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In this work, a NiTi shape memory alloy (SMA) wire was embedded into a rubber/shape memory polymer (SMP) soft matrix to form a composite strip with a two-way reversible bending behavior. First, the elastic moduli of SMA wire were characterized as increasing about 3 times (18.6 GPa at martensite phase and 50.1 GPa at austenite phase) from 25 °C to 90 °C. Then, an SMA composite strip using SMP to replace the rubber matrix was fabricated to significantly improve the load-bearing ability (16-fold) at 28 °C. After that, the good two-way bending behaviors of the rubber/SMP-based SMA strip with high shape deploying ratio above 80% were demonstrated. Finally, the application of rubber/SMP-based composite strips in a space-deployable antenna model with two-way reversible bending behavior was developed and demonstrated through a heating and cooling temperature cycle.

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.

Linerless composite cryogenic tank is significant for weight reducing in launch vehicles, and a microscopic-to-macroscopic model is presented in this paper to capture the burst behaviors of the car...

The motivation of this work is to build a multimodal-based COVID-19 pandemic forecasting platform for a large-scale academic institution to minimize the impact of COVID-19 after resuming academic activities. The design of this multimodality work is steered by video, audio, and tweets. Before conducting COVID-19 prediction, we first trained diverse models including traditional machine learning models (e.g., Navie Bayes, SVM, and TF-IDF) and deep learning models (e.g., LSTM, MobileNetV2 and SSD) to extract meaningful information from video, audio, and tweets by i) detecting and counting face masks, ii) detecting and counting cough for potential infected cases, and iii) conducting sentiment analysis based on COVID-19 related tweets. Finally, we fed the multimodal analysis results together with daily confirmed cases data and social distancing metrics into the LSTM model to predict the daily increase rate of confirmed cases for the next seventh day. Finally, important observations with supporting evidence are presented.

As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a cross-twist/flat structure with a torsion angle of 60°, but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400–2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400–2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached −44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.

In recent years, two-dimensional (2D) halide perovskites have been widely used in solar cells and photoelectric devices due to their excellent photoelectric properties and high environmental stability. However, the terahertz (THz) and ultrafast responses of the 2D halide perovskites are seldom studied, limiting the developments and applications of tunable terahertz devices based on 2D perovskites. Here, 2D R-P type (PEA)2(MA)2Pb3I10 perovskite films are fabricated on quartz substrates by a one-step spin-coating process to study their THz and ultrafast characteristics. Based on our homemade ultrafast optical pump–THz probe (OPTP) system, the 2D perovskite film shows an intensity modulation depth of about 10% and an ultrafast relaxation time of about 3 ps at a pump power of 100 mW due to the quantum confinement effect. To further analyze the recombination mechanisms of the photogenerated carriers, a three-exponential function is used to fit the carrier decay processes, obtaining three different decay channels, originating from free carrier recombination, exciton recombination, and trap-assisted recombination, respectively. In addition, the photoconductor changes (∆σ) at different pump–probe delay times are also investigated using the Drude-Smith model, and a maximum difference of 600 S/m is obtained at τp = 0 ps for a pump power of 100 mW. Therefore, these results show that the 2D (PEA)2(MA)2Pb3I10 film has potential applications in high-performance tunable and ultrafast THz devices.

Effective electromagnetic interference (EMI) shielding requires materials with high permittivity. The current study reports 3D printed polymer-derived SiOC ceramics (PDC) modified with SiC nanowires (SiCnw) exhibiting both high real and imaginary parts of permittivity within X-band. SEM results indicated that a large number of pores and cracks exist in the SiOC, and twinned SiCnw were uniformly grown among them along with the existence of graphite microcrystals when the sintering temperature was 1500 ℃. The real part of permittivity ranged from 16.6 to 28.9 while the imaginary part from 31.7 to 34.2 in X-band. The EMI total shielding effectiveness (SET) of the ceramics could reach 34.7 dB with absorption loss (SEA) of 29.3 dB and reflection loss (SER) of 5.4 dB. Meanwhile, the 3D printed PDC-SiOC ceramics at 900 ℃ sintering temperature possess certain mechanical properties with the magnitude of compressive strength being 12.57 MPa.

The numerical method for predicting the permeability of a laminated composite based on matrix cracks is improved to meet the application at a cryogenic temperature. The number of the parameters tha...

The proliferation of edge computing technologies has boosted the development of new applications for a plethora of edge devices. However, many applications face privacy issues and bandwidth limitations. To solve these limitations, we propose a collaborative learning framework on the edges, named CLONE, which is steered by the real-world data sets collected from a large electric vehicle (EV) company and a grocery store of a shopping mall, respectively. We categorize two application scenarios for CLONE, i.e., CLONE in the training stage (CLONE_ training ) and CLONE in the inference stage (CLONE_ inference ). As to CLONE_ training , we choose the failure prediction of EV battery and associated components as the first use case. While as for CLONE_ inference , customer tracking in a grocery store is selected as another case study. In this work, the goal of the CLONE is to support real-time training and inference for connected vehicles and marketing intelligence services. Our experimental results on the EV data show that CLONE is able to reduce model training time without sacrificing algorithm performance. Furthermore, the experimental results on the video data from the grocery store reveal that CLONE is a useful approach to solve the multitarget multicamera tracking problem in a collaborative fashion.

The recent proliferation of computing technologies (e.g., sensors, computer vision, machine learning, and hardware acceleration) and the broad deployment of communication mechanisms (e.g., dedicated short-range communication, cellular vehicle-to-everything, 5G) have pushed the horizon of autonomous driving, which automates the decision and control of vehicles by leveraging the perception results based on multiple sensors. The key to the success of these autonomous systems is making a reliable decision in real-time fashion. However, accidents and fatalities caused by early deployed autonomous vehicles arise from time to time. The real traffic environment is too complicated for current autonomous driving computing systems to understand and handle. In this article, we present state-of-the-art computing systems for autonomous driving, including seven performance metrics and nine key technologies, followed by 12 challenges to realize autonomous driving. We hope this article will gain attention from both the computing and automotive communities and inspire more research in this direction.

Three types of representative unit cell (RUC) of [±θ/904]S composite laminates and cracked plies were created to obtain the constitutive model of the cracked plies and to compare their accuracy of ...

As a novel and attractive advanced manufacturing technology, three-dimensional (3D) printing can realize the manufacturing of devices with more sophisticated structures. Metamaterials (MMs) are a novel material design idea based on the variation of physical structural designs, in order to break through apparent and intrinsic natural laws of matter, and eventually obtain extraordinary material functions. With the development of stealth technology, it has become a hot topic to seek and design radar absorbing materials to realize the high-performance requirements of “thin, light weight, wide and strong”. At this time, 3D-printed MMs with various sophisticated structures exhibit great application potential. Recent studies report the development of a wide variety of 3D-printed electromagnetic MMs (EMMs), which are attracting increasing scientific attention. To better advance the design of 3D-printed MMs, it is necessary to fully comprehend the advantages and disadvantages of various printing technologies, and fully understand the latest progress in printed EMMs. Four-dimensional (4D) printing is a combination of 3D printing and smart materials, which unfolds new opportunities for intelligent and customized development in aerospace and electronic devices. The present work reviews the research progress in electrical MMs printed using various 3D/4D printers. Emphasis is placed on the structural design of EMMs, selection of absorbing bases, category of absorbing materials, 3D printing types and EM absorption performance. As the demand for data grows rapidly, 5G wireless mode is developed. Technology from 100 GHz to 1.0 THz frequency bands has great potential in wireless communications for the upcoming 6G. 3D-printed electronic antennas and 5G/6G antennas fabricated by other processes are also briefly summarized. Meanwhile, the article discusses and looks forward to the potential future design and development of 3D/4D printed electrical AMMs for stealth and antenna applications.

As a new type of molding technology, three dimensional (3D) printing can realize the manufacturing of devices with complex shapes. In the current study, 3D printed polymer-derived ceramics (PDCs), whose molecules are customizable and designable, were fabricated to achieve high-intensity broadband absorption performance of electromagnetic (EM) wave radiation. Based on improving the surface impedance matching characteristics, with the aim of optimizing the attenuation characteristics, cross convex/flat bilayer structures and cross concave/flat bilayer structures were fabricated, respectively. Remarkably, the former exhibited a minimum reflection coefficient (RCmin) of −58.97 dB at a thickness of 3 mm, and a broadband absorption of 4.0 GHz in X-band (8.2–12.4 GHz) at 3.4 mm. More significantly, we successfully combine the cross-convex structure with the cross-concave structure of PDCs–SiOC in the same as well as in different layers to obtain parallel and series structures respectively. It was found that the EM absorption performance of parallel structures was better than that of series structures, which is attributed to the stronger resonance between the parallel structures than between the series structures. The generation of dipole and interfacial polarization of PDCs–SiOC and the advancement of conductivity contribute to the increase of dielectric loss. Consequently, the PDCs–SiOC with multifarious structures are promising radar stealth absorbing materials in aerospace field.

This paper design two kinds of damping interleaves, traditional thermoplastic polyurethane (TPU) and novel carbon nanotube (CNT) modified TPU porous membranes are designed and respectively interleaved into the interfaces of a carbon fiber-reinforced plastic (CFRP). How the interleaves affect the damping behaviors and quasi-static mechanical properties of the CFRP is comparatively investigated. Results show that both TPU and CNT/TPU interleaved CFRPs possess good damping behaviors within a wide temperature range of 50∼150°C as well as a wide frequency band from 0.1 to 30 Hz, where, the former is a little better. But, storage modulus of the CNT/TPU interleaved CFRP is always higher than that of the TPU interleaved CFRP at different temperatures and frequencies. Moreover, the flexural strength and interlaminar shear strength are both decreased by 36.0% and 24.0% for the TPU interleaved CFRP, and 20.0% and 17.8% for the CNT/TPU interleaved CFRP, respectively, when compared to the baseline CFRP, suggesting the CNT/TPU interleaf brings less negative effect on the mechanical properties of CFRP. Comparatively, CNT/TPU interleaved CFRP is more multifunctional, possessing good damping feature and reasonable mechanical properties, which is maybe more potential in the structural-functional field, especially where needs shock absorption and noise reduction.

The porous carbon/Fe3O4 composites have been used to adsorb the dyes recently, however, most carbon sources are not preferable for the environment protection. In this paper, the porous carbon/Fe3O4 composites were synthesized by a simple step carbonization method using the waste cigarette butts and the ferric nitrate as carbon source and oxidizer, respectively. Notably, the obtained products can be reused. The results show that the crystallite size of as-prepared Fe3O4 will increase at high treating temperature. In addition, the sample of C-Fe3O4-1000 possesses the highest saturation magnetization of 92.2 emu g−1, and the sample of C-Fe3O4-600 has the highest specific surface area of 90.23 m2 g−1 and the maximum adsorption of 102.04 mg g−1 for methyl orange. Furthermore, the adsorbent can maintain an excellent adsorption capacity for the dye after 4 cycles. Therefore, as-prepared porous carbon/Fe3O4 composite is an excellent candidate for recyclable dye adsorbent, and the waste can be converted into products for reducing the environment pollution.

Purpose The purpose of this paper is to developing a kind of acoustic metamaterial with wide frequency band especially in low frequency region. At the same time, its the tunability of sound insulation frequency is achieved. Design/methodology/approach A three-dimensional (3D) acoustic metamaterial consisting of rigid frame, spherical attachment and thin film is proposed. The material parameters and the effect of the attachment hole on the forbidden band are investigated by finite element simulation. The sound insulation effect of the structure is validated by the combination of simulation and experiment. Findings The results show that the elastic modulus of the structural material determines the initial frequency of the forbidden band of the proposed 3D acoustic metamaterials. The lower the elastic modulus of the structural material, the lower the initial frequency of the forbidden band. The material parameters of the frame mainly affect the initial frequency of the first forbidden band, and the material parameters of the attachment will affect both the initial and termination frequency of the first forbidden band. Holes in the attachments reduce the band gap width. The characteristic curve moves down with the increase of subtracted mass. Research limitations/implications The findings may greatly benefit the application of the acoustic metamaterials in the fields of sound insulation and noise reduction. Originality/value This acoustic metamaterial structure has excellent sound insulation performance. At the same time, the single cell structure can be assembled into any shape. The structure can achieve sound selective filtering and combination control.

The tribological properties of hybrid polytetrafluoroethylene (PTFE)/aramid fibers 1414 (Kevlar) fabric self-lubricating composite under different conditions was studied. To improve tribological properties and the bonding performance of PTFE, the hybrid Kevlar/PTFE fabrics were treated by sodium-naphthalene complex liquid. PTFE/Kevlar fabric composite was prepared by phenolic-epoxy (6:4) resin. Tribological properties of the composite, friction coefficient and wear amount, were analyzed using varying loads and speeds on a friction and wear testing machine. Worn surface morphology and transfer film were observed by Scanning electron microscopy (SEM). The results showed that the coefficient of friction decreased with the decrease of load and the increase of rotating speed. In addition, the composites with higher PTFE content showed better lubricating behavior. The friction coefficient of the composites reinforced by modified fabrics were more stable and the PTFE transfer film remains more complete.

Mesoporous carbon/graphene composites (MCG) have exhibited good electrochemical performances; however, the fixed mesoporous carbon, the low specific surface area, and porosity are the main obstacles in their application in supercapacitors. In this paper, mesoporous carbon microspheres/graphene composites (MCMG) were synthesized in situ via a soft template method and subsequent thermal reduction by using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent, and aqueous mesophase pitch (AMP) and graphene oxide (GO) as the carbon sources. The strong electrostatic interaction between GO/CTAB and AMP promoted the self-assembly of CTAB and AMP to form the MCMG precursor. The results showed that the CTAB concentration and aging temperature have an important effect on the morphology and pore structure of the synthesized MCMG. The high aging temperature promoted the formation of mesoporous carbon spheres and its diameter increased with the increase in the concentration of CTAB. The as-prepared MCMG at the aging temperature of 140 °C had obvious spherical and layered carbon materials after carbonization at 900 °C. When the concentration of CTAB was 10.6 g L−1, the formed mesoporous carbon spheres with the diameter of 30–40 nm were uniformly dispersed among the layered graphenes in MCMG-140-0.2 (the aging temperature of 140 °C and the CTAB content of 0.2 g). In addition, its specific surface area was 1150.5 m2 g−1 and the mesopore size was centered at 4.3 nm, 7.9 nm, and 17.1 nm. Compared with the MCMG precursor, the ordered degree of the mesopores for MCMG was reduced due to the high temperature carbonization. Importantly, the specific capacitance of MCMG-140-0.2 at the current density of 0.1 A g−1 was as high as 356.3 F g−1. Moreover, the specific capacitance of MCMG-140-0.2 at 1 A g−1 remained at 278.5 F g−1, the capacitance retention was 92.1% after 6000 cycles, and the coulombic efficiency was over 98% at a high current density of 2 A g−1. Therefore, the as-prepared MCMG can be an excellent candidate for electrode materials in supercapacitors.

Highlights Ultrathin, lightweight, and flexible carbon nanotube buckypaper enhanced using MXenes (Ti3C2Tx) for high-performance electromagnetic interference shielding is synthesized through facile electrophoretic deposition.The obtained Ti3C2Tx@CNT hybrid buckypaper demonstrates outstanding EMI shielding effectiveness of 60.5 dB in the X-band at 100 μm and a specific SE value of 5.7 × 104 dB cm2 g−1 at 5 μm. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00597-4., Lightweight, flexibility, and low thickness are urgent requirements for next-generation high-performance electromagnetic interference (EMI) shielding materials for catering to the demand for smart and wearable electronic devices. Although several efforts have focused on constructing porous and flexible conductive films or aerogels, few studies have achieved a balance in terms of density, thickness, flexibility, and EMI shielding effectiveness (SE). Herein, an ultrathin, lightweight, and flexible carbon nanotube (CNT) buckypaper enhanced using MXenes (Ti3C2Tx) for high-performance EMI shielding is synthesized through a facile electrophoretic deposition process. The obtained Ti3C2Tx@CNT hybrid buckypaper exhibits an outstanding EMI SE of 60.5 dB in the X-band at 100 μm. The hybrid buckypaper with an MXene content of 49.4 wt% exhibits an EMI SE of 50.4 dB in the X-band with a thickness of only 15 μm, which is 105% higher than that of pristine CNT buckypaper. Furthermore, an average specific SE value of 5.7 × 104 dB cm2 g−1 is exhibited in the 5-μm hybrid buckypaper. Thus, this assembly process proves promising for the construction of ultrathin, flexible, and high-performance EMI shielding films for application in electronic devices and wireless communications. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00597-4.

The great success of artificial intelligence and edge computing technology has largely promote the development of connected and autonomous driving. However, owing to the missing of the experiment platform for Road-Side Unit (RSU), majority of research works are either simulation based task offloading or commercial equipment's based scheduling design. The fundamental challenge of how to co-design the communication and computation in a practical system is not tackled.In this paper, we proposed Equinox, which is our design of the rode-side edge computing experimental platform for connected and autonomous vehicles. With communication, data, as well as the computation taken into consideration, Equinox provides stable and sufficient communication based on a combination of WiFi, LTE, and DSRC. Also, Equinox guarantees reliable and flexible data collection, data storage, and efficient data processing.

Recent utilization of metamaterial design idea, which presents unique and designable electromagnetic properties, has been prompting the establishment of new stage of electromagnetic metamaterial absorber (EMMA) researches as well as enabling the possibility of the integration of structure and function. Great advances have been made since the first metamaterial perfect absorber (MPA) demonstrated in 2008. In addition to MPAs, broadband EMMAs, polarization independent and angle insensitive EMMAs and tunable EMMAs have been proposed to enlarge the application range of metamaterials in various situations. With an increasing demand for EMMAs operating at modern complex electromagnetic environment, the trend of high integration of full-band, wide-angle and active frequency tunable is inevitable in the future. From this perspective, a progress report should be given to summarize the progress in stages and to inspire researchers for their future studies. The emphasis of this report is given on the structural designs, absorbing performances, fabrication methods and the mechanisms of EMMA. Outlook and insight on the defect of current studies and future developing trend are also provided.

The interphase of composites is a vital element in controlling the overall performance. Herein, the SiC nanowires (SiCnw) were grown on the interface of the SiC fiber (SiCf)/Si3N4 composites and successfully achieved the integration of enhanced mechanical and electromagnetic wave (EMW) absorption performance. The introduction of SiCnw made the bonding between the SiCf and Si3N4 matrix more appropriate, thereby enhancing the mechanical properties. The defects, stacking faults, twin boundaries and heterogeneous interfaces in SiCnw improved the dielectric loss of the composites, which was beneficial to the consumption of EMW energy. Notably, the SiCf/SiCnw/Si3N4 composite containing 1.8 vol.% SiCnw demonstrated the optimal mechanical and EMW absorption properties, reaching a flexural strength of 333±29 MPa, a minimum reflection coefficient (RCmin) value of -51.4 dB with a thickness of 3.2 mm and an effective absorption bandwidth (EAB) of 3.5 GHz with a thickness of 2.8 mm. Besides, the fracture mechanism and EMW absorption mechanism are also discussed. This work provides a potential new way to prepare lightweight, stable, and high-performance EMW absorbing materials for aviation and aerospace.

Shape memory materials draw much attention due to various promising potential applications. This work prepares a novel shape memory composite via grading photo-thermal curing method, which has not yet been reported. Expectedly, it merges advantages of epoxy-based shape memory polymer (EP) and polyvinyl alcohol-based shape memory polymer (PVA), which has applicable stiffness and multi-stimuli responsive performance. The unsatisfactory mechanical properties of most water-driven shape memory polymer (SMP) is expected to be solved by this fabrication strategy, so that the application range of water-driven SMP could be further extended. The synergistic plasticization of PVA and EP dominates water-driven shape memory behavior of this composite. Interestingly, its water-driven shape memory performance is able to be further improved by immersed in HCl/EtOH solution. The glassy-to-rubbery modulus ratio (E′g/E′r) of the PVA/EP-HCl/EtOH is about 650 after immersed in 0.1 mol/L HCl/EtOH for 6 h. In addition, this immersed method also can solve the post curing problem of such cationic photocuring. It is an easy, efficient, economical strategy for improving synergistic water-driven shape memory performance. Furthermore, this shape memory composite is expected to provide new perspective and practical approach to realize the intellectualization of underwater deployment and release structure.

Shape memory polymer foam (SMPF) is being studied extensively as potential aerospace materials as they have high compression ratio, high specific strength and high specific modulus compared to other shape memory polymers. In this paper, a composite foam with shape memory epoxy as matrix and polyurethane as functional phase was prepared. The SMPF has been characterized by different analytical and testing methods, and its chemical crosslinking reaction and material properties have been studied. The SMPF was installed in the shape memory polymer composite (SMPC) flexible solar array system (SMPC-FSAS), and ground environment tests and orbital validation were performed. Considering the particularity of space environment, the thermal performance test of ground space environment can effectively test the reliability of shape memory performance. Finally, the SMPC-FSAS carried on SJ-20 satellite successfully deployed on geosynchronous orbit for the first time in the world. Moving forward, SMPF assesses the feasibility of applications in the space field and provides more valuable information.

In this study, the compressive properties and failure mode of reinforced composite skin structures having different delamination deficiencies were investigated systematically. Different kinds of delamination deficiencies were presented at specific locations in the specimens. The compressive mechanical properties of the materials were performed by axial compression testing, and strain distribution in different parts of the specimen and bearing capacity were monitored during the compressing processes. The ultimate compression bearing capacity, the failure mode and the expansion of internal damage were investigated as well. Results showed that the existence of delamination deficiencies have effects on the ultimate loading capacity of the specimens in different degree, in which the influence of delamination deficiencies in the skin is the most serious. Comparing with the specimen without deficiencies, the ultimate load-carrying capacity of the specimen with delamination deficiencies in the skin and in the stiffener under compressive load reduced by 38.58% and 22.34%, respectively. The failure modes of specimens with and without delamination deficiencies are similar. Compression failure is the main form of fracture for the stiffener, and the skin having different degree of buckling and delamination.

Shape memory polymers, as a kind of smart materials, play an important role in more and more fields, such as aerospace, biomedicine and intelligent clothing field and so on. Comparing with traditional materials, negative Poisson's ratio foam has excellent mechanical properties, such as double curvature, light weight, high shear resistance, auxetic etc., and it has a great potential application in the field of aerospace. Therefore, in this project, shape memory composite foam was fabricated based on the commercial soft polyurethane foam material as matrix and shape memory epoxy resin as functional phase. Negative Poisson's ratio of foam was fabricated based on its shape memory feature through a process of triaxial compression with heat treatment. Microstructure deformation was characterized after the transformation of auxetic foam. By adjusting the processing parameters, the auxetic shape memory foam with different “re-entrant” structure was obtained. Such fabricated shape memory composite foams display variable stiffness with auxetic behavior. Effective compressive and tensile modulus was obtained by compression and tension tests. The effect of processing parameters on foam Poisson's ratio was analyzed, which provided certain guiding significance for the further shape memory foam preparation.

This paper presents a multistable variable cross-section laminate (MVCL), which is designed by applying the displacement constraint at the two opposing ends of the laminate. A theoretical model describing the MVCL as rigid bars connected with compliant hinges is built to predict the equilibrium configurations and snap-through loads of the MVCL. The snap-through process of the multistable structure is investigated via experiment and finite element analysis (FEA). Subsequently, the theoretical model is improved by simplifying the middle segment of the MVCL as an elastic beam. Good agreement is obtained between the experimental test, FEA, and improved theoretical model results. It is shown that the current approach can be successfully applied to predict the equilibrium configurations and snap-through loads of an MVCL. The snap-through loads can be adjusted by changing the middle segment length of an MVCL. Keywords: Multistable structure, Variable cross-section, Composite laminate, Snap-through

Shape memory polymers (SMPs) are a kinds of smart materials that have capability of memorizing and recovering to their original shape in response to external stimuli. Comparing with the block SMPs, electrospun SMP mats with porosity and low mechanical property are better suited for a certain application, especially in bio-medical filed, tissue engineering, drug delivery, catalysis, etc. In this study, nanofiller enhanced composite membrane were developed based on Fe nanowire and (ethylene-vinyl acetate copolymer) EVA. Electrospinning technique was selected to fabricate this composite SMP membrane. To optimize shape memory effect, the cross-linked network was achieved by varying the UV curing time and cross-linking agent content. Remotely actuation composite membrane was completed by a light-thermal stimuli, which was assisted by Fe nanowire via light energy converting to thermal energy. High shape recovery rate was obtained via hot water actuation.

As we known, composite sandwich structure with advantages of high specific strength/modulus, high temperature resistance, damping, etc., which is widely used in various fields. And there is more space in its core to supply for multi-functional filler, which provides the possibility for special engineering applications (such as heat insulation, wave absorption, etc.). In this paper, a new type of lightweight composite lattice structure (called X-type lattice structure) is proposed based on the stretching dominated idea of quadrilateral grid and lattice strut. The mechanical properties and failure behavior of X-type lattice structures are investigated based on theoretical and experimental methods. The experiment results show that the mechanical properties of the X-type lattice sandwich structure is more superior than those of other pyramidal lattice sandwich structures. In theoretical analysis, we found the fact that the shear equivalent stiffness of X-type lattice structure is independent of the loading direction, while the shear strength is related to the loading direction. Meanwhile, its minimum shear strength will be reached at the 0 degrees loading direction, and the maximum shear strength will be obtained when the loading direction is 45 degrees.

Purpose This paper aims to exploit shape-memory polymers as self-healable materials. The underlying mechanism involved the thermal transitions as well as the enrichment of the healing reagents and the closure of the crack surfaces due to shape recovery. The multi-stimuli-triggered shape memory composite was capable of self-healing under not only direct thermal but also electrical stimulations. Design/methodology/approach The shape memory epoxy polymer composites comprising the AgNWs and poly (ε-caprolactone) were fabricated by dry transfer process. The morphologies of the composites were investigated by the optical microscope and scanning electron microscopy (SEM). The electrical conduction and the Joule heating effect were measured. Furthermore, the healing efficiency under the different stimuli was calculated, whose dependence on the compositions was also discussed. Findings The AgNWs network maintained most of the pathways for the electrons transportation after the dry transfer process, leading to a superior conduction and flexibility. Consequently, the composites could trigger the healing within several minutes, as applied with relatively low voltages. It was found that the composites having more the AgNWs content had better electrically triggered performance, while 50 per cent poly (ε-caprolactone) content endowed the materials with max healing efficiency under thermal or electrical stimuli. Research limitations/implications The findings may greatly benefit the application of the intelligent polymers in the fields of the multifunctional flexible electronics. Originality/value Most studies have by far emphasized on the direct thermal triggered cases. Herein, a novel, flexible and conductive shape memory-based composite, which was capable of self-healing under the thermal or electrical stimulations, has been proposed.

Purpose The purpose of this paper is to provide a review of recent systematic and comprehensive advancement in electrospun polymer fiber and their composites with shape memory property. Design/methodology/approach The nanofiber manufacture technique is initially reviewed. Then, the influence of electrospinning parameters and actuation method has been discussed. Finally, the study concludes with a brief review of recent development in potential applications. Findings Shape memory polymer (SMP) nanofibers are a type of smart materials which can change shape under external stimuli (e.g. temperature, electricity, magnetism, solvent). In general, such SMP nanofibers could be easily fabricated by mature electrospinning technique. The nanofiber morphology is mainly affected by the electrospinning parameters, including applied voltage, tip-to-collector distance, viscosity of solution, humidity and molecular weight. For actuation method, most SMP nanofibers and their composites can change their shapes in response to heat, magnetic field or solvent, while few can be driven by electricity. Compared with the block SMPs, electrospun SMP nanofibers’ mat with porosity and low mechanical property have a wide potential application field including tissue engineering, drug delivery, filtration, catalysis. Originality/value This paper provides a detailed review of shape memory nanofibers: fabrication, actuation and potential application, in the near future.

This paper introduces a new thermal control device (TCD) which has not only low weight and high efficiency but also passive and active cooling capabilities. The TCD mainly consists of hollow graphene-enhanced-metallic microlattice material, phase change material (PCM) and a peristatic pump. The PCM is inside the spatial-interconnected millimeter-scale diameter tubes, which are the basic constitution of the hollow microlattice material, in addition, the peristatic pump was connected with the tubes and used to force the liquid-state PCM to circulate inside the interconnected thin tubes. Thus, the proposed TCD takes combined advantages of the ultralight and high thermal transfer properties of the hollow graphene-enhanced-metallic microlattice materials, the thermal storage capability of the PCM and forced convection of the PCM driven by the peristatic pump as the PCM is in liquid state. The manufacturing process of the active TCD was also developed and proposed, which mainly includes additive manufacturing, composite electroless plating, polymer etching, liquid PCM injecting and the peristatic pump connecting. In addition to that, a thermal test system was built and the effective thermal conductivities of the TCD in passive cooling and with active cooling modes were experimentally studied. The TCD can absorb heat and actively dissipate heat by means of forced convection. Consequently, the proposed active TCD can be used to guarantee the electronic components and spacecrafts operate in a specific temperature range.

Matrix microcracking of laminated composites lead to stiffness degradation. Microscopic critical stresses are defined according to the linear elastic fracture mechanics and are found to be independent of the crack density. The microscopic critical stresses are constant as long as the material and the thickness of the cracked plies are constant, and can be used to obtain the semi-analytical expression of the equivalent transverse moduli and in-plane shear moduli of the cracked plies versus the crack density. The equivalent longitudinal moduli and in-plane shear moduli of [0/±θ4/01/2]S laminates are obtained by using the semi-analytical model and the classical laminate theory, and are compared with the available experimental data and conventional finite element analysis (FEA) results.

The COVID-19 pandemic brought unprecedented levels of disruption to the local and regional transportation networks throughout the United States, especially the Motor City---Detroit. That was mainly a result of swift restrictive measures such as statewide quarantine and lock-down orders to confine the spread of the virus and the rising number of COVID-19 confirmed cases and deaths. This work is driven by analyzing five types of real-world data sets from Detroit related to traffic volume, daily cases, weather, social distancing index, and crashes from January 2019 to June 2020. The primary goals of this work are: i) figuring out the impacts of COVID-19 on the transportation network usage (traffic volume) and safety (crashes) for the City of Detroit, ii) determining whether each type of data (e.g. traffic volume data) could be a useful factor in the confirmed-cases prediction, and iii) providing an early future prediction method for COVID-19 rates, which can be a vital contributor to life-saving advanced preventative and preparatory responses. In addressing these problems, the prediction results of six feature groups are presented and analyzed to quantify the prediction effectiveness of each type of data. Then, a deep learning model was developed using long short-term memory networks to predict the number of confirmed cases within the next week. The model demonstrated a promising prediction result with a coefficient of determination ( R 2 ) of up to approximately 0.91. Furthermore, six essential observations with supporting evidence are presented, which will be helpful for decision-makers to take specific measures that aid in preventing the spread of COVID-19 and protecting public health and safety. The proposed approaches could be applied, customized, adjusted, and replicated for analysis of the impact of COVID-19 on a transportation network and prediction of the anticipated COVID-19 cases using a similar data set obtained for other large cities in the USA or from around the world.

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.

In order to understand the formation of one-dimension periodic structures by electrospinning, an approximate mechanical approach for the critical load and the number of half waves in the buckled shape have been conducted based on the energy method. Diameter of circular cross-section electrospun fiber is assumed to be equal to the length of the rectangular cross-section spitted fiber. Fiber with rectangular cross section buckles more easily than that with circular cross section because of the different flexural rigidity. For rectangular-section fiber, increase of length to width ratio can result in the increase of the number of half waves. Detailed simulation results for buckling responses of circular-section fiber and rectangular-section fiber have been conducted by commercial finite element analysis software (ABAQUS).

Purpose The purpose of this paper is to develop an effective approach to significantly improve the thermomechanical properties of shape memory polymer (SMP) nanocomposites that show fast thermally responsive shape recovery. Design/methodology/approach Hexagonal boron nitrides (h-BNs) were incorporated into polymer matrix in an attempt to improve the thermal conductivity and thermally responsive shape recovery behaviour of SMP, respectively. Thermally actuated shape recovery behaviour was recorded and monitored instrumentally. Findings The results show that both glass transition temperature (Tg) and thermomechanical properties of the SMP nanocomposites have been progressively improved with increasing concentration of h-BNs. Analytical results also suggest that the fast-responsive recovery behaviour of the SMP nanocomposite incorporated with h-BNs was due to the increased thermal conductivity. Research limitations/implications A simple way for fabricating SMP nanocomposites with enhanced thermally responsive shape recovery based on the incorporation of h-BNs was developed. Originality/value The outcome of this study may help fabrication of SMP nanocomposites with fast responsive recovery behaviour.