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The process of repeating shape memory cycle of the shape memory foam whose initial structure is nonauxetic is more complex. In this cases, only one-shot deformation, which will greatly limit the application of this smart metamaterial. Thus, in this study, we report a feasible approach of fabricating the original structure of shape memory foams with auxetic property based on second curing method. The commercial soft polyurethane foam material and shape memory epoxy resin was used in fabricating the shape memory auxetic foam. Polyurethane component plays role in the similar function of “auxetic mold,” while shape memory polymer act as fixing auxetic structure of foam. The negative Poisson’s ratio was achieved around −0.22. Tunable foam mechanical property was demonstrated by structural control according to its shape memory property. The functional filler was employed to realize the wireless actuation of auxetic foam. The excellent shape memory properties have been achieved as well. The combination of smart materials and metamaterial structure makes it have excellent structural mechanical properties and intelligent properties of materials, which greatly expands their potential application prospects.

Shape memory polymers (SMPs) are a class of smart materials with large deformation performance and variable stiffness characteristics, and have exhibited great potential in morphing skins. The thermal stimulation of SMPs is one of the hotspots in recent years. Shape memory polymer composites (SMPC) filled with conductive materials are activated by Joule heating without external heating facilities. The existing electro-induced SMPCs filled with conductive materials would limit large tension deformation, cannot be heated in a large area, or damage the heating circuit under cyclic loading. These aspects restrict the application of SMPC for morphing skins. In this work, an electro-induced SMP composite was fabricated by the styrene-based SMP incorporated with conductive elastic fabric (CEF) to remove the limiting factors as much as possible. The thermos-mechanical properties and electro-active characteristics of CEF/SMP composite were systematically investigated. The maximum strain at break of CEF/SMP composites reached 206% at 80°C, exhibiting excellent deformation performance. The resistance remained relatively stable after 50 cycles under 40% tensile strain. Furthermore, the CEF/SMP composite with a dimension of 160×160×3 mm3 was successfully heated above the glass transition temperature, demonstrating the actuating ability with a relatively large region. In general, the CEF/SMP composite is promising for the application of morphing skins.

A new Cd(II) complex, [Cd(H4pbidc)(H2O)] n (1), incorporating 2,2′-(propane-1,3-diyl)bis(1H- imidazole-4,5-dicarboxylic acid) (H6pbidc) was synthesized and characterized by elemental analysis, infrared spectra and X-ray single-crystal diffraction. In complex 1, each Cd(II) ion is hepta-coordinated, showing a significantly distorted pentagonal-bipyramidal coordination environment. Adjacent Cd(II) ions are alternately joined through two carboxylate oxygen atoms and two bridging water molecules resulting in a one-dimensional chain structure. In the solid state, adjacent chains are further linked by hydrogen bonds, forming a three-dimensional supramolecular architecture. Meanwhile, the interactions of complex 1 with bovine serum albumin were analysed by fluorescence measurements under physiological conditions. The results indicated that the fluorescence intensity of bovine serum albumin was decreased considerably upon the addition of complex 1 through a static quenching mechanism with formation of one binding site. The negative values of the thermodynamic parameters including enthalpy change (Δ H), entropy change (Δ S) and Gibbs free energy change (Δ G) showed that hydrogen bonding and van der Waals forces were the main interactions in the binding of complex 1 to bovine serum albumin, and the binding process is spontaneous in thermodynamics.

We examine the impact of beauty on the academic career success of tenure-track accounting professors at top business schools in America and show that beauty plays a significant role. Specifically, after controlling for gender, ethnicity, publication history, work experience, and quality of alma mater, more attractive professors obtain better first school placements post-PhD and are granted tenure in a shorter period of time. These findings are broadly consistent with behavioral theory which predicts that facial attractiveness irrationally affects the perception of performance characteristics. Interestingly, there is no incremental benefit of attractiveness for the career progression from associate to full professor. This finding is consistent with the notion that the role played by beauty in promotion diminishes when the individual’s ability and competency become apparent over time.

Shape memory polymers have been studied as the matrix of lightweight self-deployable space structures for decades. The epoxy-based shape memory polymer, which is a potential material for aerospace application, has been tested about their resistance abilities to the ultraviolet radiation and vacuum thermal cycling by using ground-based simulation facilities. The wavelength of ultraviolet radiation is 250–400 nm with not less than five times the solar constant, and the irradiation times are 80, 160, and 240 h, respectively. The vacuum level, temperature range, and cycling times of vacuum thermal cycling are 10−5 Pa; −100°C to +100°C; and 0 cycle and 15, 30, and 45 cycles, respectively. The shape memory polymer specimens are compared for mass loss ratio, chemical compositions, surface morphology, and mechanical properties before and after the ultraviolet radiation and thermal cycling. The experimental results indicate that the glass transition temperature (Tg), mass loss ratio, modulus, and yield and break strength increase after experiencing 240h ultraviolet radiation or 45 thermal cycles, which shows great potential of epoxy-based shape memory polymer in aerospace structures and device applications.

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.

The objective of this paper is to investigate the flame structure and liftoff behaviors of a dimethyl ether central jet in CH4/air vitiated coflow in a coflow burner. The liftoff behaviors of dimethyl ether jet flames in the air flow were studied firstly. The flame stability of the burner was analyzed by measuring the flow field temperature with thermocouples. By changing the coflow rate and CH4 equivalence ratio, the liftoff behaviors of dimethyl ether jet flames under different vitiated coflow environments were discussed. The jet flame structure was also analyzed qualitatively by high-speed photography.

The coordination polymer {[Zn3(HhmIDC)2(H2O)2]·2H2]O} n [H4hmIDC = 2-(hydroxymethyl)-1 H-imidazole-4,5-dicarboxylic acid] has been synthesised and structurally characterised. In the polymer, there are two crystallographically distinct Zn(II) ions that adopt different coordination environments. The polymer exhibits good fluorescence properties in the solid state at room temperature and its thermogravimetric properties are also described.

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.

As a main component of space deployable structure, shape memory polymer composites are exposed to long-term periodic sharp temperature changes. It is necessary to investigate the influence of temperature on strength property of shape memory polymer composites. In this article, a micromechanical strength predication model was developed based on composite bridging model, which was used to define the stiffness matrix and relate the stress increment to the fiber and matrix. Furthermore, the progressive failure strength of shape memory polymer composites was simulated simply based on the properties of the material and the geometric parameters of the laminates. Comparison of the predictions with the experimental measurements was carried out. In general, the overall correlation between the theory and the experiments was reasonable. Furthermore, the model has been applied to predict the transverse strength, axial strength, and in-plane shear strength of different composite laminates (fiber content and ply angle) at different temperatures.

A traditional aircraft is optimized for only one or two flight conditions, not for the entire flight envelope. In contrast, the wings of a bird can be reshaped to provide optimal performance at all flight conditions. Any change in an aircraft’s configuration, in particular the wings, affects the aerodynamic performance, and optimal configurations can be obtained for each flight condition. Morphing technologies offer aerodynamic benefits for an aircraft over a wide range of flight conditions. The advantages of a morphing aircraft are based on an assumption that the additional weight of the morphing components is acceptable. Traditional mechanical and hydraulic systems are not considered good choices for morphing aircraft. “Smart” materials and structures have the advantages of high energy density, ease of control, variable stiffness, and the ability to tolerate large amounts of strain. These characteristics offer researchers and designers new possibilities for designing morphing aircraft. In this article, recent developments in the application of smart materials and structures to morphing aircraft are reviewed. Specifically, four categories of applications are discussed: actuators, sensors, controllers, and structures.

This article reviews the main progress in the development of typical thermoset shape memory polymers. Thermoset polymers are usually stronger in their microstructure than thermoplastic polymers due to their covalently crosslinked three-dimensional networks. The virtues of thermoset polymers make them great source materials for shape memory polymers. However, their three-dimensional networks endow thermoset shape memory polymers with not only high shape fixity rates and shape recovery rates but also low deformation abilities and brittleness. In the past decade, many breakthroughs have been made regarding thermoset shape memory polymers. Typical thermoset materials, such as epoxy resin, cyanate resin, thermoset polyurethane, polyimide, and polystyrene, have been studied as raw materials for shape memory polymers. Studies on thermoset shape memory polymers have been carried out to not only improve their fundamental properties (i.e. broadening of their operating temperatures and service environments and enhancing their thermal stabilities and mechanical properties) but also introduce functional performance properties (e.g. responsiveness to light, electricity, magnetism, and chemical stimuli). This article aims to present a brief review of the development of thermoset shape memory polymers, including the selection and preparation of materials, the improvement of properties, the functionalization of their composites, and their potential applications.

The work describes a concept to morph the thickness of airfoils using a combination of pneumatic flexible tubes within a Kirigami honeycomb configuration that represents the wingbox structure. The configuration of the honeycomb/inflatable tube structure is composed by a pair of flexible tubes sandwiched between two custom honeycomb layouts. At zero input pressure, the tube assumes a sinusoidal shape, which is reduced to a straight configuration and increase of the airfoil thickness when pressure is applied. An analytical model is developed for design purposes to consider the actuation authority and thickness change provided by the system proposed. The results are benchmarked against experimental tests carried out on a reduced-scale demonstrator.

As a kind of smart materials, shape memory polymer has covered broad applications for its shape memory effect. Precise description of the mechanical behaviors of shape memory polymer has been an urgent problem. Since the phase transition was a continuous time-dependent process, shape memory polymer was composed of several individual transition phases. Owing to the forming and dissolving of individual phases with the change in temperature, shape memory effect emerged. In this research, shape memory polymer was divided into different kinds of phases including frozen and active phases for its thermodynamics properties. Based on the viscoelasticity theory and phase transition theories, a new constitutive model for shape memory polymer which can explain the above assumptions was studied. In addition, a normal distribution model, which possesses less but physical meaning parameters, was proposed to describe the variation in the volume fraction in shape memory polymer during heating or cooling process.

An intelligent algorithm was developed based on backpropagation artificial neural network for the acoustic emission source localization. The established and trained methods of the algorithm were stated with the time difference of arrival detected by a fiber optic acoustic emission sensor array and the coordinates of acoustic emission source. The response characteristic of fiber optic acoustic emission sensor was calibrated with the commercial piezoelectric ceramic transducer (PZT) acoustic emission sensor, which provided that the fiber optic acoustic emission sensor was better suited to detect the low frequency of stress wave than the PZT sensor. Four fiber optic acoustic emission sensors were deployed in a square array in an aluminum plate for comparisons between different algorithms of source localization. Comparison results of acoustic emission source location provided that the intelligent algorithm improved the accuracy by reducing the nonlinear errors. For the anisotropic materials, a sensor array deployed in a diamond pattern was adopted. The velocities of stress waves in orthogonal directions were measured as the basic performance for both algorithms of source localization. Four sensors were integrated into a carbon fiber–reinforced polymer plate as a perfect structure for locating the acoustic emission source impacting on its surface. The experiment results provide that the maximum error is only 6.3 mm using the intelligent algorithm.

Advanced polymer matrix composite is a brittle material, and local fibre, matrix fracture and bonding delamination will cause the catastrophic failure of the composite. So, the strain and damage structural health monitoring of the composite material and its structures is very important for its applications. Based on the piezo-resistivity effect, micro-pore structure and resin infiltration properties of buckypaper, in this study, we develop a self-sensing composite based on embedded buckypaper, which only acts as a sensing layer to monitor the strain and damage of the composite. The strain and damage of the composite are reflected by the resistance change in the embedded buckypaper. The strain sensing properties of the buckypaper/epoxy film with different buckypaper aspect ratios 3:1, 6:1, 9:1, 12:1 and 15:1 were studied with voltammetry method, and the results indicated that there were two-stage relation between resistance change and strain, and under low strain level (~2000 µε), the strain sensitivity was nonlinear and unstable, but in the high strain level, the strain sensitivity was high with strain factor about 6.2, which was independent of the dimension of buckypaper layer. The self-sensing composite made of glass fibre–reinforced composite with embedded buckypaper shows the same strain sensing properties as buckypaper/epoxy film; at same time the damage revolution of the composite could be monitored by resistance development. The scanning electron microscope characterization demonstrated that the resin can penetrate into buckypaper of the composite and form strong bonding interface. The self-sensing composite can be applied in further large-scale advanced polymer composite materials and structures structural health monitoring (strain monitoring and damage detecting).

Shape memory polymers are temperature-controlled variable stiffness materials, which have potential for use as morphing skins. Shape memory polymer skins undergo large strain in their flexible, rubbery state and resist aerodynamic loads in their stiff, glassy state. However, pure shape memory polymers are brittle in their glassy state, and in their rubbery state, they tear rapidly along micro-cracks formed under tension. Due to these disadvantages, the shape memory polymers are not safe and reliable enough for application. In this article, elastic fibers were mixed into pure shape memory polymers to solve these problems. The mechanical properties of the shape memory polymer composites were investigated. The strength and Young’s modulus of pure shape memory polymers at high temperature were improved by elastic fibers, and the toughness of pure shape memory polymers at room temperature (glassy state) was enhanced with acceptable reduction in Young’s modulus. The tear strength of shape memory polymers was significantly improved by elastic fibers, especially at high temperature. Recovery properties and thermal performance were also discussed. Finally, shape memory polymer composite skins were used in a variable camber wing structure to demonstrate their application.

In this study, a kind of morphing skin composed of silicon rubber and shape memory polymer composite tube is designed, manufactured, and investigated. Significant stiffness variation for the morphing skin can be obtained through changing its environment temperature. First, in order to investigate the basic elastic properties of the morphing skin, the Rule of Mixture is used to predict the effective engineering modulus and modulus ratio with different matrix volume fractions. The tensile test is conducted on the skin in two states (cold state and heated state) to validate the accuracy of the theoretical method. Second, the temperature distribution of shape memory polymer composite tube heated by the hot fluid is obtained through the finite element analysis. Moreover, a corresponding heating system is designed and manufactured to provide heat for the morphing skin. Based on the heating system, the deflection and recovery performances are also investigated through the stress-bearing capability and thermal cycling tests, respectively. Finally, the infrared test is carried on the morphing skin to show the temperature distribution during the heating process.

This work presented an indirect method to monitor the deformation of the flexible variable camber wing using attached fiber Bragg gratings. To measure the transverse strains resulting from deformation of flexible variable camber wing, two groups of fiber Bragg grating sensors were attached on both upper and lower surfaces of the metal sheet, which was used to replace the traditional hinges. When the flexible variable camber wing was actuated by the lower surface’s pneumatic artificial muscle actuators, the upper surface would undergo the tensile deformation. A redshift could be observed from the reflective wavelength of the fiber Bragg grating sensors located on the upper surface. On the contrary, a blueshift could also be observed from the lower surface due to the compressive deformation. The comparison of the results with those obtained from strain gauges demonstrated the reliability of fiber Bragg grating sensors. Then, the vertical displacement and deflection angle of the flexible variable camber wing were obtained through the von Karman strain–displacement relation. A finite element model of the flexible variable camber wing was developed to simulate the variation of strain and displacement, which is caused by deformation of the metal sheet. A good agreement could be seen from the vertical displacements among the fiber Bragg grating strain sensors, finite element model, and direct measurements with laser range-finders.

In this article, the epoxy-based shape memory polymers were exposed to simulated γ-radiation environments up to 140 days for an accelerated irradiation. The influence of γ-radiation on thermal and mechanical properties was evaluated by differential scanning calorimetry, dynamic mechanical analysis, and tensile test. The glass transition temperatures ( Tg) determined by differential scanning calorimetry and dynamic mechanical analysis decreased no more than 10%, and the shape recovery speed became a little faster after γ-radiation of 1 × 105 Gy. The tensile strength and elastic modulus could, respectively, maintain 26 MPa and 1.36 GPa after being irradiated by 1 × 106 Gy radiation, showing great potential in aerospace structural materials.

This study investigated the mechanical and shape recovery properties of a styrene-based shape memory polymer composite reinforced by cup-stacked carbon nanotubes. Due to their unique morphology, cup-stacked carbon nanotubes could be well dispersed in the polymer matrix and offer remarkable benefits in the load transfer between the reinforcement fillers and shape memory polymer. Under the same amount of fillers, shape memory polymer composites embedded with cup-stacked carbon nanotubes exhibit superior mechanical properties in comparison with those embedded with multiwalled carbon nanotubes and carbon nanofibers. The elastic modulus, tensile strength, and flexural strength of the 2 wt% cup-stacked carbon nanotube–reinforced shape memory polymer composite increased by 61%, 66%, and 84%, respectively. It was also found that the glass transition temperature of shape memory polymer composite decreased from 61.9°C to 52.8°C by introducing 2 wt% cup-stacked carbon nanotubes, indicating that the shape recovery process could be triggered more easily by external stimulus due to the role of reinforcement fillers. Finally, under the external resistance load, the developed shape memory polymer composite was successfully driven to recover their shapes under thermal stimulus. The cup-stacked carbon nanotubes were proved to be a promising candidate for the polymer reinforcement.

This article demonstrates the use of embedded fibre Bragg gratings as vector bending sensor to monitor two-dimensional shape deformation of a shape memory polymer plate. The shape memory polymer plate was made by using thermal-responsive epoxy-based shape memory polymer materials, and the two fibre Bragg grating sensors were orthogonally embedded, one on the top and the other on the bottom layer of the plate, in order to measure the strain distribution in both longitudinal and transverse directions separately and also with temperature reference. When the shape memory polymer plate was bent at different angles, the Bragg wavelengths of the embedded fibre Bragg gratings showed a red-shift of 50 pm/° caused by the bent-induced tensile strain on the plate surface. The finite element method was used to analyse the stress distribution for the whole shape recovery process. The strain transfer rate between the shape memory polymer and optical fibre was also calculated from the finite element method and determined by experimental results, which was around 0.25. During the experiment, the embedded fibre Bragg gratings showed very high temperature sensitivity due to the high thermal expansion coefficient of the shape memory polymer, which was around 108.24 pm/°C below the glass transition temperature ( Tg) and 47.29 pm/°C above Tg. Therefore, the orthogonal arrangement of the two fibre Bragg grating sensors could provide a temperature compensation function, as one of the fibre Bragg gratings only measures the temperature while the other is subjected to the directional deformation.

The work describes the design, manufacturing, and parametric modeling of a curved cellular structure (SILICOMB) with zero Poisson’s ratio produced using Kirigami techniques from polyetheretherketone films. The large deformation behavior of the cellular structure is evaluated using full-scale finite element methods and experimental tests performed on the cellular samples. Good agreement is observed between the mechanical behavior predicted by the finite element modeling and the three-point bending compression tests. Finite element simulations have also been used to perform a parametric analysis of the stiffness against the geometry of the cellular structures, showing a high degree of tailoring that these cellular structures could offer in terms of minimum relative density and maximum stiffness. The experimental results also show high levels of strain-dependent loss factors and low residual deformations after cyclic large deformation loading.

The influence of cross-linking agent content on thermomechanical properties and shape recovery behavior of thermoset styrene shape memory polymer (SMP) was investigated in this article. The SMP was polymerized by free radical reaction, with styrene and butyl acrylate as comonomers and divinylbenzene as the cross-linking agent. When the cross-linking agent content is increased from 1 to 4 wt%, the storage modulus and the glass transition temperature ( Tg) of the SMP increased correspondingly. During the glass transition, while the value of damping peak decreased as a result of the addition of the cross-linking agent, the peak width increased, and the main relaxation activation energy increased by 48.6%. When the active temperature was higher than or equal to Tg, the SMP samples containing different weight percentages of the cross-linking agent could recover their original shape. At or above Tg, SMP with varied fractions of cross-linking agent could completely recover its original shape; the recovery rate of SMP increased with the increase in the contents of the cross-linking agent. Below Tg, SMP could not recover its original shape, but the recovery angle increased as the contents of cross-linking agent increased. These results were attributed to the increase of cross-linking densities as a result of the addition of cross-linking agent.