A review on lightweight materials for defence applications:Present and future developments

The defence sector is now at an advanced level,catering to the global scenario,and countries also invest heavily in research and development.Countries around the world have spent a lot of money on research and development over the years in order to stay ahead of their competitors.Lightweight materials are critical in defence applications because they allow components to be lighter without sacrificing strength.This review provides an overview of the research related to defence applications.The book provides comprehensive details on current trends in the application of lightweight materials in defence.This review also includes historical and current perspectives on defence technologies.It discusses uses of lightweight materials such as metal matrix composites,polymer composites,ceramic matrix composites,fiber composites in defence sectors Finally,the review paper also emphasizes future military applications of lightweight materials.

Effect of Pyrophyllite Addition on Properties of Lightweight Insulation Refractory Materials

To solve the problem of over-high density of lightweight insulation refractory bricks prepared with fly ash, new lightweight insulation refractory materials with density 〈 0. 89 g · cm^-3 were .synthesized using pyrophyl-lite, .fly ash, and Suzhou clay as the main starting materials and saw dast as the pore forming substance, and controlling the addition of the pyrophyllite （20%, 30% , and 40% by mass ） and the treating temperature （1 250, 1 300, 1 350, and 1 400 ℃ ）. The synthesized materials were characterized by the XRD, SEM and the thermal conductivity measuring in.strument. The results show at pyrophyllite addition of 30% and treat temperature of l 400 ℃ , the material can achieve linear shrinkage of 6. 6%, apparent porosity of 57%, bulk density of 0. 75 g · cm^-3, compressive strength of 2.7 MPa, and thermal conductivity at 350 ℃ of 0. 152 -0. 216 W·（ m·K）^-1.This indicates that the pyrophyllite decomposition at high temperatures forms mullite and amorphous quartz introducing volume expansion, which counteracts some shrinkage at high temperatures. So it is feasible to use pyrophyllite, fly ash waste and clay to prepare lightweight insulation refractory materials.

Preparation of Periclase-forsterite Lightweight Heat-insulating Refractories by Molten Salt Method

Low grade magnesite is one of the main research directions in the future as the raw material for the preparation of magnesia based insulating refractories.Periclase-forsterite(MgO-Mg_(2)SiO_(4)) lightweight insulating refractories were prepared by the molten salt method with high silica magnesite and tertiary talc ore as raw materials by pretreating them to get light burnt magnesia and talc,and NaCl molten salt as the reaction medium.The effects of the NaCl addition,the sintering temperature,the holding time and the raw material ratio on the sample preparation were studied.The results show that when the NaCl addition is 20% of the mass of light burnt magnesia and talc mixture,the sintering temperature is 1 200 ℃,the holding time is 6 h,and m(light burnt magnesia):m(talc)=5:5,the sample has the optimal comprehensive properties:the bulk density of 1.46 g·cm^(-3) and the apparent porosity of 55.0%.In addition,it is found that self-decomposition of talc and the formation of forsterite can form pores inside the sample.

Recent innovations in laser additive manufacturing of titanium alloys

Titanium(Ti)alloys are widely used in high-tech fields like aerospace and biomedical engineering.Laser additive manufacturing(LAM),as an innovative technology,is the key driver for the development of Ti alloys.Despite the significant advancements in LAM of Ti alloys,there remain challenges that need further research and development efforts.To recap the potential of LAM high-performance Ti alloy,this article systematically reviews LAM Ti alloys with up-to-date information on process,materials,and properties.Several feasible solutions to advance LAM Ti alloys are reviewed,including intelligent process parameters optimization,LAM process innovation with auxiliary fields and novel Ti alloys customization for LAM.The auxiliary energy fields(e.g.thermal,acoustic,mechanical deformation and magnetic fields)can affect the melt pool dynamics and solidification behaviour during LAM of Ti alloys,altering microstructures and mechanical performances.Different kinds of novel Ti alloys customized for LAM,like peritecticα-Ti,eutectoid(α+β)-Ti,hybrid(α+β)-Ti,isomorphousβ-Ti and eutecticβ-Ti alloys are reviewed in detail.Furthermore,machine learning in accelerating the LAM process optimization and new materials development is also outlooked.This review summarizes the material properties and performance envelops and benchmarks the research achievements in LAM of Ti alloys.In addition,the perspectives and further trends in LAM of Ti alloys are also highlighted.

Time lapse in situ X-ray imaging of failure in structural materials under cyclic loads and extreme environments

Damage evolution characterization and performance evaluation under realistic conditions are essential to ensure reliable operation of critical safety components.However,previous studies focus on the surface detection because of very limited penetration capacity of nondestructive testing facilities.Here,we review the recent progress of material damage mechanism by various in situ testing rigs that are compat-ible with laboratory and synchrotron radiation X-ray facilities.Then,taking metallic alloys and composites as model materials,we demonstrate the unique advantages of in situ X-ray three-dimensional tomography in unveiling complex failure mechanisms,quantifying crack growth driving forces and crack closure phenomena,and elucidating the strengthening/degrading effects from microstructure and environment on structural material degradation.Finally,we also discuss the ongoing direction of in situ multi-scale visualization and characterization with the development of advanced high-energy X-ray facilities,the improvement of in situ devices and sample environments,the demand of high-throughput tests,and the processing and application of massive test data.

Lightweight foam-like nitrogen-doped carbon nanotube complex achieving highly efficient electromagnetic wave absorption

With the increased electromagnetic wave(EMW)threat to military and human health,the develop-ment of EMW-absorbing materials is crucial.Metal-organic framework derivatives containing magnetic nanoparticles and a carbon matrix are potential candidates for designing efficient EMW-absorbing mate-rials.Herein,a zeolitic imidazolate framework-67(ZIF-67)-embedded three-dimensional melamine foam is pyrolyzed to afford carbon foam-based nitrogen-doped carbon nanotube composites,named 3D foam-like CoO/Co/N-CNTs.Magnetic CoO/Co particles are confined in the dielectric carbon nanotube skeleton.The carbon nanotubes provide considerable conductive loss,while CoO/Co magnetic particles are con-ducive to providing magnetic loss and adjusting impedance matching.Moreover,the numerous defect structures introduced by heteroatomic doping(nitrogen)cause dipole polarization and simultaneously adjust impedance matching.Meanwhile,the unique porous nanotube structure promotes multiple re-flections and scattering of EMWs,further optimizing impedance matching.CoO/Co/N-CNTs composites exhibit a minimum reflection loss of−52.3 dB at a matching thickness of 2.0 mm,while the correspond-ing effective absorption bandwidth is 5.28 GHz at a matching thickness of 2.2 mm.This study reports a novel approach to fabricating a lightweight high-performance EMW-absorbing material.

Construction utilization of foamed waste glass

Foamed waste glass(FWG) material is newly developed for the purpose to utilize the waste glassware and other waste glass. FWG has a multi-porous structure that consists of continuous or discontinuous voids. Hence lightweight but considerable stiffness can be achieved. In the present study, the manufacture and engineering properties of FWG are introduced first. Then, the utilizations of FWG are investigated in laboratory tests and field tests. Some case studies on design and construction work are also reported here. Through these studies we know that the discontinuous void material can be utilized as a lightweight fill material, ground improvement material and lightweight aggregate for concrete. On the other hand, the continuous void material can be used as water holding material for the greening of ground slope and rooftop, and as clarification material for water.

The Effective Surface Metallization of Hollow Glass Microspheres for Flexible Electromagnetic Shielding Film

The surface of hollow glass microspheres (HGMs) was roughened by a HCl+NH_(4)F strategy,which achieved a broken ratio as 16.10%,and then metallized by electroless plating by Co nanoparticles up to 90 wt% (abbreviated as Co-HGMs).The average grain size of Co was measured to range from 0.4 to 0.5 μm.Then Co-HGMs were mixed with liquid silicone rubber and xylene,and cured on a perspex plate applicable for flexible electromagnetic shielding.By attentive parameter optimization,a film about 0.836 mm in thickness was obtained with a density of 0.729 g/cm^(3),showing a shielding effectiveness of 15.2 dB in the X-band (8.2-12.4 GHz) at room temperature,which was ascribed to the formation of a conductive network of Co-HGMs inside the film.Simultaneously,the tensile strength of 0.89 MPa at an elongation ratio of 194.5% was also obtained,showing good mechanical properties and tensile strength.

Light-weighting in aerospace component and system design

Light-weighting involves the use of advanced materials and engineering methods to enable structural elements to deliver the same,or enhanced,technical performance while using less material.The concept has been extensively explored and utilised in many industries from automotive applications to fashion and packaging and offers significant potential in the aviation sector.Typical implementations of light-weighting have involved use of high performance materials such as composites and optimisation of structures using computational aided engineering approaches with production enabled by advanced manufacturing methods such as additive manufacture,foam metals and hot forming.This paper reviews the principal approaches used in light-weighting,along with the scope for application of light-weighting in aviation applications from power-plants to airframe components.A particular area identified as warranting attention and amenable to the use of lightweighting approaches is the design of solar powered aircraft wings.The high aspect ratio typically used for these can be associated with insufficient stiffness,giving rise to non-linear deformation,aileron reversal,flutter and rigid-elastic coupling.Additional applications considered include ultralight aviation components and sub-systems,UAVs,and rockets.Advanced optimisation approaches can be applied to optimise the layout of structural elements,as well as geometrical parameters in order to maximise structural stiffness,minimise mass and enable incorporation of energy storage features.The use of additive manufacturing technologies,some capable of producing composite or multi-material components is an enabler for light-weighting,as features formally associated with one principal function can be designed to fulfil multiple functionalities。

ZnO/nitrogen-doped carbon nanocomplex with controlled morphology for highly efficient electromagnetic wave absorption

In this work,zeolitic imidazolate framework-8(ZIF-8)with yolk-shell and hollow structures were pre-pared by a convenient chemical etching method.A subsequent pyrolysis of ZIF-8 enabled one to pro-duce ZnO/nitrogen-doped carbon nanocomplexes with original ZIF-8 morphology,where hollow struc-ture showed superior electromagnetic wave absorption capacity and was responsible for matching the impedance of free space.The minimum reflection coefficients of hollow ZnO/nitrogen-doped carbon nanocomplexes were-51.2 dB(700℃)and-52.4 dB(800℃),respectively,whereas the effective ab-sorption band width was as large as 4 GHz and the content of pyrolyzed hollow ZIF-8 was 15 wt%,which was inferior to the level among similar electromagnetic wave(EMW)absorption materials.The conve-nient and facile strategy paves the way toward designing hierarchical structures for highly efficient and light-weight electromagnetic wave absorbers.

STUDY ON SIMILARITY LAWS OF A DISTORTED RIVER MODEL WITH A MOVABLE BED

WT5”BZ]In this study, by considering the scale ratio related to the specific gravity of the submerged bed material, and introducing a degree of distortion, n the similarity laws for a distorted river model with a movable bed were derived under the conditions that the values of dual dimensionless parameters in a regime-criterion diagram for the bars are the same in a model as they are in a prototype, and that a resistance law such as the Manning-Strickler-type formula is to be valid for a model and a prototype. The usefulness of the similarity laws derived in this study was verified by comparing the bed forms from the distroted model experiments with the bed forms from the 1/50-scale undistorted model experiments, which were performed by the Hokkaido Development Bureau (H. D. B.), Japan, to examine the tentative plan for the improvement of a low-flow channel in the Chubetsu River, which is a tributary of the Ishikari River. It is considered that the distorted model experiments to be valid with either sand or lightweight bed material. [WT5”HZ]