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As a typical smart material, shape memory polymers (SMPs) have the capability of variable stiffness in response to external stimuli, such as heat, electricity, magnetism and solvents. In this research, a shape memory polymer composite (SMPC) tube composed of multi-layered filament wound structures is investigated. The SMPC tube possesses considerable flexibility under high temperature and rigidity under low temperature. Significant changes in effective engineering modulus can be achieved through regulating the environment temperature. Based on the classical laminated-plate theory and Sun's thick laminate analysis, a 3D theory method is used to study the effective engineering modulus and modulus ratio of the SMPC tube. The tensile test is conducted on the SMPC tube to verify the accuracy of the theoretical method. In addition, the effective engineering modulus and modulus ratio are discussed under different fiber-winding angles and fiber volume fractions of the SMPC tube. The presented analysis provides meaningful guidance to assist the design and manufacture of SMPC tubes in morphing skin applications. [ABSTRACT FROM AUTHOR]

When a dielectric elastomer (DE) tube is subjected to mechanical pressure and electrical voltage, electromechanical (EM) phase transition may happen. In recent experiment, it has been shown that the EM phase transition process can be highly time-dependent: the bulged section can propagate along the tube under fixed voltage. In this article, we adopt a nonlinear viscoelastic model for the DE material to investigate the time-dependent EM phase transition of a DE tube under fixed amount of air and fixed voltage. Using the model of viscoelasticity, we demonstrate that a DE tube may experience a transition from a homogeneous shape to an inhomogeneous shape with bulged and unbulged sections coexisting in the tube under electrical loading, then the bulged section can gradually propagate at the expense of the unbulged section under the fixed initial coexistent voltage, which well captures the experimental observations. We have further shown that the EM phase transition condition and propagation of the bulged section of the DE tube also depend on the volume of the air chamber connected to the tube and the ramping rate of the applied voltage. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Shape memory polymers and their composites are kind of smart materials, which can transfer from the temporarily fixed configuration to the original configuration under external stimuli. Their inherent advantages are low density, low cost, large recoverable deformation ability and controllable stimulus method, which make them an alternative for aerospace applications (deployable structures, release devices, wrinkled/slack control component, etc). Most of these applications are in development stage, some have completed the ground functional verification experiments, a rare part has been carried out the spaceflight experiments. This review focuses on their materials and structures in aerospace field, briefly introduces the development history and general mechanism of shape memory polymers and their composites, replenishes the space radiation resistance abilities of these materials under the ground-simulated space radiation experiments, tracks those applications who have already completed the spaceflight experiments, then exhibits some novel applications which have great potential and could give us inspirations for new aerospace application development, finally the prospects for materials and structures are discussed in the future outlook. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) as a kind of functional material have attracted great attention in aerospace field. High temperature resistant, high mechanical strength and space environment resistant materials are needed in practical applications. In this paper, the cyanate ester resin with a high glass transition temperature 219.4 °C and a high storage modulus 2.14 GPa was fabricated. The effect of different dose of γ-rays radiation on shape memory cyanate ester (SMCE) resin was investigated. Compared to the SMCE resin, the storage modulus of the irradiated SMCE who underwent 1000 KGy radiation increased 2.6% and the stretching strain exceeded 44.5%. The shape recovery rate of SMCE reached up to 99.6% and that of the irradiated SMCE is 98.8%. Moreover, carbon fiber fabric reinforced cyanate-based composites were prepared via a sandwich mold perfusion method for increasing resin’s strength and load, whose shape recovery time was shorter than that of SMCE. Thermosetting SMPs and their composites with high transition temperature and good irradiation resistance performances is expected to play an important role on spacecraft in the future. [ABSTRACT FROM AUTHOR]

A sunlight-stimulated substrate, named Mission SMS-I, carried out the orbital deployment experiment and anti-irradiation verification on an experimental geostationary satellite. It is the prototype of a solar array substrate which integrates the conventional substrate, support structure, and deployment function by using the carbon fabric reinforced shape memory polymer composite (SMPC). The substrate could deploy from the ‘Ω’ packaged configuration to the ‘-’ deployed configuration once its temperature is at or above the glass transition temperature. This paper presents details of the Mission SMS-I in a sequence of material preparation, structure design, manufacture, ground experiments, and orbital experiment. Results show that the Mission SMS-I can withstand the required mechanical and thermal conditions, successfully deploy in orbit and have a good long-term anti-irradiation capability. SMPC is a suitable choice for the substrate of solar arrays or any other deployable structures which need the actuation in material-level or directly exposed to the space environment. [ABSTRACT FROM AUTHOR]

Colorless shape memory polyimide (CSMPI) has potential applications in broad fields, especially in advanced optoelectronics due to the excellent optical transparency, shape memory effect and high temperature resistance. In this work, high flexible dianhydrides and fluorine-containing diamines were used to synthesize CSMPI, which simultaneously combined great shape memory performance with high optical transparency. The effects of monomer ratios and imidization temperatures on the molecular structure and properties were investigated. Moreover, the CSMPI film possesses a higher glass transition temperature (Tg) of 234 °C, compared with the reported transparent shape memory polymers. Most importantly, the transmittance of CSMPI film is 87%–90% at 450–800 nm, meeting the requirements of heat resistance and transmittance of the substrate. Both shape recovery and shape fixity are over 97%. Flexible and colorless CSMPI films severed as substrates provide more potential in optoelectronic devices such as OLED and OPV, etc. [ABSTRACT FROM AUTHOR]

A shape memory light-induced microfluidic technology is applied in preprogrammed microfluidic chip based on shape memory gold nanoparticles/poly (vinyl alcohol) nanocomposites. The shape memory gold nanoparticles/poly (vinyl alcohol) nanocomposites display excellent light-induced shape memory property with recovery ratio of nearly 100% in visible light. The crosslinked network of light-induced shape memory gold nanoparticles/poly (vinyl alcohol) nanocomposites forms by aldol reaction, esterification, and/or hydrogen bonding of poly (vinyl alcohol), glutaraldehyde, and gold nanoparticles. The light-induced shape memory mechanism of shape memory gold nanoparticles/poly (vinyl alcohol) nanocomposites is based on photothermal effect of gold nanoparticles and shape memory effect of poly (vinyl alcohol)-based shape memory polymer (SMP). In this report, a light-induced microfluidic microvalve is demonstrated based on the shape memory gold nanoparticles/poly (vinyl alcohol) nanocomposites. This research presents demonstration of the shape memory light-induced intelligent microfluidic chip. The light-induced SMP microfluidic microvalve would yield practical, physical, and technological advantages for disposable integrated microfluidic chip laboratories. [ABSTRACT FROM AUTHOR]

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 Poincaré 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. [ABSTRACT FROM AUTHOR]

This paper focuses on a smart transmission mechanism system, designed and fabricated based on compliant mechanisms. The system was assembled using a piezo-stack actuator in conjunction with a rhombus-type amplifier, a novel transmission mechanism synthesized with flexure hinges, and an active rotatable flap. This assembly is able to be utilized in smart structures to dynamically transfer linear motion generated from some actuators to rotational motion of active rotatable flaps from a long distance at a wide range of frequencies (1 Hz ∼ 64 Hz). The Lagrangian approach was utilized for dynamic analysis of the system to evaluate the fundamental natural frequency of the smart transmission mechanism system, and the result is 385 Hz; the error is 9% compared with a finite element analysis using ANSYS. Then force and displacement transmissibility of the system was also theoretically calculated based on a newly established theoretical model, and the detailed finite element analysis was also performed to study these properties. A prototype of the smart transmission mechanism system and a special test platform were manufactured to test the force and displacement transmissibility then the transmissibility was experimentally tested. The theoretical and numerical results found a good correlation with the experimental results, and the errors between experimental and theoretical (or numerical) results are within 13% (or 11%). The newly designed transmission mechanism system and the corresponding theoretical, numerical and experimental studies are able to direct the optimal design of some smart systems which consist of compliant mechanisms and transmission mechanisms. They can also offer fundamental information on the active vibration control using some piezo-stack actuators to actuate active flaps. [ABSTRACT FROM AUTHOR]

Shape memory polymers with high glass transition temperature (HSMPs) and HSMP-based deployable structures and devices, which can bear harsh operation conditions for durable applications, have attracted more and more interest in recent years. In this article, colorless and transparent shape memory polyimide (SMCTPI) films were subjected to simulated vacuum thermal cycling, atomic oxygen (AO) and ultraviolet (UV) irradiation environments up to 600 h, 556 h and 600 h for accelerated irradiation. The glass transition temperature (Tg) determined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) had no obvious changes after being irradiated by varying amounts of thermal cycling, AO and UV irradiation dose. After being irradiated by 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, shape recovery behaviors of SMCTPI films also had no obvious damage even if they experienced 30 shape memory cycles, while the surface morphologies and optical properties were seriously destroyed by AO irradiation, as compared with thermal cycling and UV irradiation. The tensile strength could separately maintain 122 MPa, 120 MPa and 70 MPa after 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, which shows great potential for use in aerospace structures and devices. [ABSTRACT FROM AUTHOR]

This work presents a variable stiffness corrugated structure based on a shape memory polymer (SMP) composite with corrugated laminates as reinforcement that shows smooth aerodynamic surface, extreme mechanical anisotropy and variable stiffness for potential morphing skin applications. The smart composite corrugated structure shows a low in-plane stiffness to minimize the actuation energy, but also possess high out-of-plane stiffness to transfer the aerodynamic pressure load. The skin provides an external smooth aerodynamic surface because of the one-sided filling with the SMP. Due to variable stiffness of the shape memory polymer the morphing skin exhibits a variable stiffness with a change of temperature, which can help the skin adjust its stiffness according different service environments and also lock the temporary shape without external force. Analytical models related to the transverse and bending stiffness are derived and validated using finite element techniques. The stiffness of the morphing skin is further investigated by performing a parametric analysis against the geometry of the corrugation and various sets of SMP fillers. The theoretical and numerical models show a good agreement and demonstrate the potential of this morphing skin concept for morphing aircraft applications. We also perform a feasibility study of the use of this morphing skin in a variable camber morphing wing baseline. The results show that the morphing skin concept exhibits sufficient bending stiffness to withstand the aerodynamic load at low speed (less than 0.3 Ma), while demonstrating a large transverse stiffness variation (up to 191 times) that helps to create a maximum mechanical efficiency of the structure under varying external conditions. [ABSTRACT FROM AUTHOR]

Shape memory polymer (SMP) is a new kind of intelligent polymer, which can be activated by an external stimulus to change and subsequently recover its original shape. Due to this shape memory effect, SMP can be used in a wide range of engineering and biomedical applications. This paper details an application of SMP on manufacturing of a fracture fixation. The basic properties were characterized by dynamic mechanical analysis, and the stress relaxation and fatigue were established. An SMP-based fracture fixator was designed, analyzed, and optimized. Finally, the fixator was fabricated and the fixed effects were verified by experiment in vitro. The performance of the SMP-based fixator was excellent and proved to be a potential replacement for the traditional fracture fixator. [ABSTRACT FROM AUTHOR]

Shape memory polymer foam is a promising kind of structure in the biomedical and aerospace field. Shape memory styrene foam with uniform and controlled open-cell structure was successfully fabricated using a salt particulate leaching method. Shape recovery capability exists for foam programming in both high-temperature compression and low-temperature compression (g) in the deformation processes. Such a property could expand its potential application in the self-healing field. The mechanical property at different temperatures was thoroughly studied. Shape recovery properties such as shape fixing property and shape recovery ratio were also characterized. In order to provide guidance for the future fabrication of shape memory foam, the theories of Gibson and Ashby as well as differential micromechanics theory were applied to predict Young’s modulus and the mechanical behavior of SMP styrene foams during the compression process. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) have the ability to adjust their stiffness, lock a temporary shape, and recover the permanent shape upon imposing an appropriate stimulus. They have found their way into the field of morphing structures. The electrically Joule resistive heating of the conductive composite can be a desirable stimulus to activate the shape memory effect of SMPs without external heating equipment. Electro-induced SMP composites incorporated with carbon fiber felt (CFF) were explored in this work. The CFF is an excellent conductive filler which can easily spread throughout the composite. It has a huge advantage in terms of low cost, simple manufacturing process, and uniform and tunable temperature distribution while heating. A continuous and compact conductive network made of carbon fibers and the overlap joints among them was observed from the microscopy images, and this network contributes to the high conductive properties of the CFF/SMP composites. The CFF/SMP composites can be electrical-heated rapidly and uniformly, and its’ shape recovery effect can be actuated by the electrical resistance Joule heating of the CFF without an external heater. The CFF/SMP composite get higher modulus and higher strength than the pure SMP without losing any strain recovery property. The high dependence of temperature and strain on the electrical resistance also make the composite a good self-sensing material. In general, the CFF/SMP composite shows great prospects as a potential material for the future morphing structures. [ABSTRACT FROM AUTHOR]

The present study reports a feasible approach of fabricating shape memory composite foams with an interpenetrating polymer network (IPN) based on polyurethane (PU) and shape memory epoxy resin (SMER) via a simultaneous polymerization technique. The PU component is capable of constructing a foam structure and the SMER is grafted on the PU network to offer its shape memory property in the final IPN foams. A series of IPN foams without phase separation were produced due to good compatibility and a tight chemical interaction between PU and SMER components. The relationships of the geometry of the foam cell were investigated via varying compositions of PU and SMER. The physical property and shape memory property were also evaluated. The stimulus temperature of IPN shape memory composite foams, glass temperature (Tg), could be tunable by varying the constituents and Tg of PU and SMER. The mechanism of the shape memory effect of IPN foams has been proposed. The shape memory composite foam with IPN developed in this study has the potential to extend its application field. [ABSTRACT FROM AUTHOR]

A novel and facile strategy was proposed to construct a thermosetting/thermoplastic system with both shape memory and self-healing properties based on commercial epoxy resin and poly(ϵ-caprolactone)-PCL. Thermoplastic material is capable of re-structuring and changing the stiffness/modulus when the temperature is above melting temperature. PCL microfiber was used as a plasticizer in epoxy resin–based blends, and served as a ‘hard segment’ to fix a temporary shape of the composites during shape memory cycles. In this study, the electrospun PCL membrane with a porous network structure enabled a homogenous PCL fibrous distribution and optimized interaction between fiber and epoxy resin. The self-healing capability is achieved by phase transition during curing of the composites. The mechanism of the shape memory effect of the thermosetting (rubber)/thermoplastic composite is attributed to the structural design of the thermoplastic network inside the thermosetting resin/rubber matrix. [ABSTRACT FROM AUTHOR]

In the last few decades, shape memory polymers have demonstrated their major advantages of extremely high recovery strain, low density and low cost. Generally, the mechanical behavior of shape memory polymers is strongly dependent on the loading strain rates. Uniaxial tensile experiments were conducted on one kind of typical shape memory polymer (epoxy) at several different temperatures (348 K, 358 K, 368 K and 378 K) and true strain rates (0.25% s−1, 1.25% s−1 and 2.5% s−1). Thus, the influence of strain rate and temperature on the mechanical behavior of epoxy, in particular on the post yield stresses and the strain hardening behavior, were investigated through this experimental study. Based on our previous work Guo (2014 Smart Mater. Struct.23 105019), a simplified model which can explain the shape memory effect of epoxy was proposed to predict the strain hardening behavior of the shape memory polymer. Based on the suggestion of Rault (1998 J. Non-Cryst. Solids235–7 737–41), a linear compensation model was introduced to indicate the change in yield stresses with the increase of strain rate and temperature. Finally, the new model predictions for the true strain and stress behavior of epoxy were compared with the experimental results. [ABSTRACT FROM AUTHOR]

In this study, one kind of developed morphing skin embedded with pneumatic muscle fibers (PMFs) was manufactured and was employed for camber morphing structures. The output force and contraction of PMF as well as the morphing skin were experimentally characterized at a series of discrete actuator pressures varying from 0.15 to 0.35 MPa. The active morphing skin test results show that the output force is 73.59 N and the contraction is 0.097 (9.7%) at 0.35 MPa. Due to these properties, this active morphing skin could be easily used for the morphing structures. Then the proper airfoil profile was chosen to manufacture the adaptive airfoil in this study. The chord-wise bending airfoil structure was achieved by employing this kind of active morphing skin. Finally the deformed shapes of this chord-wise bending airfoil structure were obtained by 3-dimensions scanning measurement. Meanwhile the camber morphing structures were analyzed through the finite element method (FEM) and the deformed shapes of the upper surface skins were obtained. The experimental result and FEM analysis result of deformed shapes of the upper surface skins were compared in this paper. [ABSTRACT FROM AUTHOR]

This paper describes a new concept of an active honeycomb structure for morphing wingtip applications based on tubular inflatable systems and an auxetic cellular structure. A work-energy model to predict the output honeycomb displacement versus input pressure is developed together with a finite element formulation, and the results are compared with the data obtained from a small-scale example of an active honeycomb. An analysis of the hysteresis associated with multiple cyclic loading is also provided, and design considerations for a larger-scale wingtip demonstrator are made. [ABSTRACT FROM AUTHOR]

Recently, increasing applications of shape memory polymers have pushed forward the development of appropriate constitutive models for smart materials such as the shape memory polymer. During the heating process, the phase transition, which is a continuous time-dependent process, happens in the shape memory polymer, and various individual phases will form at different configuration temperatures. In addition, these phases can generally be divided into two parts: the frozen and active phase (Liu Y et al 2006 Int. J. Plast.22 279–313). During the heating or cooling process, the strain will be stored or released with the occurring phase transition between these two parts. Therefore, a shape memory effect emerges. In this paper, a new type of model was developed to characterize the variation of the volume fraction in a shape memory polymer during the phase transition. In addition to the temperature variation, the applied stress was also taken as a significant influence factor on the phase transition. Based on the experimental results, an exponential equation was proposed to describe the relationship between the stress and phase transition temperature. For the sake of describing the mechanical behaviors of the shape memory polymer, a three-dimensional constitutive model was established. Also, the storage strain, which was the key factor of the shape memory effect, was also discussed in detail. Similar to previous works, we first explored the effect of applied stress on storage strain. Through comparisons with the DMA and the creep experimental results, the rationality and accuracy of the new phase transition and constitutive model were finally verified. [ABSTRACT FROM AUTHOR]

We here propose a new method to analyze the thermo-electro-mechanical instability of dielectric elastomers. The equilibrium equations in this thermodynamic system at different temperatures are initially established. We then obtained the critical nominal electric field and the critical stretch under various mechanical and thermal loads, involving the effects of different stretch regimes on the system stability, i.e. the equal-biaxial stretch, the unequal-biaxial stretch and the thickness elongation. Finally, numerical results showed that as the temperature increases, the critical nominal electric field and the stretch of the dielectric elastomer are strengthened, which consequently stabilize the system. The results provide guidance to the design and synthesis of dielectric elastomer-based devices, especially for those operating at various temperatures. [ABSTRACT FROM AUTHOR]

For the thermal response of shape-memory polymer (SMP) it has been experimentally demonstrated that the actuation can be achieved using interactive solvent. In this paper, the effect of the solubility parameter of the interactive solvent on the shape recovery behavior and glass transition temperature of polystyrene SMP was investigated experimentally. The effect of the solubility parameter on the activation energy was separated and qualitatively identified, as expected from the relaxation theory and Eyring equation. This approach should be applicable to other SMPs and their composites and many extension applications and achievements could be based on this outcome. [ABSTRACT FROM AUTHOR]