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Electrostatic layer jamming represents a lightweight, low energy consumption, electrically tunable, and cost-effective variable stiffness structure. Flexible parallel electroadhesive structures are the simplest form of electrostatic layer jamming. There is a lack of comprehensive and experimentally validated theoretical variable stiffness models of flexible parallel electroadhesive structures. Here we present the first variable stiffness model of flexible parallel electroadhesive structures under three-point bending, cantilever beam bending subjected to tip concentrated forces, and cantilever beam bending subjected to uniformly distributed forces, using the Euler–Bernoulli beam theory and considering friction and slip between layers by integrating the Maxwell stress tensor into the model. We find that: (1) three-point bending and cantilever beam bending under tip concentrated forces only have pre-slip and full-slip, whereas cantilever beam bending under uniformly distributed forces has an additional partial-slip which can be used for stiffness modulation; (2) the stiffness during the pre-slip stage is four times larger than the stiffness in the full-slip stage; and (3) increasing the voltage, dielectric permittivity, and coefficient of friction can elongate the pre-slip stage, thus enhancing the structural load capability. A customized three-point bending and a cantilever beam bending experimental setup were developed and the experimental deflection–force curve agreed relatively well with the theoretical one. The model, which considered electrode thickness and Young’s modulus, and the results presented in this work are useful insights for understanding the variable stiffness mechanism of electroadhesive layer jamming and are helpful for their structural optimization towards practical applications.

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.

Mars is believed to contain signs of the ancient life and to be the future of humankind. Deep space explorations on Mars have received extensive attention from the scientific and engineering communities. An ancient papyrus scroll-inspired mechanism to deploy the national flag after landing is proposed in this paper. Firstly, a papyrus scroll-inspired structure folded and deployed by shape memory polymer composites (SMPCs) was designed. The material was characterised by both thermodynamic analysis and static mechanical tests. Then, computational modal analysis was completed with material parameters at 25 °C, 55 °C and 85 °C to investigate the temperature effect. Besides, ground-based engineering validations were conducted, including vibration, shock and acceleration tests, as well as deployment verification. Natural frequencies obtained from vibration agreed well with that calculated from simulation. Regular and vacuum deployments showed differences but were both acceptable. Additionally, release reliability greater than 99.99% was obtained through repeated experimental data. Finally, on-Mars qualification was completed with China’s Tianwen-1 mission, with images of the deployed five-star red flag transmitted by the Zhurong rover. It is the world’s first validation of self-deployable mechanism based on SMPCs in deep space, and further applications can be expected.

Due to microscale fiber microbuckling, a fiber-reinforced soft composite demonstrates large macroscale bending deformation (e.g. 10% reversible macroscale compressive strain), which is larger than that of a convenient fiber-reinforced plastics (e.g. 1.5–2% elongation/compression at break). To investigate the deformation behavior, a normalized average energy density of a fiber-reinforced soft composite laminate was derived. By using a self-consistent approach according to the minimum energy principle, a series of analytical expressions were derived by a simplified theoretical method through solving simplified partial differential equations of average energy density. Furthermore, an improved numerical calculation method was developed using the full four terms of partial differential equations of average energy density by employing the results of simplified theoretical method as initial calculating values. The dimensionless results demonstrated that the trend correlated well between those two methods, and the improved numerical method obtained more accurate results than those of the simplified theoretical method. Analytical and numerical results in normalized expressions systematically descripted the bending large-deformation behavior including position of neutral surface and critical buckling, wavelength, amplitude, shearing strain, macroscale compressive/tensile strain, buckled fiber strain, and actuation moment. To design a fiber-reinforced soft composite for use in engineering, the simplified theoretical method is used to predict trend and obtain approximate results for preliminary design, and the improved numerical method is further used to check and obtain more accurate results on detailed design stage.

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.

Inspired by the accommodation mechanism of the human eye, several soft tunable lenses have been fabricated and demonstrated the capability of controllable focus tuning. This paper presents a computational model of a dielectric elastomer-based soft tunable lens with a compact structure that is composed of a lens frame, two soft films, and the optically transparent fluid enclosed inside. The two soft films, respectively, serve as the active film and passive film. The active film is a dielectric elastomer film and can be coated with the annular electrode or circular electrode. The deformation of the lenses with both electrode configurations can all be formulated by a boundary value problem with different boundary conditions and be solved as the initial value problem using the shooting method. Two common failure modes of loss of tension and electrical breakdown are considered in the calculation of the lens. The computational results can well fit the experimental data. The focus tuning performances as well as the distributions of stretches, stresses, and electric field in the active films of the lenses with two different electrode configurations are compared. The influences of several parameters on the performances of the lenses are discussed, such that the tunable lens can be designed to have maximum focal length change or to be optimized based on different application requirements.

Smart structures based on shape memory polymer composites (SMPCs) have attracted extensive attention because of their unique self-deployment behavior. This study investigated the thermal design and analysis of the SMPC flexible solar array system (SMPC-FSAS). The thermal design ensured the reliability of the deployment functionality and desirable structural temperatures. The fundamental properties of the shape-memory materials were obtained by dynamic mechanical analysis and shape fixity ratio tests. Thermal experiments, including the thermal balance test (TBT), thermal vacuum test and thermal cycle test were conducted to verify the safety and reliability of the SMPC-FSAS. Additionally, the temperature distribution of the SMPC-FSAS was simulated using numerical analysis. Notably, a geostationary satellite carrying the SMPC-FSAS was successfully launched into a geosynchronous orbit and controlled deployment was accomplished for the first time. The prediction of the numerical model was consistent with the TBT and on-orbit data, thus validating the accuracy of the numerical method. The research in this work has important reference significance for ultra-large SMPC-FSAS in the future.

Snap-through instability of viscoelastic materials is known to generate novel behavior, featured as pseudo-bistability, i.e. the capability of a system in maintaining a deformed configuration for a certain period of time after removal of an external load, followed by snapping back to its initial configuration automatically, due to the combination of time-dependent mechanical property and geometric nonlinearity of the system. This work numerically, experimentally, and analytically examines spherical viscoelastic domes with predesigned geometric imperfections that can control the structural stability and tune the snap time, which is defined as the time that a dome remains almost stationary in the deformed configuration after the release of external forces. The results show that even an imperfection with a small magnitude can play a significant role in pseudo-bistability. An imperfection with a positive amplitude shifts a viscoelastic dome towards bistable behavior, corresponding to a longer snap time, while an imperfection with a negative amplitude shifts the dome towards monostable behavior, resulting in a shorter snap time. This work can open up new opportunities for controlling spatiotemporal behavior of structures for multi-functionalities.

Shape memory polymer composite (SMPC) not only retains the unique stimuli-responsive ability of shape memory polymer (SMP), but also enhances the thermomechanical behavior of SMP. Although relatively complete thermal prediction models of SMPC have been established, the displacement jump due to interface damage has hardly been considered in these models. In this work, the thermomechanical constitutive model of SMPC considering the interface and micro-damage behavior is derived. The effective mechanical behaviors of SMPC under different temperatures and damage conditions are deduced by modifying Eshelby tensor and Mori-Tanaka method. Taking MWCNT/SMP composite as an example, the reliability of the model is verified by the thermomechanical coupling tests. More importantly, the model can also predict other reinforced types of SMPC by changing the configuration parameters and physical properties of the reinforcement phase.

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.

Shape memory polymers (SMPs) are novel intelligent materials. Evaluation of the durability of SMPs in the complex environment of future space applications helps to optimize their incorporation in space-deployable structures. In this paper, we performed vacuum outgassing and ultraviolet (UV) radiation exposure tests on a cyanate-based SMP with a glass transition temperature of 206 °C. The cyanate-based SMP shows 1.04% of total mass loss and 0.01% of collected volatile condensable matter, as determined by vacuum outgassing tests. Vacuum UV radiation deepened the color of the surface, shown little effect on the thermal stability of the SMP sample. The irradiation induced some instability of the molecular structure within the material, and this effect was gradually strengthened with the increase of exposure time. However, UV radiation did not detectably change the mechanical properties of the cyanate-based SMP; the tensile strength and elastic modulus remained essentially constant at 66 ± 2 MPa and 1940 ± 80 MPa, respectively. The average shape fixity rate and average shape recovery rate before and after UV radiation were all above 97.6%, and the repeatability was satisfactory.

As a new kind of smart material with shape changing and fixing abilities, the shape memory polymer (SMP), has become a research hotspot for space deployment structures in recent years. In fact, studying the space environmental adaptability of SMPs is an urgent research task, promoting their application in the aerospace field. In this study, a chemical crosslinked cyanate-based SMP (Tg~206°C) was exposed to atomic oxygen in a ground simulation system. The irradiation effects of atomic oxygen were investigated in terms of microscopic morphology, chemical structure, thermal stability, mechanical properties, loss factor and the storage modulus. After exposure to atomic oxygen, the cyanate-based SMP showed obvious surface erosion. When the irradiation dose reached 1022 atoms/cm2, the surface was entirely peeled off, and a new uneven surface emerged. However, the damage resulting from erosion was only on the surface and had little effect on the mechanical performance or shape memory behavior. The tensile strength and elastic modulus remained nearly constant at 66 MPa and 2000 MPa, respectively. Further, the effect of sample thickness and depth of delamination should be comprehensively considered in practical applications. The shape memory properties remain excellent after atomic oxygen irradiation, and the average shape fixity and shape recovery rates were 98.2% and 99.3%, respectively.

As a typical electroactive polymer, dielectric elastomer can be used in the research of actuators, sensors, and soft robots. The cone actuator, as a representative dielectric elastomer actuator, suffers from the limitation of deformation range. In this work, an antagonistic cone dielectric elastomer actuator with large deformation range is exhibited. A theoretical model is derived to design geometric parameters and explain the deformation mechanism of the antagonistic cone dielectric elastomer actuator. Comparison between theoretical and experimental results shows that the theoretical model is suitable for the prediction of the performance of the actuator. Inspired by the human heart, the pump is developed by the actuator, and its performance is systematically investigated through experiments. It is hoped that this work can play a guiding role in the development and application of the antagonistic cone dielectric elastomer actuator.

Multifunctional composites consist of Shape Memory Alloy and elastomer in the form of a hybrid system, in which every phase performs a different but necessary function. In this study, elastomer embedded with thermally responsive Shape Memory Alloy (SMA) wires forms one kind of multifunctional composites. The hyper elasticity of elastomer and reversing transformation temperature austenitic finish (Af) of SMA play highly complementary roles in achieving the multifunctional behavior. The composites show good in-plane deformation capability under the external force driving whether the temperature is under martensitic start temperature (Ms), or above austenitic finish temperature (Af) of SMA. The composites also show out-of-plane deformation ability under the external force driving when the temperature is under martensitic start temperatures (Ms) of SMA. Varying stiffness behaviors of the multifunctional composites can be obtained by changing the environment temperature from Ms. to Af, by which the grains of SMA wires could be switched from martensitic phase to austenitic phase. In this study, the varying stiffness characteristics of the SMA-elastomer composites are experimentally proved to be effective and theoretically investigated. Keywords: Elastomer, Shape Memory Alloy (SMA), Multi-function, Varying stiffness

Four-dimensional (4D) printing technology of continuous carbon fiber reinforced shape memory polymer composites is a potential manufacturing process for lightweight and high-strength intelligent composite structures. In this study, a 3D printer with dual feed channels based on the fused deposition modeling (FDM) was designed to fabricate continuous carbon fiber reinforced shape memory poly(lactic acid)-based composites (CFRSMPC). The impact of various printing parameters on the bending strength and flexural modulus of 4D printed CFRSMPC was evaluated by the three-point bending test. Meanwhile, mathematical prediction models of bending strength and modulus based on the existing experimental data were established. The electro-induced shape memory effect of 4D printed CFRSMPC was investigated by the electric heating shape recovery test. The shape recovery rate of the specimens was more than 95%, indicating that the resistance heating method is stable and feasible. The quantitative effect of bending angle and temperature on the resistance of CFRSMPC during the programming and recovery process was further investigated. The results demonstrated that the real-time deformation of the CFRSMPC could be monitored by the resistance measurement method. It can be concluded that the CFRSMPC fabricated using the 4D printing method can serve as potential building blocks for electrically activated and deployable structures.

Shape memory polymer composites (SMPCs) are gradually applied to deployable space structures due to their special shape memory effect and excellent mechanical properties. The design, material properties and performances of a smart hinge based on SMPC were investigated in this paper. The micro-buckling problem of the inner sheet of the hinge was solved by designing the bending path. The mechanical properties of materials with different fiber layers were characterized. The performance investigations began with obtaining the optimal voltage, followed by the test of the recovery speed, heat distribution and digital image correlation (DIC) for the SMPC hinge. The recovery force and deployed stiffness of the hinges with the different fiber layers followed by the observation of the variation of the surface morphology were obtained. The results indicated that the 3-layer hinge performed better than the 2-layer and 4-layer hinges in terms of deployed stiffness and surface morphology. Additionally, the strain variation of the hinge sheets was obtained. Finally, the smart hinge was assembled into the solar array prototype and the ground deployment verification test was successfully carried out. The research results of the hinge are expected to have reference significance in deployable space structures.

4D printing provides more design freedom for the static structures by adding time dimension in 3D printing. In recent years, some types of active origami structures fabricated by 4D printing have been developed, but most of these structures were thin sheets, which may lead to poor mechanical properties of the structures. In this work, honeycomb sandwich structures were designed to improve the stiffness and recovery force of origami structures. The in-plane tension, in-/out-plane three-point bending, recovery force and shape memory performances of the sandwich structures were investigated. The shape fixity and shape recovery ratio of the active sandwich structures were 98% and 99%, indicating excellent shape memory performance. The application of the sandwich structures in thermally activated self-deployment origami structures was verified. These developed origami structures have the advantages of large area change ratio and fast response speed, demonstrating the great application prospects in the space deployable structures such as antennas.

During the service of shape memory polymer (SMP), the thermal-mechanical cycle is a necessary process. Meanwhile, the influence of the viscoelastic properties of SMP, such as rate-dependent behaviors, can not be ignored during the application. Consequently, a constitutive model based on the multiplicative decomposition of the deformation gradient is proposed in this work, which can clearly describe the viscoelastic behavior and capture the thermal-mechanical cycle process of SMP. By introducing the “phase transition” concept, SMP is assumed as a composite composed of glassy phase and rubbery phase, and the volume fractions of each phase vary with temperature. Furthermore, according to the different mechanical behaviors of the glassy phase and rubbery phase, two different constitutive structures that can describe the strain sensitivity of SMP are developed to represent the mechanical response. The developed model was verified by simulating a series of experiments, including strain sensitivity tests and thermal-mechanical cycle experiments.

A micromechanics model based on thermal viscoelasticity constitutive relation is presented to investigate the thermal-mechanical behavior of particulate reinforced shape memory polymer composite (SMPC). Based on the thermomechanical constitutive relation assumption and linear elastic constitutive relation assumption, the effective properties of SMPC are studied by using a micromechanics method. Through analyzing the constitutive theories of polymer and multi-walled carbon nanotubes (MWCNTs), as well as the filling quality of particles, the generalized Maxwell model (GMM) combined with Mori-Tanaka theory is developed, and the thermo-mechanical cycle behavior of SMPC is studied emphatically. Moreover, a set of uniaxial tensile experiments, stress relaxation tests and thermal-mechanical cycle tests are performed to verify the developed model. Eventually, the developed model is validated using a simulated example and experiment to ensure its creditability.

Dielectric elastomer (DE) is a promising electroactive polymer. As DE material, rubbers are often filled with functional particles to improve their electromechanical performance. However, the filled particles also bring stress softening, which is known as Mullins effect. In this paper, we prepared the carbon nanotube filled silicone elastomer (SE) as DE composite and modeled its Mullins effect using the pseudo-elastic theory. Then, the thermodynamics of DE was combined to predict the idealized electromechanical softening behavior. Two cases are considered: linear dielectric and saturated dielectric. For linear dielectric with an initial force, “residual strain” will appear after every voltage-controlled cycle, and instability may be eliminated in reloading. For saturated dielectric, the material response changes a lot after saturation, which also affects the subsequent softening behavior. At last, viscoelasticity was further incorporated to account for rate-dependent softening deformation, and we also carried out some simple electromechanical experiments on VHB 4910 to explore its softening behavior. This work may lead to a better understanding of the softening behavior in DEs undergoing electromechanical coupling situations.

As a kind of intelligent material, shape memory polymer (SMP) can respond to outside stimuli and possesses good properties including shape memory effect, deformability and biological compatibility, etc. SMPs have been introduced for medical applications such as tissue engineering, biological sutures, stents and bladder sensors. Due to the shape memory effect, the medical devices based on SMP can be implanted into body through minimally invasive surgery in contraction or folded state and recovered to their requisite original shapes at target position. In this paper, a review of SMPs utilized in biomedical applications and their actuation methods are listed. Various biomedical applications and potential applications based on the beneficial properties of SMP are also summarized.

Experiments are conducted to test the permittivity of dielectric elastomer composites adulterated with multi-walled carbon nanotube (MWCNT). The results show that the permittivity of dielectric elastomer composites can be significantly improved by adding MWCNT conductive particles. A thermodynamic model is presented to investigate the stability of MWCNT particle-doped dielectric elastomer composites. The theoretical investigation proves that the polarization of MWCNT, the electrostriction deformation and material constants of the elastomer significantly affect the stability of the thermodynamic system. The numerical analysis shows that comparing to ideal dielectric elastomer, the stability of dielectric elastomer composites filled with MWCNT coupling between electrostriction and polarization can be significantly enhanced.

Dielectric elastomer is a kind of typical electro-active polymer material. Under external electric field it can produce large electrostriction deformation and possesses the advantages of high elastic energy density, super short response time, high efficiency, and so on. It is widely used in the artificial muscles, facial expressions, actuators, energy harvesters, sensors, robots and Braille display devices, and also shows huge application potential in the aerospace and intelligent bionic areas. We built the free energy of the dielectric elastomer electrical-mechanical coupling system and investigated its constitutive relation and stability behavior. Then we calculated the elastomer’s critical deformation suffering from the voltage. If electrical breakdown, electromechanical instability and snap-through instability can be avoided, the large electrostriction deformation can induce adiabatic temperature change and isothermal entropy change of the dielectric elastomer. We used the entropy-temperature or electric displacement-electric field plane to describe the temperature change and entropy change of dielectric elastomer undergoing large electrostriction deformation. With the influence of temperature, we developed a temperature and deformation coupling thermodynamical free energy model to calculate the electric field induced variation of temperature and entropy in dielectric elastomers. The results should offer great help in guiding the design and fabrication of excellent actuators featuring soft dielectric elastomers.

The ever increasing applications of Shape Memory Polymers (SMPs) and its Composites (SMPCs) have motivated the development of appropriate constitutive models. In this work, based on composite bridging model, a constitutive model for unidirectional SMPCs under thermal mechanical loadings in the small strain range has been developed. The composite bridging model has been adopted to describe the distribution of stress–strain between fiber reinforcement and SMPs matrix. Besides, considering the influence of fiber content and temperature, the storage and release of “frozen strain”, the recovery of stress has been quantified as well. The stress–strain curves of SMPCs laminate under axial tensile indicate that the theoretical data derived from the developed model are basically accordant with the experimental data, and that the proposed model is suitable for machining practice. Furthermore, the model has been applied to predict stress recovery, strain storage and releasing with changing of temperature.

In this paper, the influence of both temperature and deformation on dielectric constant is considered during the establishment of free energy function of dielectric elastomers. A constitutive model of the thermodynamic systems undergoing adiabatic process is derived to study its thermoelectromechanical stability. The relations between different work conjugated parameters of dielectric elastomer are theoretically described, including the relations between nominal electric field and nominal electric displacement, entropy and temperature. Under different temperatures and electric fields, the allowable energy range of dielectric elastomer is calculated. Furthermore, the electric-induced variation of dielectric elastomer’s temperature and entropy is also studied under various principal planar stretch ratios. These simulation results should offer assistances in guiding the design and fabrication of excellent actuators featuring dielectric elastomers.

Single-walled carbon nanotubes (SWNTs) have been introduced as compliant electrodes for dielectric elastomers (DEs) due to fault tolerance. To acquire a better electrostrictive strain and longer lifetime, it is essential to obtain a certain and uniform width of the SWNT electrode. To ensure uniform width manually, a small flux and longer time are necessary. Moreover, it is difficult to control the width of the electrode for the randomness of manual spraying. Therefore, a new type of automatic spraying process is presented in this paper. The width and homogeneity of the electrode can be easily controlled by certain parameters of the process. Two methods for detecting the homogeneity of the electrode are introduced in this paper: Measurement of surface resistance and luminosity. The coefficient of variation (CV) values detected by the two methods are virtually equal and less than 8%, which shows the feasibility of the detection method and homogeneity of automatic spraying. The speed of automatic spraying is 102 mm2/s, which is higher than that of manual spraying. The spraying process and the method used to detect homogeneity in this paper provide a reference for the relevant processes.

Based on the thermomechanical mechanism of shape memory polymers (SMPs), the three-dimensional thermomechanical constitutive equation that can be used in the ABAQUS finite element simulation was derived. Then this paper compiled UMAT subroutine and simulated the thermomechanical behaviors of SMP smart mandrels. In addition, the properties of shape fixity and shape recovery ratio of SMP were considered in detail. Finally, filament winding experiments were proceeded on bottle-shaped and air duct-shaped mandrels and the simple and efficient demoulding of SMP mandrels were verified. The results showed the feasibility of SMP as the smart mandrels from practical application in the future.

The alternation of temperature and entropy induced by an electric field in a polar dielectric material is known as the electrocaloric effect (ECE). This paper develops a thermodynamic theory of the polar elastic dielectric with large ECE and large deformation compatibility. The theory characterizes the equilibrium condition of the polar elastic dielectric which is subjected to mechanical forces, electric field and thermal field. The mechanical behavior and large deformation of the polar elastic dielectric thermo-electro-mechanical system are analyzed under the coupling influence of hyperelastic, polarization, electrostriction and thermal contribution on the system. The typical thermodynamics cycles of the polar elastic dielectric are described as cooling devices and generators and the electrocaloric and pyroelectric energy conversion are calculated. Ferroelectric polymer, as an important category of electroactive polymers, is a typical polar dielectric with a large ECE and a large deformation. As an example, when subjected to different voltage, the ferroelectric polymers are regarded as cooling devices. We calculated their temperature change, entropy change, heat absorptions and work generation. We also calculated the voltage change, electric quantity change and work of the ferroelectric polymer which is regarded as generators when subjected to different temperatures. Finally, we investigated the thermo-electro-mechanical coupling behavior of the ferroelectric polymers undergoing ferroelectric–paraelectric phase transition.

A segmented styrene-based shape memory polymer (SMP) comprising two types of SMP materials (S1-SMP and S2-SMP) was fabricated by using a two-step curing method to exhibit the triple shape memory effect (triple-SME). The material properties of S1-SMP and S2-SMP parts were explored using dynamic mechanical analysis, multi-frequency scan testing, thermal expansion measurements, static tensile testing and shape memory testing, respectively. Meanwhile, the triple-SME of segmented SMP was also characterized by shape memory testing with continue heating step. These experimentally determined material properties were incorporated into the theoretical model for the triple-SME based on a phase transition model and Generalized Maxwell model. Experimental verification was obtained by observing the triple-SME behavior under uniaxial tensile strain of 20%. Finally, the triple-SME behavior of SMP was assessed in two engineered implementations; a programmable self-deployed structure model and double bottle-shaped smart mandrel. Good agreement was demonstrated between experimental result and a finite-element model (FEM) simulation during the continue heating recovery step.

Smart materials that change their properties in response to external stimuli are of interest for emerging application in energy harvesting. Here, we employ the facile thermal condensation method to synthesize flexible carbon nitride films that can convert slight variations in surrounding humidity to multiple distinct deformations. A quick jumping motion is generated in response to sudden increases in humidity, whereas subtle changes in humidity (i.e., an increase of 2%) cause the film to change shape from tubular to arched. When exposed to humidity fluctuations, the film moves forward by about 2 mm. These results show the prepared carbon nitride film has a great potential in water-driven generators.

As a new kind of smart materials, shape memory polymer composites (SMPCs) are being used in large in-space deployable structures. However, the recovery force of pure SMPC laminate is very weak. In order to increase the recovery force of a SMPC laminate, an alloy film was bonded on the surface of the laminate. This paper describes the post bulking behavior of the alloy film reinforced SMPC laminate. The energy term associate with this in-plane post buckling have been given .Based on the theorems of minimum energy, a mathematical model is derived to describe the relation between the strain energy and the material and geometry parameters of the alloy film reinforced SMPC laminate. The finite element model (FEM) is also conducted to demonstrate the validity of the theoretical method. The relation between the recovery force and the material geometry parameters were also investigated. The presented analysis shows great potential in the engineering application such as deployment of space structures.

This paper summarizes the research progress of dielectric elastomer (DE) and its composite materials, including the introduction of materials, theoretical research development, and typical applications. First of all, the DE composite materials are introduced. Then, the theoretical research development of DEs is summarized. Finally, some applications as well as research prospects about DEs are listed.

By applying a voltage, electric charge will be induced on the surface of dielectric elastomers. Generally, the charge increases with the level of voltage. When the voltage reaches to a certain value, the charge would not increase any more due to the polarization saturation of dielectric materials. In this paper, a thermodynamic constitutive model, combined both the nonlinear dielectric and hyperelastic behavior as dielectric elastomers undergoing polarization saturation, has been developed. Analytical solutions have been obtained for situations incorporating strain-stiffening effect, electromechanical instability and snap-through instability. The numerical results reveal the marked influence of the extension and polarization saturation limits of elastomer material on its electromechanical instability and the snap-through instability. The developed constitutive model would be helpful in future research of dielectric elastomer based high-performance transducers.

A dielectric elastomer is capable of large voltage-induced deformation, particularly when the voltage is applied on the verge of snap-through instability. A model is described which shows that the snap-through instability is markedly affected by both the extension limit of polymer chains and the polarization saturation of dipoles. The model may guide the search for high-performance dielectric elastomer transducers.

Dielectric elastomer (DE) balloon is a new type of actuator that can be used as high frequency pumps or loudspeakers. In this paper, a theoretical model of DE balloon, incorporating stiffening and damping effect, is developed. The numerical results, such as stretch–time curves, phase diagrams and Poincare maps, are presented to study the influence of stiffening and damping on its dynamic performance. Taking the damping effect into account, the DE balloon can reach the equilibrium state after attenuation when subject to an instantaneous constant voltage; subject to a ramping voltage, the dynamic response presents three obvious stages: steady deformation, snap-through or snap-back, and damped oscillation. Due to the strain stiffening, the DE balloon may have two different stable equilibrium states and each has its own natural frequency. With small perturbation energy, the DE balloon can oscillate steadily around the two equilibrium states and resonate at multiple excitation frequencies. With large perturbation energy, the steady oscillation may transform into chaos. The damping force, however, changes no matter steady or chaotic oscillation into a constant periodic oscillation, and also determines the oscillation position.