Carbon/Carbon Composite Friction Discs for Aerospace

Carbon/carbon friction discs are produced at Newmet Composites (a division of New Metals & Chemicals Ltd.) for flap jam systems in airplanes. They offer excellent mechanical and friction properties. New carbon/carbon composite grades have been developed at Newmet Composites during the last few years. Another material that is used for this applications is bronze. Different material grades and different designs are compared in this paper. The key‐properties discussed are compression strength, flexural strength and friction behaviour. The friction tests were simulating the friction behavior during the application of such discs. Compression tests were made to define the possible application: For the application in the flap jam system the compression strength has to be 207 MPa at the minimum, for other applications this is not necessarily required. A test described briefly in this paper was developed for flexural strength. The flexural strength is not very important during the application, but important when the discs are being handled and built in. It could be shown that both production parameters and design have a significant influence on the performance of carbon/carbon friction discs. These results are needed to define further applications for these materials. Finally the material carbon/carbon is briefly compared with alternative materials.     

Review of functionalization,structure and properties of graphene/polymer composite fibers

Fibrous materials usually have good mechanical, heat-resistant, acid-resistant, alkali-resistant and moisture regained properties which originate from its composition, condensed structure and crosslinking styles. However, these materials often lack of good electrical conductivity, flame retardance, anti-static and anti-radiation properties which are desired for varied specific applications. Graphene, as a new emerging nanocarbon material, has some unique properties including superb thermal and electrical conductivity, strong mechanical and anti-corrosive property, extremely high surface area etc. Therefore, graphene has attracted extensive interests in recent years. Upon modification with graphene, fibers exhibit a number of enhanced or new properties such as adsorption performance, anti-bacteria, hydrophobicity and conductivity which are beneficial for broader applications. In this review, the strategies to modify the fibers with graphene and the corresponding effects on the fibers as well as the relevant applications in varied areas were discussed.     

Microstructure-property relationships of GRP

Fibre-reinforced composite materials are being used increasingly in critical applications, when the primary function of the material is to support loads, but very high safety margins are commonly used for such applications. Such large safety margins arise from the uncertainties regarding the mechanical behaviour of composite materials. The authors believe that the lack of microstructural definition of composite materials may make a substantial contribution to these uncertainties. In this initial study, relationships are sought between microstructure and properties of a model microstructure. The methods used are applicable to a very wide range of composite materials.     

In vitro degradation and cytocompatibility evaluation of novel soy and sodium caseinate-based membrane biomaterials

Soy- and casein-based membranes are newly proposed materials disclosing a combination of properties that might allow for their use in a range of biomedical applications. Two of the most promising applications are drug delivery carrier systems and wound dressing membranes. As for all newly proposed biomaterials, a cytotoxic scanning must be performed as a preliminary step in the process of the determination of the compatibility with biological systems (biocompatibility). In this study, the cytotoxicity of both soy- and casein-based protein biomaterials has been evaluated and correlated with the materials degradation behavior. It was possible to show, through morphological and biochemical tests that these natural origin materials do not exert any cytotoxic effect over cells, and in some cases can in fact enhance cell proliferation. The different treatments to which the membranes were subjected during their processing (that include crosslinking with glyoxal and tannic acid, and physical modification by thermal treatment) seemed to have a clear effect both on the materials mechanical properties and on their in vitro biological behavior.     

CHEMICALLY BONDED CERAMIC TOOLING FOR ADVANCED COMPOSITES

The wide range of advanced composite forming methods has motivated the development of new tooling materials capable of surviving processing extremes. Chemically Bonded Ceramic (CBC) tooling media have been formulated to supply molds with the strength, durability and thermal properties required in these applications. These inorganic materials retain relatively low cost and fabrication times. They incorporate a wide range of aggregates, fibers and inserts, selected to provide tools with desirable thermal and physical properties. CBC tools have been successfully utilized to form parts at temperatures ranging from ambient to 1800° F and at pressures as high as 10,000 psi. Chemically Bonded Ceramic tooting media provide an innovative alternative when more traditional tooling materials lack stability, durability, heat transfer capabilities or formability. This paper presents an overview of some applications in which Chemically Bonded Ceramic tooling have been used, and compares these materials to others which are commonly used in composite forming processes.     

Polypropylene/glass fibre 3D-textile reinforced composites for automotive applications

Textile-reinforced thermoplastic composites offer huge application potentials for a rapid manufacturing of components with versatile possibilities of integrating functions. However, an application of these new materials requires the knowledge of the directional dependent material properties. In this study, results are presented concerning selected relevant load cases for industrial applications. For the new group of multi-layered flat bed weft-knitted glass fibre/polypropylene composites (MKF-GF/PP), tensile tests under different temperatures and test velocities have been carried out as well as Charpy impact tests, open hole tension tests and dynamic-mechanical analysis. The mechanical properties of MKF-GF/PP and unidirectional GF/PP composites with tailored fibre surface and interphase, respectively, have been compared to those of woven GF/PP composites and GF/PP composites made of non-crimp fabrics (NCF) as a benchmark.     

Graphene oxide and hydroxyapatite as fillers of polylactic acid nanocomposites: preparation and characterization

Graphene and its derivatives have attracted great research interest for their potential applications in electronics, energy, materials and biomedical areas. When incorporated appropriately, these atomically thin carbon sheets are expected to improve physical properties of host polymers at extremely small loading. Herein, we report a novel two-step method for the preparation of PLLA/Hap/graphene oxide nanocomposites with augmented mechanical properties when compared to PLLA/Hap and neat PLLA. The presence of graphene oxide (GO) had a positive effect on the dispersion of hydroxyapatite particles on the polymeric matrix contributing for a good homogeneity of the final nanocomposite. PLLA nanocomposites prepared with 30% (w/w) of Hap and 1% (w/w) of GO showed the highest hardness and storage modulus values indicating an efficient load transfer between the fillers and the PLLA matrix. These materials may find interesting biomedical applications as for example bone screws. The following step on the study of these materials will be in vitro tests to access the biocompatibility of these new nanocomposites.     

Comparing the mechanical performance of synthetic and natural cellular materials

This work compares the mechanical performance of agglomerated cork against synthetic materials typically used as impact energy absorbers. Particularly, the study will focus on the expanded polystyrene (EPS) and expanded polypropylene (EPP).Firstly, quasi-static compression tests are performed in order to assess the energy storage capacity and to characterize the stress–strain behavior cellular materials under study. Secondly, guided drop tests are performed to study the response of these materials when subjected to multiple dynamic loading (two impacts). Thirdly, finite element analysis (FEA) is carried out in order to simulate the compressive behavior of the studied materials under dynamic loading.Results show that agglomerated cork is an excellent alternative to the synthetic materials. Not only for being a natural and sustainable material but also for withstanding considerable impact energies. In addition, its capacity to keep some of its initial properties after loading (regarding mechanical properties and dimensions) makes this material highly desirable for multiple-impact applications.     

Hybrid nanocomposite materials for energy storage and conversion applications

Functional Hybrid materials based on conducting polymers and inorganic photo-electroactive species provide a wealth of opportunities for the development of novel materials with improved properties. Polyoxometalates are one type of well-known inorganic species with most interesting photo-electrochemical activity. They are perfect models for nanometer-sized oxide quantum-dots both concerning structure, topology and electrochemical and photochemical properties. Yet, they have not been applied as materials because of their molecular nature (i.e., soluble in most solvents or electrolytes). In our group we have recently developed a research line dealing with the integration of these fascinating clusters in conducting polymer matrices to yield functional hybrid materials. Our past emphasis was on electroactivity for energy-storage applications but these materials can also be used, as it is shown here, for photoelectrochemical applications.     

Static and dynamic characterization of composition cork for sandwich beam cores

Composition cork can be regarded as an interesting solution for light-damped sandwich panels. Despite the emergent interest on these materials for structural applications, there is a lack of information concerning its static and dynamic properties. This study presents a comparative study on a set of different experimental characterization methodologies applied on a selected agglomerated cork for vibration damping applications. The obtained results support the assumption of an air spring/viscous-based mechanism ruling the low-frequency behaviour of these materials. This assumed behaviour is a result from the observations of the cellular microstructure of natural and composition corks. Indicative values for the Young’s modulus, storage modulus and loss factor are provided as results from this study. In addition, a multilayer beam finite element, based on a mixed formulation, is proposed to be applied in an inverse characterization methodology and to be used also for the experimental validation tasks. The finite element proved to be efficient and accurate.     

Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades.Among these compounds,layered two-dimensional(2D)materials,such as graphene,black phosphorus,transition metal dichalcogenides,IVA–VIA compounds,and MXenes,have generated a large research attention as a group of potentially high-performance thermoelectric materials.Due to their unique electronic,mechanical,thermal,and optoelectronic properties,thermoelectric devices based on such materials can be applied in a variety of applications.Herein,a comprehensive review on the development of 2D materials for thermoelectric applications,as well as theoretical simulations and experimental preparation,is presented.In addition,nanodevice and new applications of 2D thermoelectric materials are also introduced.At last,current challenges are discussed and several prospects in this field are proposed.     

Metal matrix composites. A bird’s eye view

Composite materials, in general, have so far been used mainly for structural applications. However, with regard to metal matrix composites, interest is growing on account of their physical properties. Indeed, customer requirements in this field cannot always be met by traditional materials. This paper first presents a brief overview of the interaction between fabrication, microstructure and properties of metal matrix composites. Further, some changes in the strategy for modelling and designing these materials are discussed. Finally, future prospects are outlined.     

Advanced materials for neural surface electrodes

Designing electrodes for neural interfacing applications requires deep consideration of a multitude of materials factors. These factors include, but are not limited to, the stiffness, biocompatibility, biostability, dielectric, and conductivity properties of the materials involved. The combination of materials properties chosen not only determines the ability of the device to perform its intended function, but also the extent to which the body reacts to the presence of the device after implantation. Advances in the field of materials science continue to yield new and improved materials with properties well-suited for neural applications. Although many of these materials have been well-established for non-biological applications, their use in medical devices is still relatively novel. The intention of this review is to outline new material advances for neural electrode arrays, in particular those that interface with the surface of the nervous tissue, as well as to propose future directions for neural surface electrode development.     

Low cycle fatigue behavior of Ti6Al4V thermochemically nitrided for its use in hip prostheses

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Besides, titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes difficult the use of titanium and Ti6Al4V in some biomedical applications, like articulating components of prostheses. Some surface treatments are available in order to correct these problems, like thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Low cycle fatigue behavior in air of Ti6Al4V alloy has been studied. Results show a reduction of low cycle fatigue life up to 10% compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.     

雷达与红外兼容隐身材料的研究及进展

雷达与红外兼容隐身材料在军事领域具有广阔的应用前景.综述了对雷达与红外兼容隐身材料的研究状况及应用,详细分析了粘结剂对材料隐身性能的影响以及半导体填料对实现雷达与红外兼容隐身的可能性.     

Physical and mechanical properties of foamed Portland cement composite containing crumb rubber from worn tires

The management of worn tires is a concern in industrialized countries. The application of crumb rubber as lightweight aggregate in cement based materials is a green alternative for reusing this material. High replacements of natural sand by crumb rubber were studied and an air-entraining agent was employed to ensure a cellular structure in the cement-based composite. The obtained results from tests in fresh state reveal an improvement in workability. The tests conducted on hardened composite show promise for constructive applications where thermal and acoustic properties are required. The minimum requirement of mechanical strength for masonry units was achieved, since compressive strengths varied between 1 and 10 MPa. Finally, potential applications as a construction material have been highlighted.     

Emerging Trends in Terahertz Metamaterial Applications

The terahertz spectrum of electromagnetic waves is finding its position in various applications of day to day life because of its unique properties, including the penetration through opaque materials. Naturally occurring materials in this range are rare due to the display of a natural breakpoint of both electric, and magnetic resonances in these materials. However recent advances in artificially engineered materials, which show resonance in this region are able to harness desirable properties in the terahertz region. In this paper, terahertz design and fabrication issues have been explored along with their applications. A brief review of metamaterial terahertz applications has been carried out including metamaterial absorbers, filters, modulators, switches, lenses, and cloaking structures. The various patterns of metamaterial unit cells are discussed elaborately along with the possibility of flexible active terahertz structures.     

Mid-infrared photonics and optoelectronics in 2D materials

With intriguing properties that are different from the conventional bulk materials, two-dimensional (2D) materials have attracted numerous and widespread research interests, including its applications in photonics and optoelectronics. Devices based on 2D materials have been demonstrated in a wide spectral range, from the ultraviolet to the terahertz, and the microwave wavelength range. The mid-infrared (MIR) region (about 2–20 μm) bears a particular scientific and technological significance because, for instance, many molecules have their spectral fingerprints and there are atmosphere transparent windows in this region. Nevertheless, the MIR region remains underdeveloped compared to the visible and the near-infrared telecommunication regimes, mainly due to the lack of suitable materials, such as narrow bandgap materials, and proper photonic designs for building high performance optoelectronic devices in this wavelength regime. Therefore, researchers have been exploring the possibility and opportunity of 2D materials to fill up the gap. Here, we review the key recent developments of 2D materials in the MIR photonic and optoelectronic applications, including photodetection, light modulation, surface plasmon polaritons, phonon polaritons, and their nonlinearities and provide an outlook on the challenges and opportunities that lie ahead for MIR optoelectronic research fields with 2D materials.     

Review of nanocarbon-engineered multifunctional cementitious composites

As structural materials, cementitious materials are quasi-brittle and susceptible to cracking, and have no functional properties. Nanotechnology is introduced into cementitious materials to address these issues. Nano materials, especially nano carbon materials (NCMs) were found to be able to improve/modify the mechanical property, durability and functional properties of cementitious materials due to their excellent intrinsic properties and composite effects. Here, this review focuses on the recent progress of fabrication, properties, and structural applications of high-performance and multifunctional cementitious composites with NCMs including carbon nanofibers, carbon nanotubes and nano graphite platelets. The improvement/modification mechanisms of these NCMs to composites are also discussed.