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As an important part of many mechanical equipment, the mechanical transmission system is very important to carry out efficient and accurate fault monitoring and diagnosis. Compared with traditional fault diagnosis techniques, such as spectrum analysis, deep learning has been widely used in the field of mechanical system fault diagnosis due to its powerful data expression ability, and has achieved certain research results. One-dimensional convolutional neural network is a widely used model for deep learning, so in this paper, the one-dimensional convolutional neural network (1D-CNN) in the deep learning theory and the vibration signal analysis method are integrated and applied to the fault identification of mechanical transmission system to achieve accurate diagnosis and classification of faults. The experiment is mainly to collect the vibration signal data of different fault states such as broken teeth, cracking, shaft unbalance, bearing wear, and excessive friction of the driven wheel of the mechanical transmission system, it was divided into training set and testing set according to an appropriate proportion, and 1D-CNN was built using Python. The deep learning model deeply analyzed the influence of different data sample sizes and different model parameters on the recognition accuracy, and obtained an ideal diagnostic model based on variable learning rate through parameter adjustment and comparative analysis. This experimental results show that the recognition method based on one-dimensional convolutional neural network can be effectively applied to the fault diagnosis of related mechanical transmission, and has a high diagnosis accuracy.

Electroadhesion has shown the potential to deliver versatile handling devices because of its simplicity of actuation and rapid response. Current electroadhesion systems have, however, significant difficulties in adapting to external objects with complex shapes. Here, a novel concept of metasurface is proposed by combining the use of natural fibers (flax) and shape memory epoxy polymers in a hygromorphic and thermally actuated composite (HyTemC). The biobased material composite can be used to manipulate adhesive surfaces with high precision and controlled environmental actuation. The HyTemC concept is preprogrammed to store controllable moisture and autonomous desorption when exposed to the operational environment, and can reach predesigned bending curvatures up to 31.9 m

Shape memory polymers (SMPs) have received immense attention from materials research community thanks to their unrivaled properties such as high recoverable strains (up to 400%), low weight, tailorable properties, easy processing, and multiple activation methods. Researchers in both academia and industry have been proposing, experimenting, analyzing, and reporting on various aspects of these materials from synthesis to their applications. Such efforts have led to skyrocketing research output in terms of published papers, especially in the last half a decade. Despite the flourishing research, numerous challenges that hinder advanced applications still exist with the predominant one being the low mechanical properties. To circumvent these challenges, various types of reinforcements have been utilized, leading to significant enhancements and widened potential applications. This work presents an overview of the present research on active composites. Areas covered include the background of SMPs, reinforcements, fabrication techniques, stimulus methods, and applications. Our review is particularly unique in that we included discussions on the various fabrication techniques for SMP composites including their merits and demerits which, to the best of our knowledge, is the first review to include such discussion, thus making it a complete reference material.

The compatibility of polylactic acid (PLA)/polybutylene succinate (PBS) blends was studied by molecular dynamics and mesoscopic dynamics, which is a controversial issue in experiments. Six simulation models of PLA/PBS with different composition ratios (100/0, 90/10, 80/20, 70/30, 60/40, 0/100) were constructed. The radial distribution function, hydrogen bond, free energy density, order parameter and iso-density surface morphology of the PLA/PBS systems were simulated and analyzed. Due to the formation of hydrogen bonds and van der Waals bonds between different elements of PLA chains and PBS chains, the PLA/PBS blends exhibit good compatibility at all composition ratios.

Due to the inherent rigidity of hard materials, the adaptability and flexibility of traditional robots are limited. Recently, soft robots became one of the most attractive areas. The intrinsic compliance and adaptability of soft materials enable soft robots to achieve unexpected functions. Dielectric elastomers (DE) can exhibit large deformation, fast response, and high energy density under the action of external electrical stimuli, becoming one of the most promising materials in soft robots. Herein, the key points of DE actuators (DEAs) are first introduced, including the working principle, DE materials, compliant electrodes, and typical configurations. Then, the soft robots driven by DEAs are reviewed. Some recent highlights are described and discussed in detail. Finally, the main challenges are summarized for the real‐world application of soft robots based on DEAs.

Development of the power industry, especially in the field of high-power electricity, is limited by the insulating materials. The main problem of power generation equipment, especially ultra-high-voltage and high-power equipment, is the ability of insulating materials to withstanding voltage. Epoxy resin (EP) is widely used in the power industry. Therefore, it is necessary to improve the performance of EP and demonstrate an energy model of material electrical breakdown. EP has excellent insulation properties, yet poor toughness. By doping with nanomaterials, the toughness of the matrix can be improved on the premise of having little influence on insulation performance. In this paper, two kinds of nanomaterials were added into the matrix, namely multi-walled carbon nanotubes (MWCNTs) and organically modified montmorillonite (OMMT). MWCNTs are conductive, and the insulation properties of EP will be adversely affected if doped in large quantities. OMMT is a nanomaterial with lamellar structure. The toughness of EP can be improved by being doped with OMMT without adverse effect on the insulation performance. Various factors affecting the electric field strength and dielectric properties are analyzed, and models of electric and thermal breakdown are established. In addition, by observing the phenomena of material after breakdown, the energy relation equation of breakdown is re-established.

Shape-memory polymers (SMPs) and their composite materials are stimuli-responsive materials that have the unique characteristics of lightweight, large deformation, variable stiffness, and biocompatibility. This paper reviews the research status of the mechanical models for SMPs, shape-memory nanocomposites and shape-memory polymer composites (SMPCs); it also introduces some spatially deployable structures, such as hinges, beams, and antennae based on SMPCs. In addition, the deformation types of 4D printing structures and the potential applications of this technology in robots and medical devices are also summarized.

The thermo-mechanical properties of unidirectional carbon fiber reinforced epoxy-based shape memory polymer (SMP) composites with fiber mass fractions of 16%, 23%, 30%, 37% are evaluated by using three-point bending tests. The SMP composites show temperature-dependent flexural modulus and strength, with one order of magnitude difference between 120 °C and 20 °C. The composites show good shape recovery capability, with measured recovery ratios of more than 93% at 120 °C and 100% after 20 min at that temperature. The recovery stresses increase nonlinearly during reheating; the maximum recovery stress is approximately proportional to the fiber mass fraction. The composites show recovery capability under external loads, with the recovery ratio being inversely proportional to the partial load level. The composites feature good shape memory properties during cyclic loading and unloading at 120 °C. Their loss factors and stiffness losses decrease significantly during the first three cycles, and then stabilize after ten cycles.

Self-deployable structures based on shape memory polymer composites (SMPCs) have the capability of self-deploy, light weight and high load-bearing. This paper presents the detail of an integrative hinge fabricated by carbon fiber reinforced shape memory epoxy composites in the sequence of material selection, structure design and manufacture, material and structure experiments, and application. DMA experiments have been conducted to figure out the temperature sensitivity of SMP. The temperature dependent elastic modulus and strength of SMPC were determined by tensile experiments. Results from three point bending tests and shape memory recovery tests verify the variable stiffness of the integrate SMPC hinge under different temperatures and superior shape memory properties. Strain distribution during bending process are obtained from both digital image correlation (DIC) measurements and ABAQUS simulation, showing good consistency with each other. To compare the modal characteristics with traditional SMPC hinge, modal testing and computation have been designed with free boundary condition. It can be found that the integrative SMPC hinges have the characteristics of improved reliability and performance, and higher post-deployment stiffness and strength, when compared to traditional SMPC hinges. Finally, prospective applications of the self-deployable structure have also been illustrated.

4D printing adds time as the fourth dimension to 3D printing, which has been actively explored in the biomedical field to develop patient-specific implants due to the ease of manufacturing complex architectures and the capability of dynamic transformations. However, the 4D printing filament used for fused deposition modeling (FDM) is quite limited. Here, 4D printing shape memory polybutylene succinate/polylactic acid (PBS/PLA) composite filament is prepared. The mechanical properties, surface morphology, and shape memory performances of the printed specimens are investigated. Besides, graphene oxide functionalized PBS/PLA shows attractive photothermal properties under near-infrared (NIR) irradiation, and a dynamic, remote, and accurate controlled 4D transformation of a porous scaffold is exhibited. As the first demonstration of 4D printing filament of PBS/PLA for FDM, this work shows its promising application prospects in tissue engineering, photothermal therapy, etc. Additionally, NIR-triggered 4D transformation solves the problem that the conventional thermal-trigger transformation process is difficult to control.

In recent years, shape memory polymer composites (SMPCs) have been gradually applied to space deployable structures owing to their shape memory characteristics and superior mechanical properties. This study investigated structural and dynamic analysis of an SMPC flexible solar array system (SMPC-FSAS). The SMPC-FSAS was designed to ensure the safety and reliability of the structure. In addition, the modal and swept sine vibration responses of the structure were studied by numerical simulations and experiments. The experimental results were consistent with the numerical simulation predictions, which verified the correctness of the numerical model. Subsequently, a series of dynamic tests verified that SMPC-FSAS has a favorable structural strength and rigidity. Notably, the SMPC-FSAS carried on the SJ-20 geostationary satellite was successfully launched into a geosynchronous orbit, which further verified its safety and reliability. The results of this study are expected to serve the design of ultra-large flexible solar arrays in the future.

Four-dimensional (4D) printing endows three-dimensional (3D) objects with structural customizability and functional tunability, which offers the potential to manufacture advanced equipment and devices for specific structural or functional requirements. Here, we investigated the temperature-dependent mechanical and shape memory properties of 4D printed continuous fiber reinforced composite horseshoe lattice structures (CFRCHLSs). Rectangular modified CFRCHLSs with diverse cell configurations were designed and prepared by fiber/matrix co-extrusion process utilizing continuous fibers and shape memory polymer (SMP). Isothermal compression experiments and thermo-mechanical cycle experiments were conducted to investigate the temperature-dependent mechanical properties and thermally-induced active deformation capabilities of 4D printed CFRCHLSs. The results indicate that 4D printed CFRCHLSs possess temperature-dependent equivalent stiffness and peak load, and exhibit shape recovery capabilities affected by geometric configuration. Furthermore, multi-step relaxation experiments were carried out, which revealed the relaxation phenomenon of 4D printed CFRCHLSs at continuous multiple displacements. This work provides guidance for structural design, integrated preparation and characterization of thermodynamic properties of fiber reinforced composite lightweight structures with intelligent deformation behavior.

Dynamic control of liquid wetting behavior on smart surfaces has attracted considerable concern owing to their important applications in directional motion, confined wetting and selective separation. Despite much progress in this regard, there still remains challenges in dynamic liquid droplet manipulation with fast response, no loss and anti‐contamination. Herein, a strategy to achieve dynamic droplet manipulation and transportation on the electric field adaptive superhydrophobic elastomer surface is demonstrated. The superhydrophobic elastomer surface is fabricated by combining the micro/nanostructured clusters of hydrophobic TiO2 nanoparticles with the elastomer film, on which the micro/nanostructure can be dynamically and reversibly tuned by electric field due to the electric field adaptive deformation of elastomer film. Accordingly, fast and reversible transition of wetting state between Cassie state and Wenzel state and tunable adhesion on the surface via electric field induced morphology transformation can be obtained. Moreover, the motion states of the surface droplets can be controlled dynamically and precisely, such as jumping and pinning, catching and releasing, and controllable liquid transfer without loss and contamination. Thus this work would open the avenue for dynamic liquid manipulation and transportation, and gear up the broad application prospects in liquid transfer, selective separation, anti‐fog, anti‐ice, microfluidics devices, etc., Dynamic liquid droplet manipulation and transportation are demonstrated on the superhydrophobic micro/nanostructured elastomer surface via electric field, based on electric adaptive switchable wettability and tunable adhesion. This work provides a new route for precise liquid manipulation and transfer, and is promising in designing and constructing smart interface materials.

Shape-memory polymers (SMPs) can adjust their stiffness, lock a temporary shape, and recover the permanent shape upon an appropriate stimulus. They are applied in the field of morphing skins. This work presents a variable-stiffness corrugated sheet based on a carbon fiber felt (CFF)-reinforced epoxy-based SMP composite that shows variable stiffness and extreme mechanical anisotropy for potential morphing skin applications. The corrugated sheet exhibits a variable stiffness with a change in temperature, which can help the skin adjust its stiffness according to different service environments. The corrugated sheet can be electrically heated rapidly and homogeneously due to its high electrical conductivity and enhanced heat transfer efficiency. Its Joule-heating effect acts as an effective active stimulation of the variable stiffness and shape-memory effect. The CFF-reinforced epoxy-based SMP composite was manufactured into a corrugated shape to obtain extreme mechanical anisotropy. The corrugated sheet shows a low in-plane stiffness to minimize the actuation energy, while it also possesses high out-of-plane stiffness to transfer the aerodynamic pressure load. Its mechanical properties, electrical heating performance, and shape-memory effect were investigated using experiments. The results show that the proposed SMP composite exhibits extreme mechanical anisotropy, considerable deformation ability, and variable stiffness induced by Joule heating without an external heater.

Shape memory polymer (SMP) mandrel, a kind of mandrel for fabrication of composite structures, has attracted great attention due to the advantages of low cost, simple operation and easy demoulding. In this paper, a type of styrene-based SMP with good shape retainability and recoverability were synthesized and examined by uniaxial tensile test and dynamic mechanical analysis test. Then, a bottle-shaped smart mandrel with shape memory effect was prepared by inflation method. Short/long-time shape retainability and reusability were characterized. Finally, the SMP mandrel was used to form a bottle-shaped composite structure model by filament winding technology. The excellent demoulding property and good reusable ability of SMP mandrel provided potential applications in the composite part production.

We describe in this work a broadband magnetic E-shape piezoelectric energy harvester with wide frequency bandwidth. We develop first a nonlinear electromechanical model of the harvester based on the Hamilton variation principle that simulates the effect of the nonlinear magnetic restoring force at different spacing distances. The model is used to identify the distances existing between two different magnets that enable the system to perform with a specific nonlinearity. The performance of the E-shape piezoelectric energy harvester is also investigated through experiments, with E-shape energy harvesters at different spacing distances tested under several base acceleration excitations. We observe that the frequency domain output voltage of the system shows a general excellent controllable performance, with a widening of the frequency bandwidth. The half-power bandwidth of the linear energy harvester for a distance of 25 mm is 0.8 Hz only, which can be expanded to 2.67 Hz for the larger distance of 11 mm between magnets. The energy harvester presented in this work shows promising performances for broad-spectrum vibration excitations compared to conventional cantilever piezoelectric energy harvester systems with a tip mass.

Shape memory polymers (SMPs) are a class of active, deformable materials that can switch between a temporary shape, which can be freely designed, and their original shape. With their large deformation, low density, various stimulation methods, good biocompatibility and other advantages, SMPs have become widely accepted as smart materials. However, SMPs have many limitations and weaknesses that are exposed in engineering applications. For this reason, the significance of SMP composites (SMPCs) has been analyzed in terms of four aspects: reinforcement, innovation and improvement of driving methods, the creation of specific deformations and the creation of multifunctional materials. We then introduce the constitutive theory of SMPs and the post-buckling analysis of SMPCs. Afterward, we introduce the extensive applications of SMPCs in the fields of aerospace, biomedical equipment, self-finishing, deformable mandrels and the 4D printing of active origami structures, demonstrating their ability to undergo active driving and deformation, their adaptiveness, their ease of transport and their rapid production capacity, which fully demonstrate the unique advantages of SMPs in solving application problems. Finally, the advantages and disadvantages of SMPCs in applications are summarized, and the prospects for new SMPCs and new SMPC structures are described.

In this paper, a process for restoring damaged pipelines based on shape memory polymer composites (SMPC) was introduced, and the corrosion resistance and mechanical properties of SMPC were evaluated. First and foremost, SMPC was used for repairing damaged oil pipelines. Referring to the wet winding method, the subsidy pipe based on SMPC was fabricated by winding in the axial direction of ±45°. According to the failure theory of composite material, the minimum wall thickness of the subsidy pipe to withstand the pressure was determined. The effects of fiber content and temperature on the structural stiffness of semi-circular hinges with different ratios of carbon fiber were observed. Radial and axial compression tests were carried out on the subsidy pipe to study the effect of compression times and temperature on the stiffness. Radial compression tests are conducted on the subsidy pipes with different wall thicknesses to determine the effect of wall thickness on the stiffness.

Here, a co-extrusion-based 3D printing technology was applied to integrally manufacture continuous fiber reinforced composite trapezoidal corrugated sandwich structures (CFRCTCSs) with shape memory capability. The theoretical models were developed to analyze the bending performance and failure behavior of the 3D printed CFRCTCSs with various geometric configurations and verified by three-point bending tests. Good agreement between the predictions and the experimental measurements was achieved. Considering four dominant failure modes including face yielding, face buckling, core shear failure and indentation collapse, the failure maps based on the analysis models were constructed to highlight the failure mechanism of CFRCTCSs and provide a practical guide for the design of lightweight sandwich structures. Shape recovery tests were performed to confirm the shape memory capability of the 3D printed CFRCTCSs. Finally, the comparison of the bending properties with several competing structures indicates that the 3D printed CFRCTCSs possess the potential to provide new opportunities for lightweight systems and multifunctional applications.

Chiral-lattice metamaterials with unique mechanical, optical, electrical and magnetic properties have been widely used in many engineering applications, such as chiral recognition and separation, stealth materials and devices, as well as biological sensors. Various design strategies have been developed to obtain chiral-lattice metamaterials with different mechanical properties. The fast grown design strategies that can provide a variety of Poisson’s ratios and elastic moduli have brought new opportunities to emerging biomedical applications. In this study, hexagonal and tetragonal chiral-lattice metamaterials with positive and negative Poisson’s ratios were designed. The design strategy was based on a network structure with a periodic lattice topology, which was formed by three outer rings connected to the central ring via ligaments. The wide applications of this type of metamaterial were investigated via experiments and finite-element analysis. Demonstrative examples and the shape-memory effect (SME) suggest that the chiral-lattice structure has great potential in developing programmable metamaterials. The findings of this study provide essential guidance for the design of chiral network structures with the desired mechanical properties.

Mobile manipulators (MMs) performing the tasks of autonomous navigation, object grasp and transportation are widely used in industrial production and other domains. This paper presents a control system with multiple functions and good extendibility for a commonly configured MM, which controls the multi-degrees of freedom (DOF) movement of the MM while navigating, positioning, pose estimating and object grasp. This system has shown desirable control performance on an experimental platform.

This review is focused on the most recent research on multifunctional shape memory polymer nanocomposites reinforced by various nanoparticles. Different multifunctional shape memory nanocomposites responsive to different kinds of stimulation methods, including thermal responsive, electro-activated, alternating magnetic field responsive, light sensitive and water induced SMPs, are discussed separately. This review offers a comprehensive discussion on the mechanism, advantages and disadvantages of each actuation methods. In addition to presenting the micro- and macro- morphology and mechanical properties of shape memory polymer nanocomposites, this review demonstrates the shape memory performance and the potential applications of multifunctional shape memory polymer nanocomposites under different stimulation methods.