Showing papers in "Composites Part B-engineering in 2021"

New development of ultra-high-performance concrete (UHPC)

Abstract: Ultra-high-performance concrete (UHPC) is a type of cement-based composite for new construction and/or restoration of existing structures to extend service life. UHPC features superior workability, mechanical properties, and durability compared with conventional concrete. However, some challenges limit the wider application of UHPC, such as low workability for large-volume production, high autogenous shrinkage, insufficient flexural/tensile properties, and unpredictable durability after concrete cracking. Therefore, this paper reviews the state-of-the-art technologies for developing UHPC mixtures with improved properties. This review covers the following aspects: (1) the existing design methodologies; (2) the typical ingredients (e.g., binders, aggregates, chemical admixtures, and fibers) for preparation of UHPC and the underlying working principals; (3) the technologies for improving and controlling key properties (e.g., workability, autogenous shrinkage, compressive performance, tensile/flexural properties, and durability); and (4) the representative successful applications. This review is expected to advance the fundamental knowledge of UHPC and promote further research and applications of UHPC.

A review of three-dimensional graphene-based aerogels: Synthesis, structure and application for microwave absorption

Abstract: Graphene aerogels (GAs) offer a distinctive combination of high porosity, low density, large specific surface area and high compressibility, which make it grab considerable attention in various applications, in particular for high performance electromagnetic wave attenuation. The internal porous structure and three-dimensional (3D) network of GAs solve the phenomenon of graphene sheet layer agglomeration, high conductivity and impedance mismatch in two-dimensional graphene, which is conducive to the improvement of microwave absorption performance. In addition, GAs incorporate other lossy materials as a framework have been widely studied to achieve more efficient microwave absorption. Herein, the latest advances in the synthetic strategies and structural characteristics of graphene-based materials are reviewed. Furthermore, we summarized recent advances in graphene-based aerogels as microwave absorbing materials, including pure GAs and hybrid aerogels with other lossy materials. In addition, we also highlighted the multifunctional microwave absorbing materials. On this basis, we summarized the research status of graphene-based microwave absorbing aerogels and put forward the challenges and outlook of graphene-based microwave absorbing aerogels.

A highly fire-safe and smoke-suppressive single-component epoxy resin with switchable curing temperature and rapid curing rate

Abstract: The design of highly fire-safe and smoke-suppressive single-component epoxy (EP) resins combining modest curing temperature and fast curing rate has been desirable yet very challenging in both academia and industry. Herein, we report a facile design of a phosphorus/imidazole-containing single-component EP system via incorporating 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and a flame-retardant curing agent cyclotriphosphazene-modified benzimidazole (BICP) into EP. Our results show that EP/DOPO/BICP exhibits a rapid modest-temperature curing feature because DOPO serves as a switch that triggers BICP to release benzimidazole (BIM) via substitution reaction in the initial curing stage. Moreover, as-prepared EP/DOPO/BICP shows outstanding fire retardancy, reflected by the high limited oxygen index (LOI) of 38.3% and UL-94 V-0 rating. Compared to the control EP system, the peak of heat release rate (PHRR) and total smoke production (TSP) of EP/DOPO/BICP remarkably decrease by ~74.5% and ~50.6%, respectively, which is superior to previously-reported flame-retardant P-containing epoxy counterparts. The significant enhancements in flame retardancy and smoke suppression are mainly due to the formation of a highly intumescent char layer and the reduced burning degree of pyrolysis fragments. This work offers a facile and scalable strategy for creating fast-curing, modest-temperature curable, highly fire-resistant and smoke-suppressive one-component epoxy systems applicable to large-scale industrial production.

Biomass derived porous carbon (BPC) and their composites as lightweight and efficient microwave absorption materials

Abstract: With the pursuit of high-efficiency microwave absorbing materials (MAMs), biomass derived porous carbon (BPC)-based materials have attracted a great deal of attentions due to their plentiful resources, low density and highly environment-friendly. The microwave absorption of BPC composites is closely correlated to their composition, surface chemical activity, microstructures, and pore size, which are in turn decisively determined by the biomass precursors and subsequent carbonization or activation. In this article, we provide a timely and comprehensive review on recent achievements for the microwave absorption properties of various BPC-based MAMs. Firstly, the general synthesizing approaches for carbon materials from various biomass sources, especially in relation to the carbonization and activation are summarized. Then, based on the basic microwave absorption theory, the performances of pure BPC served as microwave absorber are presented. After that, the strategies to improve the microwave absorption properties of BPC including heteroatom doping and the formation of composites with magnetic metals, metal oxides, polymers, and so on, are discussed as well. Finally, we provide discussions and prospects for the development of BPC as lightweight and efficient MAMs in the further. It is believed that the current progress in experimental investigations combined with theoretical predictions will greatly promote the design and development of lightweight and efficient MAMs. Moreover, as an important type of MAMs, views on the challenges and prospects of BPC-based MAMs are proposed as well.

Morphology-control synthesis of polyaniline decorative porous carbon with remarkable electromagnetic wave absorption capabilities

Abstract: Porous carbon materials have been widely reported on dealing with the electromagnetic (EM) wave interference. However, monotonous EM loss mechanism still performed an obstacle to achieve exceptional absorption. In this paper, a series of three-dimensional porous carbon·@PANI (polyaniline) composites were synthesized via facile roasting and subsequent coating process. The morphology, nanostructure and EM wave absorption properties of porous carbon@PANI (PC@PANI) were discussed in detail. Obviously, porous carbon derived from EDTA-2Na coated by PANI (PC@PANI-2) composites exhibited significantly enhanced EM wave absorption performance compared to pure porous carbon. The widest absorption bandwidth (RL

Fabrication of hierarchically porous structured PDMS composites and their application as a flexible capacitive pressure sensor

Abstract: Pressure sensors for wearable electronics are mounted on irregular surfaces and exposed to various external stimuli. Therefore, the sensor should have a flexible structure and wide pressure measurement range along with high sensitivity. In this study, we fabricated hierarchically porous structured polydimethylsiloxane (PDMS) composites with a simple and cost-effective method using sugar particles and a water-in-oil emulsion. Hierarchically porous PDMS composites were employed as the dielectric layers of flexible capacitive pressure sensors. The capacitive pressure sensor presents a sensitivity 22.5 times higher (0.18 kPa−1) than the sensors using bulk PDMS with a wide measurement range (0–400 kPa). The finite element analysis was implemented to analyze the non-linearity of sensors by observing the compressive behavior of the PDMS composites. For the practical applications, finger attached-sensor, respiration monitoring system, and sensor array were tested, and the proposed sensors showed sufficient potential for application in wearable electronics.

3D flower-like Co-based oxide composites with excellent wideband electromagnetic microwave absorption

Abstract: Transition metal oxides because of their excellent dielectric properties have been population for electromagnetic wave absorption application. In this paper, through two-step synthesis, hollow CoSnO3 was in-situ growth between layers of self-assembled flower-like ZnCo2O4 in the solvothermal process. The multi-layer sheet structure of ZnCo2O4 nanoflowers provides growth space for CoSnO3, which can increase interface polarization and natural resonance. Hybrid structure expands the propagation path of electromagnetic waves and the times of reflections and scattering. By adjusting the content of the growing process of CoSnO3, the maximum reflection loss (RL) at 12.4 GHz was −56.0 dB, and the wide effective absorption bandwidth (EAB) of 6.24 GHz (RL

Advanced honeycomb designs for improving mechanical properties: A review

Abstract: Honeycombs are ultra-light materials with outstanding mechanical properties, which mainly originate from their unit cell configurations rather than the properties of matrix materials. Honeycombs are triggering in numerous promising applications in the fields of architecture, automotive, railway vehicle, marine, aerospace, satellite, packaging and medical implants, etc. Here we provide an in-depth overview of some important advances in basic structural design to obtain novel honeycombs with various improved mechanical properties. Firstly, the review introduces the classical honeycomb configurations. Then, a clear classification of advanced designs is established and discussed according to the design scale. The designs on the macro scale are divided into hierarchical, graded and disordered, while the designs on the meso scale are grouped as hybrid, curved ligament and reinforced strut. Moreover, the effects of different designs on the mechanical properties of honeycomb are discussed quantitatively. Finally, we summarize the important potential designs to improve the mechanical properties of honeycombs and the challenges in further research.

Constructing flower-like core@shell MoSe2-based nanocomposites as a novel and high-efficient microwave absorber

Abstract: To effectively utilize the unique properties of layered transition metal dichalcogenide and the attractive morphology of hierarchical flower for the attenuation of electromagnetic wave, herein, high-efficiency flower-like core@shell structure FeSe2@MoSe2 nanocomposites were firstly synthesized through a simple in situ hydrothermal reaction on the surfaces of Fe3O4 nanoparticles with the adequate amounts of Mo and Se sources. The obtained results indicated that the designed flower-like core@shell structure FeSe2@MoSe2 nanocomposites with the filler loadings of 30 wt% and 40 wt% presented the optimal reflection loss (RLopt) value of −59.87 dB at 11 GHz with a matching thickness of 3.10 mm and −60.53 dB at 13.52 GHz with a matching thickness of 2.47 mm. And their corresponding effective frequency bandwidth (fb) values were up to 10.0 GHz with a thickness of 3.66 mm and 6.00 GHz with a thickness of 2.12 mm, respectively. It was worth pointing out that the as-prepared flower-like FeSe2@MoSe2 nanocomposite with filler loading of 30 wt% could simultaneously present very extraordinary electromagnetic wave absorption capabilities and broad absorption bandwidth with the very thin matching thicknesses, which was desirable for high-efficient microwave absorbers. Therefore, a simple and effective strategy was proposed to produce flower-like core@shell structure MoSe2-based nanocomposites, which could be applied as the very desirable candidates for high-performance microwave absorption materials.

3D printing of PLA/n-HA composite scaffolds with customized mechanical properties and biological functions for bone tissue engineering

Abstract: Bone defect caused by trauma, tumor, infection, and other reasons is a thorny problem that needs to be solved in orthopedic clinic. Customized bone repair biomaterials and their fabrication still need to be explored. Three-dimensional (3D) printing is a high-speed fabrication process for bone tissue biomaterials, which paves the way of solving clinical bone defect problems in a new way. In this study, the fused deposition modeling (FDM) technology was used to prepare the composite scaffolds of polylactic acid (PLA) and nano-hydroxyapatite (n-HA). The composite scaffold was optimized by material characterization, mechanical property test, and in vitro bone marrow mesenchymal stem cells biocompatibility test. Finally, a rabbit model was established to evaluate the osteogenic ability of PLA/n-HA scaffolds in vivo. The results showed that the PLA/n-HA composites proposed in this study were highly printable, and the printed scaffold showed tunable mechanical strength accompanied by the proportion of n-HA components. The biocompatibility and osteogenic induction properties were proved better than that of the pure PLA scaffold. This composite scaffold of PLA and n-HA provides a promising strategy for the repair of large bone defects.

Recent advances in biomedical engineering of nano-hydroxyapatite including dentistry, cancer treatment and bone repair

Abstract: Hydroxyapatite (HAp) has significant biological activity, degradability, and osteoconductivity. In recent decades, it has been widely used in dentistry, anti-tumour drug carriers, and orthopaedic repair. However, hydroxyapatite has limit features which are poor mechanical properties for directly inducing tooth enamel remineralization, particle size and morphology issues on drug delivery and brittleness for bone transplantation. This article summarizes the problems encountered in the preparation, application, and modification of hydroxyapatite in the above-mentioned fields and the current research progress, combining theory with experiment. Therefore, the greatest significance of this review is to comprehensively integrate and argue the forms and effects of nHA-based biomaterials, which provides a theoretical basis for the application of this material and help readers have clear insights into future research.

3D printing for polymer/particle-based processing: A review

Abstract: The 3D printing method, alternatively known as additive manufacturing (AM), is promising for rapid tooling and layered micromanufacturing. However, significant fundamental research and applied study in the 3D printing area are still necessary to develop new manufacturing mechanisms for combining multi-materials for multiscale and multi-functionality behaviors. Among those materials, particles with unique mechanical, thermal, electrical, optical, and other functional properties can find broad applications in structural composites, thermal packaging, electrical devices, optoelectronics, biomedical implants, energy storage, filtration, and purification. This review will first briefly cover the 3D printing basics before presenting the critical factors in polymer/particle-based printing. We will then introduce a spectrum of different printing mechanisms, i.e., vat polymerization-based, jetting-based, material extrusion-based, powder bed fusion-based, and a few other less utilized 3D printing methods, with a summary of the processing parameters, advantages, disadvantages, and future challenges of each printing technique. During this discussion of 3D printing, we will also present generally used polymers and particles, namely, liquid monomers, viscous inks, compliant gels, stiff filaments, and loosely packed pellets containing micro and nanoscale particles. The emphasis of this review is on the general printing mechanisms applicable in particle- and polymer-relevant processing. To end, this review identifies provides future perspectives regarding some new application examples. Identifying challenges in materials science and manufacturing processes will give direction to the fabrication of multifunctional systems for diverse applications, especially when using multi-materials (e.g., polymers and particles) at multiple scales (e.g., nanoscale morphologies and macroscale structures) for multifunctional systems.

Interface formation and bonding control in high-volume-fraction (TiC+TiB2)/Al composites and their roles in enhancing properties

Abstract: As interfaces play a more important role in high-volume-fraction ceramic/metal composites because of containing more hetero-phase interfaces, it is a great challenge to control the interfaces in such composites to balance their strength and plasticity and to obtain high performances. In this work, 50–60 vol% (TiC + TiB2)/Al composites were fabricated in Al–Ti–B4C system via a one-step method of reaction and densification, and their interface bonding and mechanical properties were compared with those of in-situ TiC/Al composites. Apparently, the defects, such as interfacial discontinuity, macro-pores, coarsening and agglomeration of particles, caused by increased ceramic content in the TiC/Al composites, are eliminated in the (TiC + TiB2)/Al composites using Al–Ti–B4C system. The 60 vol% (TiC + TiB2)/Al composite exhibits significantly enhanced mechanical properties, i.e. 70.5%, 60.7% and 69.8% respectively higher yield strength, ultimate compressive strength and plastic strain than 60 vol% TiC/Al composite. Such enhanced mechanical properties are attributed to the improvement in interface bonding strength and therefore the increase in the energy dissipation of crack propagation. The formation of enhanced interface in the (TiC + TiB2)/Al composites results from the reduction in the reaction heat in the Al–Ti–B4C system, improved crystallographic match and improved adhesion work between ceramic particles and matrix. This work may provide a new idea for the design and control of interfaces in high-volume-fraction ceramic-metal composites.

MXene as emerging nanofillers for high-performance polymer composites: A review

Abstract: MXenes, transition metal carbide and nitrides with graphene-like structures, have received numerous attention since they were synthesized from MAX phases in 2011. As a rising star in 2D material family, MXenes exhibit charming physical and chemical properties. The superiority in 2D flak structure, combined with rich functional groups, endows MXenes abundant tunable performance and also makes them show unique advantages in various fields. Furthermore, the special structural and functional features also make MXenes and MXene-based materials easy to combine with polymer matrices to meet its high-performance requirements in electrical, thermal, mechanical and other fields. Now, a variety of synthetic methods of MXenes have been explored to suit different application, from hydrofluoric acid to fluorinate-containing acid solution and fluorinate-containing salts. Moreover, diverse modification methods were studied based on abundant terminations of MXene, which are also reviewed. In addition, the fabrication method and performances of MXene/polymer composites are also invested to explore the influence of MXenes on the properties of composite materials. Subsequently, the applications of MXene-based polymeric composites with different properties were also reviewed to explore their application prospects. Lastly, based on current development situation of MXenes, the challenges and prospects for the development of MXene/polymer composites are discussed. In view of the splendid performance of MXenes, obviously, it is certain that MXenes would play a vital role in polymer composites and bring considerable prospects for the development of high-performance composite materials.

A review of artificial neural networks in the constitutive modeling of composite materials

Abstract: Machine learning models are increasingly used in many engineering fields thanks to the widespread digital data, growing computing power, and advanced algorithms. The most popular machine learning model in recent years is artificial neural networks (ANN). Although many ANN models are used in the constitutive modeling of composite materials, there are still some unsolved issues that hinder the acceptance of ANN models in the practical design and analysis of composite materials and structures. Moreover, the emerging machine learning techniques are posing new opportunities and challenges in the data-based design paradigm. This paper aims to give a state-of-the-art literature review of ANN models in the constitutive modeling of composite materials, focusing on discovering unknown constitutive laws and accelerating multiscale modeling. This review focuses on the general frameworks, benefits, and challenges and opportunities of ANN models to the constitutive modeling of composite materials. Moreover, potential applications of ANN-based constitutive models in composite materials and structures are also discussed. This review is intended to initiate discussion of future research scope and new directions to enable efficient, robust, and accurate data-driven design and analysis of composite materials and structures.

Micro-porous MXene/Aramid nanofibers hybrid aerogel with reversible compression and efficient EMI shielding performance

Abstract: Currently, extensive utilization of electronic devices and wireless equipment require human to take affirmative measures to weaken unwanted electromagnetic wave radiations. Herein, micro-porous structure MXene/aramid nanofibers hybrid aerogel was developed from aramid nanofibers and MXene(Ti3C2Tx) flakes through freeze-drying approach. The robust aramid nanofibers established foundation for oxidation protection and reversible compressibility in skeleton. Due to the unique micro-porous structure, the MXene(Ti3C2Tx)/aramid nanofibers hybrid aerogel remained efficient shielding capacity, whose electromagnetic interference (EMI) shielding effectiveness and specific EMI shielding effectiveness reached ~56.8 dB and 3645.7 dB cm2 g−1 at thickness of 1.9 mm in X-band. Furthermore, the shielding performance could be regulated by MXene(Ti3C2Tx) content and thickness. With increasing MXene(Ti3C2Tx) loading, the porous size of MXene(Ti3C2Tx)/aramid nanofibers hybrid aerogel enlarged, and the MXene(Ti3C2Tx)/aramid nanofibers hybrid aerogel became tough and robust. Under 40% strain, the maximum compressive stress of MXene(Ti3C2Tx)/aramid nanofibers hybrid aerogel with 21 wt% MXene(Ti3C2Tx) flakes content reached ~210 kPa. This work provided feasible avenue for fabricating hybrid aerogel with reversible compressibility and efficient EMI shielding performance simultaneously.

Enhancing strength-ductility synergy and mechanisms of Al-based composites by size-tunable in-situ TiB2 particles with specific spatial distribution

Abstract: The increase in strength usually accompanies by the sacrifice of ductility in the composites. This work proposed a strategy of design and synthesis of in-situ TiB2 particles to effectively tailor the microstructures and to enhance the mechanical performance of Al–Si-based composites. The tuning mechanisms for size and morphology of TiB2 particles were investigated by combustion synthesis in the Al–Ti–B reaction system. The nano/submicron-sized TiB2 particles with desirable morphology were then specially selected to construct high-performance Al–Si-based composites. Thanks to the strong interface bonding with a low crystallographic mismatch, TiB2 particles significantly refined the primary α-Al dendrites, eutectic Si and θ’ precipitates in the composites, which were 79.2%, 51.9% and 37.6% respectively smaller than those of the matrix. Numerical modeling results suggested that submicron-sized TiB2 particles were more likely to be engulfed or serve as heterogeneous sites while nano-sized TiB2 particles would be repulsed to the solid/liquid interface to physically restrict the growth of α-Al dendrites. The strength-ductility trade-off dilemma was broken therefore superior mechanical properties were obtained in the composites. This work provides a novel perspective for manipulating Al–Si-based alloys in terms of avoiding poisoning and achieving microstructural refinement and outstanding strength-ductility synergy.

Microstructure evolution and mechanical properties of in-situ Ti6Al4V–TiB composites manufactured by selective laser melting

Abstract: In-situ TiB reinforced titanium matrix composites (TMCs) were fabricated by selective laser melting (SLM) of ball-milled Ti6Al4V–TiB2 powders. Optimized SLM processing and stress relief annealing were applied to obtain crack-free and fully dense composites. TiB reinforcement is mainly present in the form of whisker clusters and exhibits a quasi-continuous distribution in TMC1 (2 vol%TiB) while a full-continuous distribution in TMC2 (5 vol%TiB). The distribution of TiB whisker clusters in primary β-Ti grain is not consistent with the complete dissolution mechanism proposed previously. As a result, a dual mechanism of direct reaction and precipitation has been put forward to describe the formation of TiB phase. The microhardness, compressive strength and tensile strength of TMC1 are improved by 14%, 36%, 25% respectively, compared with those of Ti6Al4V alloy. These enhancements can be mainly attributed to Hall-Petch strengthening and load-bearing transformation strengthening. The fracture surface of TMC1 after tensile testing shows a mixture of regions of cleavage facets with regions of small dimples.

Additive manufacturing of polymeric composites from material processing to structural design

Abstract: Polymeric composites with multi-functionality offer significant advantages over metals, including lightweight, high strength and stiffness, corrosion and fatigue resistance, etc. Additively manufactured composites draw intensive attention over the past decade due to that they exhibit the large potential to extend their applications from rapid prototyping to functional end-use components. Moreover, advances in additive manufacturing (AM) open new perspectives for the next generation of design and manufacturing of composites, which possess spatially digitalized and materialized arrangement of material/structure in a voxel-by-voxel manner. This review examines the work performed in this fast-growing field and elaborates its future perspectives and potentials. Specifically, the polymer AM processes incorporating different types of reinforcements are discussed in terms of mechanism, feedstocks, their advantages, and constraints. Then, the AM-driven designs for polymeric composites on multiscale and for multi-functional applications are emphasized. Further, emerging research topics including digital composites, intelligence/data-driven design approaches, and four-dimensional printing are further addressed with the careful analysis of existing gaps and future research trends. Finally, this review is concluded with an outlook on future research opportunities on AM-fabricated composites from design to fabrication. This review aims to provide a comprehensive guide to the stakeholders who want to utilize or develop an AM process for polymeric composites.

Recent advances in carbon-based nanomaterials for flame retardant polymers and composites

Abstract: An urgent need is to reduce the flammability of polymers and manage their toxic thermal decomposition products. Although conventional halogenated, metallic and phosphorus-based flame retardants (FRs) proved effective, they are known to cause major damage to human health and the environment. Containing carbon nanomaterials as a new class of flame retarding additives, polymer nanocomposites have displayed high flame retardancy, mechanical performance and electrical and thermal conductivity – a feat unmatched by conventional FRs. In this article we review very recent advances in carbon nanomaterials as FRs for polymers and composites as well as new understanding of the underpinning flame retarding mechanisms. Carbon nanomaterials, i.e. graphene, carbon nanotubes and carbon black, are discussed as the alternatives to conventional fillers due to their effectiveness in improving the polymers' flammability, mechanical properties and conductivity. The synergy between carbon-based nanofillers and conventional FRs is comprehensively reviewed, concluding that adding small fractions of carbon nanomaterials with conventional FRs into polymers can not only synergistically improve the flame retardancy but result in multifunctionalities such as thermal and electrical conductivity, without compromising the polymers’ mechanical performance. Chemically or physically combining carbon nanomaterials with other compounds or nanoadditives containing phosphorus and nitorgen elements can create significant synergies for multifunctional polymers and composites to attain superior flame-retardant properties.

A review on recycling and reuse methods for carbon fiber/glass fiber composites waste from wind turbine blades

Abstract: The development of novel strategies for recycling and reusing fiber composites is driven by various environmental and economic factors. Recycling materials mean that materials are processed with feasible processing methods or environment-friendly methods without deterioration of mechanical or physical performance enabling their reuse. Recycling end-of-life (EOL) waste of wind turbine (WT) blade composites is a critical challenge for renewable energy sector. This paper reviews various recycling methods (mechanical, thermal, chemical, and hybrid) and reuse of reclaimed fiber composites of carbon and glass fibers. Physical, mechanical, and chemical properties of recovered fibers and new composites (made of recovered fibers) have been discussed in detail. This paper aims to find out the optimum recycling process from existing recycling methods to recycle EOL waste of WT blades. Glass fibers (GFs) and carbon fibers (CFs) are energy-intensive to manufacture, which means these have high recycling capability in terms of the environment as well as an economic perspective. Challenges in the recycling of fibers have been identified from the available literature; future research possibilities with promising values of recovered fibers to reuse in some high-value structural applications have been highlighted.

Direct ink writing (DIW) of structural and functional ceramics: Recent achievements and future challenges

Abstract: Along with vast research on the additive manufacturing (AM) of polymeric and metallic materials, three-dimensional (3D) manufacturing of ceramic materials is now the modern trend. Among all the additive manufacturing techniques, Direct Ink Writing (DIW) permits the ease of design and rapid manufacturing of ceramic-based materials in complicated geometries. This paper presents an outline of the contributions and tasks in the fabrication 3D ceramic parts by the DIW technique. The current state-of-the-art manufacturing of various ceramics such as alumina, zirconia, and their composites through Direct Ink Writing (DIW) is described in detail. Moreover, this review paper aims at the innovations in the DIW approach of ceramic materials and introduces the progression of the DIW for the manufacturing of ceramics. Most importantly, the DIW technique has been explained in detail with illustrations. The prospects and challenges related to the DIW technique are also underscored.

Lightweight and recoverable ANF/rGO/PI composite aerogels for broad and high-performance microwave absorption

Abstract: Graphene is regarded as an excellent microwave absorbing material due to its low density and adjustable dielectric properties. In this paper, aramid nanofiber/reduce graphene oxide/polyimide (ANF/rGO/PI) composite aerogels were successfully prepared by a two-step method of freeze-drying and annealing. ANF and PI enhance the bonding force between rGO sheets. The unique three-dimensional conductive network of rGO not only provides a transmission path for electrons, but also enhances multiple reflection and scattering for electromagnetic waves. The defects on the surface of rGO during annealing caused dipole polarization, and a large number of heterogeneous interfaces between ANF, rGO and PI enhance the interface polarization. Good dielectric properties and structure make the material have excellent microwave absorption properties. At 10.8 GHz, the minimum reflection loss (RLmin) reaches −41.0 dB, the effective absorption bandwidth covers the X-band, and the thickness is 5.1–6.9 mm. In addition, the material also exhibited good mechanical properties and heat resistance, and was expected to become a low-density, high-performance high-temperature microwave absorbing material.

MOF−Guest complex derived Cu/C nanocomposites with multiple heterogeneous interfaces for excellent electromagnetic waves absorption

Abstract: Electrical conductivity and interfacial polarization are two crucial factors to design high-performance electromagnetic absorption (EMA) materials, but how to synergistically balance these factors still remains to be difficult. In this work, we report the synthesis of Cu/C nanocomposites via the controlled pyrolysis of a MOF-guest complex. The prepared Cu/C nanocomposites are made up of cross-linked carbon network and various irregular particles. The carbon network provides appropriate electrical conductivity to contribute to the conductance loss. Multiple heterogeneous interfaces, such as Mo2C/C, Mo2C/CuO, CuO/C, Mo2C/Cu, and Cu/C interfaces, have been determined in these Cu/C nanocomposites, resulting in obviously improved polarization loss. As a result, the Cu/C nanocomposite exhibits excellent EMA performance, where the efficient absorption bandwidth reaches 6.8 GHz, and the maximal absorption gets to −52 dB. This research provides new idea to design high-performance EMA nanocomposites by tuning the electrical conductivity and interfacial polarization.

Research advances in composition, structure and mechanisms of microwave absorbing materials

Abstract: The earliest microwave absorbing materials (MAMs) are fabricated in the early 20th century for military purpose to inhibit radar detection. Currently, the application of MAMs has been existing in every part of human's life to prevent radiation and interference. The microwave absorbant and microwave absorbing coatings classified by composition including alloys, metal oxides, conductive polymers, carbon materials, ceramic materials both in traditional and innovative forms are introduced in this work. Considering the harsh and complex application environment, MAMs with high temperature resistance and infrared-compatible stealth performance are involved. Metamaterials, showing excellent electromagnetic properties which are far beyond that of the materials can achieve, including perfect absorber, digitally coded control metamaterials, bionic structural materials, and adjustable smart metamaterials, are also introduced specifically in this work. In addition, to investigate electromagnetic response of absorbant, the first-principles calculations works are overviewed. The electromagnetic properties, loss mechanisms, structure, fabrication method, regulation approaches, designing principles, current applications, and future prospects of MAMs are involved in this work. This work gives a comprehensively overview over the MAMs for their theoretical and experimental advances in recent years including the military radar (frequency range of 2–18 GHz) stealth materials, relevant infrared compatible (infrared-visible, infrared-radar, infrared-laser) stealth materials, and other stealth materials with multifrequency adaptability.

Use of recycled fibers in concrete composites: A systematic comprehensive review

Abstract: Municipal solid waste materials are growing worldwide due to human consumption. Nowadays, a different type of goods on large-scale is produced in the factories which is going to generate numerous amount of solid waste materials in the near future. Therefore, the management of these solid waste materials is a great concern around the world. Inadequate landfill, environmental pollution and its financial burden on relevant authorities, recycling and utilization of waste materials have a significant impact compared to disposing them. Studies have been done to reuse of waste materials as one of the elements of concrete composites. Each of the elements gives the concrete strength; however, the reuse of these wastes not only makes the concrete economical and sustainable, but also helps in decreasing environmental pollution. There are a number of different types of waste materials such as plastics, carpets, steels, tires, glass, and several types of ashes. In this paper, a comprehensive review was carried out on the influence of recycled plastic fibers (RPFs), recycled carpet fibers (RCFs) and recycled steel fibers (RSFs) on the fresh, mechanical and ductility properties of concrete. The previous studies were investigated to highlight the effects of these waste product fibers on the most important concrete properties such as slump, compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, ultrasonic pulse velocity, energy absorption, ductility, and toughness. In this regard, more than 200 published papers were collected, and then the methods of preparation and properties of these recycled fibers (RF) were reviewed and analyzed. Moreover, empirical models using mechanical properties were also developed. As a result, RPFs, RCFs and RSFs could be used safely in concrete composites due to it is satisfactory fresh, physical and mechanical properties.

Multi-yolk ZnSe/2(CoSe2)@NC heterostructures confined in N-doped carbon shell for high-efficient sodium-ion storage

Abstract: Transition metal selenides with low pollution, high chemical stability and high theoretical capacity are regarded as the most prospective candidate materials for sodium ions storage. However, its poor conductivity, drastic volume change and sluggish diffusion kinetics hinder potential commercialized practical applications. Herein, multi-yolk ZnSe/2(CoSe2) heterostructures confined in N-doped carbon (NC) hexahedron have been prepared via a facile two-step method. Benefiting from the novel multi-yolk-shell structure with heterojunction interfaces, ZnSe/2(CoSe2)@NC electrodes display superior sodium storage performance with superior cycling performance (specific capacity of 552.1 mAh g−1 over 100 cycles at 0.1 A g−1) and outstanding rate performance (specific capacity of 528.6 mAh g−1 at 5 A g−1) and long-term cycling stability. Our designed multi-yolk-shell ZnSe/2(CoSe2)@NC heterostructures can be envisaged to accelerate progress towards advanced alkali metal ion batteries with vast implications for commercialized high-performance energy-storage applications.

Recent progress and multifunctional applications of 3D printed graphene nanocomposites

Abstract: This review provides a comprehensive analysis of available peer-reviewed literature in which graphene and/or its derivatives are incorporated into a polymer matrix in order to enhance the final properties and functionalities of the three dimensional (3D) printed structure. Research in which graphene derivatives have been incorporated into plastic 3D printing technologies such as Fused deposition modeling (FDM), Stereolithography (SLA), Selective laser sintering, Inkjet 3D printing, Extrusion-based printing and Binder-jet printing is presented. For certain design requirements and applicability of the material, great care needs to be taken to select the appropriate printing method. Factors which play a key role in final performance of the printed parts are identified, including dispersion of graphene or its derivatives in matrix, interfacial interaction between graphene or its derivatives and matrix, printing orientation, nanofiller's aspect ratio, reduction of graphene oxide and ink viscosity. In fact, the multifunctional applications of the 3D printed structures based on graphene or graphitic filler composites open up the countless possibilities of current research. Although great progress has been made in exploring the mechanical, electrical, optical and thermal, characteristics of these materials, significant research and development need to be done to fully fetch their inherent potential. This article serves the purpose to researchers to improve latest research outcomes and explore new graphene–based nanocomposites for different applications.

A review of dental composites: Challenges, chemistry aspects, filler influences, and future insights

Abstract: Resin-based dental composites are promising tooth-resembling materials in restorative dentistry. The limited longevity of dental composite restorations due to the bulk/marginal fracture and secondary caries as well as possible health risks are the critical challenges faced by such materials. Therefore, developments of resin-based dental composites received considerable attention in academic researches for clinical applications. A comprehensive review of the recent developments in the scientific literature on resin-based dental composites is presented in this article. Firstly, in the article, the challenges in dental composites are introduced and then the chemical aspects of the systems are classified through a review of employed resins. Subsequently, the different characteristics related to the fillers employed for the development of the resin-based dental composites are described. Finally, conclusions are drawn and future insights are proposed. This article provides an insight that paves the way for tailoring and designing resin-based dental composites for clinical applications.

Advanced sandwich structures for thermal protection systems in hypersonic vehicles: A review

Abstract: A heat shield called the thermal protection system (TPS) is an important structure in hypersonic vehicles as it prevents hot air from entering vehicles and potential impacts from space debris. With the increase in demand for low-cost reusable launch vehicles as well as for searching and exploration of new planets in both unmanned and manned missions, the need for developing an effective TPS has increased across many countries. The structural design of TPSs has become more prominent in the early stage of hypersonic vehicle development. Sandwich structures that have the advantages of low density and high performance are integrated into the structural design of an effective TPS. This paper provides a comprehensive review of recent research efforts on sandwich structures for TPSs. The topics discussed in this paper include aspects of structural and material design, mechanical and thermomechanical performances, and manufacturing methods. In particular, we review and discuss the structural design as well as the material design of sandwich structures for different TPS types with various configurations, including corrugated cores, lattice cores, multilayer cores, foams, honeycomb cores, bio-inspired cores. The materials used for the sandwich structures, such as various types of laminated composite, ceramic matrix composite, and metals, are included. We also discuss the performance of the TPS sandwich structures in terms of temperature gradients, deformation limits, and mechanical strengths and provide a discussion on the manufacturing methods of TPS sandwich structures for hypersonic vehicles. Finally, further research directions and challenges of sandwich structures for TPSs are presented.