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Behavior of spacecraft structural materials under the high-velocity impact should be thoroughly investigated due to the constant threat of collision with space debris and meteoroids. Syntactic foams are perspective lightweight composite materials for spacecraft protection capable to attenuate shock waves. The shock response of highly filled syntactic foam to uniaxial planar impact loading was investigated using a powder gun facility and a laser velocimeter technique. The studied 0.64 g/cm3 foam consisted of an epoxy matrix filled with 55% volume fraction of glass microspheres. Measured wave profiles demonstrate the complex two-wave configuration associated with formation of precursor and compaction waves. Hugoniot and strain-rate data for the syntactic foam are presented in the stress range of 0.28–0.7 GPa. The Hugoniot elastic limit are determined to be 0.12 GPa, which implies that a precursor cannot be neglected in shocked state calculations in the studied loading regime. The density of the foam decreases with increasing loading stress due to thermal effects. The effect of sample thickness on wave fronts, wave velocities and precursor amplitudes is described. Precursor waves did not reach stable states in the experiments.

Is it possible to create low-cost functional composite metal foams? In the framework of this study, composite metal foams filled tubes were produced with lightweight expanded clay aggregate particles. Specimens were manufactured by low pressure infiltration in aluminium tubes with the wall thickness of 5 mm. The properties of the transition layer between the matrix material and the material of the tube were analysed with energy dispersive X-ray spectrometry. The importance of the research was to develop lightweight, high-capacity functional composite metal foams which have higher specific mechanical properties than ’conventional‘ metal foams, thereby achieving additional weight reduction and lower material requirements, primarily as moving machine parts or automotive components, while keeping overall costs low.

Silica fume, a by-product obtained during the smelting process of silicon and ferrosilicon alloys, is widely used as a filler material in concrete for construction purposes. This study discusses the use of silica fume (1–7% v/v) as novel fillers in epoxy glass microballoon syntactic foams. The total filler loading i.e. glass microballoons and silica fume is maintained at 40% (v/v). Epoxy syntactic foams are popularly being used in the construction industry for the fabrication of light-weight materials in the sandwiched configuration. The use of silica fume is expected to improve the mechanical properties of such syntactic foams, which otherwise suffer due to the incorporation of hollow glass microballoons. As expected, the incorporation of silica fume enhanced the mechanical properties of the base syntactic foam. Epoxy glass microballoons reinforced with silica fume (5% v/v) increased the specific tensile strength by ∼ 47 percent, flexural strength by ∼ 54 percent and compressive toughness by ∼ 23 percent, etc. The increase in properties is attributed to the homogenous dispersion of the silica fume throughout the matrix and the load-bearing ability of silica fume. The use of silica fume opens up vistas in the field of polymer syntactic foams.

In the ongoing development of light-weighted materials, syntactic foams have superior features over open-cell and closed-cell foams. Amongst the metal-based foams, syntactic foams have least material utilization and are fairly porous. Fly ash production is one of the major consequences of combustion of fossil fuels. The low density of fly ash, combined with robust properties of aluminium and magnesium can lead to the formation of light-weighted and high strength syntactic foams. This paper discusses preferable characteristics, advantageous effects and outcomes of the composite syntactic foams fabricated using fly ash as reinforcing material within the aluminium and magnesium matrices, on the basis of proceeding investigations carried out across the globe. By using fly ash as a reinforcement material, avoidance of challenges such as inhomogeneity, sudden deleterious reactions, change in alloy chemistry and reinforcement gradients is attained. Hence, syntactic foams with fly ash as reinforcement material finds wide applications in compressive and high temperature conditions. Effect of using fly ash in aluminium and magnesium syntactic foams, considering change in alloy matrix and dimensional changes of reinforcement on mechanical and thermal properties have been summarized. Already assessed and further possible applications have also been enlisted.

The purpose of innovative engineering inventions in our modern world is not necessarily to solve a new problem, but to implement and optimize an existing solution in a more energy-efficient and cost-effective manner. This can be achieved by increasing the load-bearing capacity or reducing the weight. Using these two methods simultaneously we can produce so-called syntactic metal foams. The mechanical properties of syntactic foams are highly dependent on the filler materials’ volume. Therefore, in the course of our research, we produce gradient syntactic metal foams (GSMFs) with gradient filler volume within one metal foam. Mechanical analysis as compressive tests and microstructural analysis were performed to determine the properties of the differently filled syntactic metal foams.

Owing to the expanding world of materials, there appears an intelligible and timely need for the development of materials that are easily fabricable, light in weight and have greatly enhanced properties in comparison with the conventional ones. A quick glance on foams, alluding a cellular closed structure, depicts remarkable combination of optimized material utilization for high strength and low density. Aluminium, being commonly available and light weighted, under controlled processing, offers substantial advantages for the evolution of improved materials. Aluminium Syntactic Foams (ASFs) are the composites having aluminium matrix with usually pre-formed inorganic hollow spherical reinforcements arranged in an orderly fashion with constituents of either metallic, polymeric or ceramic nature, or superfluous byproducts. These spherical reinforcements impart high strength to the syntactic foams and compensate the lower hardness and stiffness of aluminium. Several researches have been done for developing lightweight materials. Liquid route has proven highly effective over the solid-state methods for fabrication of lightweight materials. Dispersion mechanisms are adopted by various liquid route fabrication methods offering uniform distribution of reinforcements within the aluminium matrix. With focus on Aluminium Syntactic Foams (ASFs), these fabrication methods are broadly classified in the current study and, their constructive effects on properties are a summarized and scrutinized on the basis of ongoing explorations being conducted across the world.

This research focuses on the mechanical investigations of in-situ produced AlSi12 aluminium alloy matrix syntactic foam-filled tubes. The samples were manufactured by low-pressure infiltration in a tube made from AlMgSi0.5. As second phase 3.5–4 mm average diameter lightweight expanded clay aggregate particles were used. The mechanical analysis extends to compressive tests of three different type of samples: empty tubes, metal matrix syntactic foams, and foam-filled tubes. The results show the best specific mechanical energy absorbing capacity in the case of foam-filled tubes, since the matrix creates a durable boundary layer with the tube wall.

In this paper, experimental study on drilling of cenosphere reinforced epoxy composites was carried out to investigate drilling characteristic using tungsten carbide drill bits. The influence of drilling process variables, such as feed rate, drill diameter, % weight of reinforcement and spindle speed on Specific Cutting Coefficient (SCC) has been studied. The composite samples were prepared with varying concentration of cenosphere (filler) by varying the content from 10% to 60% in 25% increment in the epoxy resin matrix. The plan for the drilling experiments was based on full factorial design (FFD). The drilling characteristic was analyzed through mathematical equation based on Response Surface Methodology (RSM). The experimental investigation on drilling characteristic clearly revealed that the SCC decreases with an increase in the feed rate and % of fly ash cenosphere in epoxy resin matrix.

This paper analyses prediction methods for failure pressure of microspheres in the structure of syntactic foams, discussing several micromechanical models. The solutions were obtained as per linear elasticity theory and finite-element method. It was investigated how geometric and physical & mechanical characteristic of syntactic foams depend on its components. Pressure failure is much lower if the boundary of the medium is close to the inclusions. This paper suggests an analytical model that yielded conservative estimate of critical pressure for microspheres.

Bu çalışmada köpük metallerin geliştirilmiş bir şekli olan Sintaktik Köpük Metal (SKM) üretilmiş ve analiz edilmiştir. SKM’de yapı içindeki gözeneklilik, içi boş seramik küreler yardımıyla oluşturulmaktadır. SKM kapalı hücre yapısına sahiptir. SKM’lerin avantajları; hafiflik, yüksek basma dayanımı, titreşim sönümleme ve enerji absorbe etme kabiliyetidir. Kompozit bir malzeme olan SKM’in üretiminde matris malzemesi olarak 7075 alüminyum, takviye malzemesi olarak da içi gözenekli yapıya sahip genleştirilmiş cam küre kullanılmıştır. Çalışmamızda SKM sıvı infiltrasyon yöntemi ile üretilmiştir. Bu üretim yönteminde kalıp ve küreler, 800 ˚C sıcaklıktaki fırında bekletildikten sonra fırından çıkarılmış ve kalıp boşluğuna cam küre ve ergimiş alüminyumun yerleştirilmesinden sonra 6,3 kPa’lık döküm basıncı uygulanmıştır. Üretilmiş olan SKM’lerin içyapısı analiz edilmiş, cam kürelerin yapı içinde homojen bir şekilde dağıldığı ve kürelerin kırılmadığı tespit edilmiştir. 25 mm çapında ve 30-33 mm yüksekliğe sahip silindirik SKM numunelerin yoğunluk değerleri Arşimed prensibi kullanılarak 1,33-1,68 g/cm3 olarak ölçülmüştür. Gözeneklilik değerleri ise %53,3-57,2 olarak hesaplanmıştır. Mekanik testler için basma deneyleri gerçekleştirilmiş ve SKM’lerde görülen tipik plato eğrileri tespit edilmiştir. Plato dayanım değerleri 22-42 MPa, darbe sönümleme enerji değerlerinin ise 12-22 MJ/m3 arasında olduğu görülmüştür. Bu değerler literatürde karşılaşılan verilerle uyumlu olduğu ve plato dayanım değeri ile enerji absorbe etme değerleri arasında doğrusal bir ilişkinin var olduğu tespit edilmiştir.

The incorporation of multi-walled carbon nanotubes (MWCNTs) into syntactic foams (hollow glass microspheres bonded to a polymer matrix) can enhance the mechanical performance of syntactic foams. In this study, several syntactic foam specimens reinforced with MWCNTs were manufactured and tested under static and low-velocity impact loads, and the mechanical properties of these syntactic foams were compared to those of reference syntactic foams without MWCNTs by focusing on the impact resistance and optimal energy absorption. Moreover, the influences of the applied impact energy and microsphere and MWCNT contents on the impact responses of syntactic foam panels were discussed, and the vibration equation of a panel with four clamped edges was determined based on the energy principle. An analytical solution for the displacement responses of the syntactic foam panels under sinusoidal impact loads is proposed, in which Young’s modulus of the syntactic foam is expressed as a function of the moduli of the fillers and binders and contents of the fillers. The predicted maximal displacements agree with the experimental values well.

Epoxy syntactic foam (ESF) materials are widely used in marine detection systems, deep sea diving equipment, offshore oil exploration and other deep sea development and exploration equipment due to their superior properties such as low density, high compressive strength and low water absorption. The composition and preparation process of the ESF material determine the structure of the ESF material, the structure determines the performance, and the performance determines the application of the ESF material. The review describes the epoxy-based syntactic foams from the following aspects: definition and classification, preparation methods, properties and influencing factors, application, problems and development trend. The forming methods of hollow glass microspheres (solid-state powder processing method and liquid atomization method), hollow polymer microspheres (spray drying method) and centimeter-sized hollow spheres (rolling ball method and electrostatic fiber flocking method) are introduced in detail, as well as the casting molding method, vacuum molding method and pressure molding method of the syntactic foams. The main objective of this paper is focusing on the influence of various factors including filler content, graded structure, clay material, carbon material, fiber-reinforced material, molding process, material structure (sandwich structure) on the compressive strength and the density of the syntactic foam in detail. The paper may also provide some guidance to the preparation of ESF used in deep sea development and exploration equipment.

In this study bimodal A413 matrix syntactic foams filled with ceramic hollow spheres (CHSs) were produced and examined by computer tomography (CT) and quasi-static mechanical testing to determine the mixing properties of the hollow spheres and the strength of the metal foam. Two hollow spheres of different nominal diameters (d1 = 2.4 mm and d2 = 7.0 mm) were used in equal volume ratio. The produced metal foams have a density of 1.61±0.03 g/cm3, with smaller inclusions and some defective hollow spheres in the structure. The foams have an average compressive strength of 120 MPa and a specific mechanical energy absorbing capacity of 43.5 J/cm3. As a result of the upsetting tests, the matrix material is separated from the CHSs, breaking the connection between them.

In recent years, there has been an increasing interest in the study of lightweight syntactic foams (SFs) because of their tailorable properties, quality characteristics and suitable applications in diverse technology industry. A considerable amount of literature has been published on SFs with most of these studies focusing on particular aspect like the matrices types (polymer, metal, ceramics, bio and hybrids); filler types (microparticles/microballoons/microspheres); nanoadditives types (nanotubes, nanofibers, nanoparticles); types of production techniques (powder metallurgy, infiltration and casting, mechanical molding and chemical deposition); and industry applications (aerospace, marine, building and construction, automotive and electrical and electronics). However, much of the literatures up to now has been research articles and few review articles. And there has been no attempt to comprehensively discuss SFs touching on the main research interest in a robust manner. Thus far, this study, brings a comprehensive insight toward the isolated research areas in SFs and then, compares and summarizes outcomes and inference from previous and current studies. And recommends on future research.

Sandwich composites with polymeric open-celled foams or honeycomb structures as core materials have been used widely in low-weight naval, aerospace and structural applications in the past. One majo...

Epoxy resin is one of the commonly used matrixes of syntactic foams as a buoyancy material, the curing agents of which affect some of the properties for syntactic foams. Therefore, the curing reactions of N,N,N',N'-tetraepoxypropyl-4,4'-diaminodiphenylmethane (AG-80) epoxy resin between 4,4-diaminodiphenyl methane (DDM) and the mixture of m-xylylenediamine and DDM (DDM-m-XDA) systems are studied. The DDM mixed with m-XDA enhances curing reactions with the AG-80 epoxy resin, and the mechanisms of the two curing systems are different through nonisothermal kinetics. Compared with a single curing system, there are some wrinkles on the surface of the AG-80/DDM-m-XDA matrix because of the disordered network. Composited with hollow glass microspheres (HGMs), the more flexible m-XDA structure enhances the interfacial adhesion between the matrix and HGM for syntactic foams. However, the wrinkles in the matrix increase the broken degree of HGMs; especially at HGM contents higher than 55%, the flaw increases the density and water absorption of syntactic foams; meanwhile, it decreases the compressive strength. Therefore, the properties of syntactic foams can be improved by mixing different molecular structure curing agents and the mixture liquid curing agent simplifies the preparation process to some extent.

The goal of this paper is to enable three-dimensional (3D) printed lightweight composite foams by blending hollow glass microballoons (GMBs) with high density polyethylene (HDPE). To that end, lightweight feedstock for printing syntactic foam composites is developed. The blend for this is prepared by varying the GMB content (20, 40, and 60 volume %) in HDPE for filament extrusion, which is subsequently used for 3D printing. The rheological properties and the melt flow index (MFI) of blends are investigated for identifying suitable printing parameters. It is observed that the storage and loss modulus, as well as complex viscosity, increase with increasing GMB content, whereas MFI decreases. Further, the coefficient of thermal expansion of HDPE and foam filaments decreases with increasing GMB content, thereby lowering the thermal stresses in prints, which promotes the reduction in warpage. The mechanical properties of filaments are determined by subjecting them to tensile tests, whereas 3D printed samples are tested under tensile and flexure tests. The tensile modulus of the filament increases with increasing GMB content (8-47%) as compared to HDPE and exhibit comparable filament strength. 3D printed foams show a higher specific tensile and flexural modulus as compared to neat HDPE, making them suitable candidate materials for weight-sensitive applications. HDPE having 60% by volume GMB exhibited the highest modulus and is 48.02% higher than the printed HDPE. Finally, the property map reveals a higher modulus and comparable strength against injection- and compression-molded foams. Printed foam registered 1.8 times higher modulus than the molded samples. Hence, 3D printed foams have the potential for replacing components processed through conventional manufacturing processes that have limitations on geometrically complex designs, lead time, and associated costs.

In this study a FE model is prepared for drop weight impact hammer testing of polymeric syntactic foam. The foam is modelled using crushable foam material and hammer is modelled using bilinear material model of LS-DYNA®. A series of simulation is performed by varying density of foam and impact velocity of hammer. Based on the prepared FE model and the force-displacement relation, energy absorption of the foam is computed and compared for three densities and three velocities. A comparative study is presented based on the displacement, reaction force-time history, and forcedisplacement behaviour.

A method for the reuse of aluminum (alloy 5754) sawing chips as a starting material for manufacturing aluminum matrix syntactic foams by powder metallurgy is described. In the tested samples, spherical Ni-superalloy hollow particles were used to increase the closed porosity of specimens up to 50 wt.%. Spark plasma sintering was used to consolidate the specimens. Only the sample with 30% hollow particles showed a clear maximum corresponding to a compression strength of 130 MPa. For all the samples, the plateau stress was over 120 MPa. The densification strain was over 40%, reaching 61% for the sample containing 30% hollow particles. All the samples showed high energy absorption capabilities and good absorption efficiency.

Syntactic foams are composite materials consisting in the association of hollow particles, called “microspheres” and a polymer matrix. The use of soft shell microspheres confers to the foam interesting properties but in return increases significantly its compressibility. Therefore, understanding and predicting the relationship between pressure and volume change is a crucial issue for the development of this type of material. The present study focuses on a high void fraction syntactic foam made with soft shell polymer microspheres embedded in a polyurethane matrix. Compression tests are performed using a capillary rheometer and a PVT accessory for the hydrostatic compression, and a more conventional apparatus for the confined compression. The experimental results are compared with De Pascalis’s pressure/volume model predictions, using Fok and Allwright’s model to determine the critical buckling pressure of the microspheres. The model proves to be fairly accurate at low pressure and high pressure, despite a notable deviation in the mid-pressure range. The influence of key model parameters such as microsphere size distribution and microsphere and matrix elastic properties is investigated. It is shown that the reinforcement of the matrix seems to be the only efficient way to limit the compressibility of such a syntactic foam.

Physicomechanical, thermophysical, and electrical properties of syntactic foams based on ED-20 epoxy diane resin and hollow phenol-formaldehyde microspheres have been considered. The optimal amount of microspheres in the composition has been determined. It has been shown that hollow microspheres affect the adhesion and strength characteristics of the sealant and reduce the dielectric loss tangent in the centimeter UHF range, which allows one to recommend such syntactic foams as sealing compositions in radioelectronic equipment and antenna-feeder devices operating in the ultra-high-frequency radio range.

Glass microballoons (GMBs) are commonly used to reduce the density of epoxy-resin syntactic foams, but they can also be applied as a low-cost and lightweight catalyst support. In order to create a practical structure that can be utilized for such an application, a ceramic syntactic foam consisting of glass microballoons (GMBs) and silica nanofibers (NFs) with or without TiO2 binder was synthesized. The mechanical strength, phase composition, high-temperature deformation behavior, and microstructure of the composite material were analyzed using bending and compression tests, X-ray diffraction, and scanning electron microscopy, respectively. It was determined that the addition of nanofibers improves the thermal behavior and mechanical strength of the composite material during and after processing. The composite materials maintained up to 70% anatase titania at as high as 700 °C, and this indicates that they can be of interest for high-temperature catalysis. No high-temperature deformation of GMBs was observed at 800 °C or 1000 °C, whereas XRD of samples coated with TiO2 using a titanium oxysulfate solution indicated the formation of cristobalite above 800 °C. Preliminary methane-reforming experiments were performed with NiO-seeded titania-coated GMBs, uncoated GMBs, and an uncoated silica fibers/GMBs composite. Uncoated GMBs and titania-coated GMBs had a low conversion ratio of methane to products, but the uncoated composite structure showed high conversion of the reactants at high temperatures, indicating that it may be suitable catalyst support in this reaction.

Short carbon fiber (CF), epoxy-hardener (EP-hardener), and expanded polystyrene (EPS) beads were used to prepare CF-reinforced hollow epoxy macrospheres (CFR-HEMS) by the “rolling ball method”. The multiphase epoxy syntactic foam (ESF) was prepared with CFR-HEMS, the EP-hardener system, and hollow glass microspheres (HGMS) by the “compression modeling method”. In this experiment, the influences of the stacking volume fraction, wall thickness, and inner diameter of the CFR-HEMS and HGMS types and contents in the EP-hardener system on the properties of the ESF were studied. In addition, CFs with different meshes were used to reinforce hollow epoxy macrospheres (HEMS) to study the effect of different kinds of CFs on the compressive strength of the ESF. During the mixing of the EP-hardener and HGMS (EP-hardener–HGMS), 300 AW CFs with different contents were added to the system to enhance the compressive strength of the ESF. The CFR-HEMS spherical wall was combined tightly with the EP-hardener–HGMS system by a scanning electron microscope (SEM). The ESF, which has better properties relatively in the experiment, can be used in 2673 m deep water and provide 490 kg/m3 buoyancy, which can be of help in the preparation of buoyancy materials in detection systems and oil extraction systems in the deep sea.

Polymeric foam core sandwich composites are the nascent materials used in marine and aerospace structural applications for its low-density characteristics. A special class of foam called syntactic foam is one of the promising core material having high specific properties. However, these polymeric foam core sandwich composite structures may encounter problems in correlation with temperature and fire. Damages that happen due to the variation in temperature and by the catch of fire are sometimes imperceptible which may lead to the deterioration of load carrying ability or catastrophic failure of these composite structures. Present investigation is focused on the possibilities of reducing the extent of damages due to variation in temperature and by the catch of fire by enhancing its thermal stability and flame resistance characteristics. This was achieved from the development of syntactic foam by embedding hollow micro-spherical particles in phenolic resin for fire containment or fire isolation. Result of the experimentation reveals that the phenolic syntactic foam core was thermally more stable than glass/epoxy face skins up to a temperature of 450°C. The minimum concentration of oxygen required for burning was found to be 30%, in which phenolic syntactic foam core helps in flame isolation, whereas E-glass/epoxy face skins contribute to flame spread in the event of burning of sandwich composites. Improved thermal stability and fire resistance characteristics of developed sandwich composites are attributed to the phenolic syntactic foam core and by its orientation.

Alumina hollow spheres with a diameter range of 1–2 mm were filled in 6061 Al alloy by gravity infiltration casting to synthesize Al-matrix syntactic foams. The effects of infiltration temperature and heat treatment on microstructure, compressive properties, and energy absorption properties of the syntactic foams were studied. The results show that high quality syntactic foams could be synthesized in the infiltration temperature range 770–830 °C and the particles seamlessly bonded with the matrix. The average density and porosity of the syntactic foams were around 1.66 g/cm3 and 37.47%, respectively. The highest energy absorption capacity and specific energy absorption of the as-cast syntactic foams occurred at infiltration temperature 770 °C, reaching 41.11 MJ/m3 and 23.63 kJ/kg, respectively, while these parameters for the heat-treated samples showed the maximum values for the solution-aging treated samples, reaching 48.92 MJ/m3 and 31.36 kJ/kg respectively. Extensive literature survey is presented in this work by extracting the compressive properties of a variety of Al-matrix syntactic foams and comparing them with the results obtained in the present work. It is observed that the syntactic foams synthesized by gravity infiltration method equal or exceed the properties demonstrated by many Al-matrix syntactic foams synthesized by other methods reported in recent years. As a major advantage, the gravity infiltration method can be scaled up to industrial production level.