimensions can be set by establishing a fiber analytical model. Contraction has only been achieved with
DEAs based on acrylic elastomer and pre-stretched with rigid frames, thus making them unsuitable as soft implants. This work introduces the first silicone-based, non-pre-stretched DEAs presenting in-plane contractile behavior by embedding such soft structured fiber sheets in the actuators. Fiber-reinforced DEAs were shown to achieve modest contractile strains, particularly with optimal fiber angles between 55° and 65°, enhancing their ability to mimic muscle-like behavior. A peak occurs at approximately 60°, where the maximum contraction of -0.6% was achieved, resulting in a 3 % error from the model. The low contractile strains of silicone-based DEAs indicate that further optimization is needed for real-world applications

The superelasticity of shape memory alloys (SMA) can be used to provide self-centering and/or energy dissipation characteristics to structures including buildings, bridges, automobiles, and aircrafts. The functional fatigue behavior of SMA is important because it affects the stiffness, strength, strain recovery and energy dissipation of the material. This study investigated the functional fatigue behavior of large diameter Ni–Ti SMA bars under different levels of plastic deformation and different ambient temperatures. Differential scanning calorimetry was used to measure the martensitic transformation temperatures. Cyclic loading with a 1% strain increment was applied to investigate the maximum recovery strain, i.e. the superelastic limit. Low-cycle fatigue loading with different applied peak strains (2%, 3%, 4% and 5%) was performed at different temperatures (−40 °C, −10 °C, 10 °C, 25 °C and 50 °C). The effects of plastic deformation, testing temperature, and number of cycles on the stress-induced martensitic phase transformation, degradation of superelastic properties, and fatigue life were studied. The superelastic properties, such as the changes in the stress–strain curves, elastic modulus, yield stress, damping ratio and recovery strain, were analyzed. It was shown that the functional fatigue resistance (in terms of degradation in the superelastic properties and fatigue life) of Ni–Ti SMA reduced as the applied peak strain increased, particularly when the applied peak strain was higher than the superelastic limit. Additionally, when Ni–Ti SMA was subjected to combined plastic deformation and higher than room temperature, the functional fatigue resistance reduced as the temperature increased.

The current work develops a physics-based model for twisted and coiled artificial muscles (TCAMs) using the extended Cosserat theory of rods. These artificial muscles are lightweight and low-cost, generating a high power-to-weight ratio. They produce tensile forces up to 12 600 times their own weight, closely mimicking the functionality of biological muscles. The contraction of these muscles is driven by the anisotropic volume expansion of their twisted fibers, induced by deformation of the fibers' cross-section. Unlike prior models, this study implements the extended Cosserat theory, which models not only rigid rotations (like standard Cosserat theory) but also planar anisotropic deformation of the TCAMs' cross-section. The static deformation and dynamic motion of TCAMs are formulated herein. The governing equations for the bulk deformation of TCAMs are derived through standard Cosserat rod theory, while a continuum mechanics approach is utilized to model the cross-sectional deformation. The Bernstein polynomial method is applied to discretize the continuous formulations, enabling numerical solutions to the problem. Experimental datasets are used for evaluation of the models.