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A syntactic foam was prepared from an epoxy resin matrix and modified hollow glass microsphere fillers. Modification by silane coupling agents with different molecular structures was analyzed, and the optimal content of the silane coupling agent was determined. The results demonstrated that all silane coupling agents enhanced the adhesion between the hollow glass microspheres and epoxy resin matrix, resulting in enhanced water absorption, compressive performance, tensile performance, and bending performance compared to those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end groups, the one with a sulfhydryl end group exhibited optimal modification for hollow glass microspheres. Among the silane coupling agents with different backbone structures, the one with silanol groups exhibited the optimal modification of hollow glass microspheres. Additionally, the performance of the syntactic foams was optimal when 6% of the silanol-containing coupling agent was used. The results demonstrated that syntactic foams prepared with hollow glass microspheres modified by silane coupling agents exhibited improvements in water absorption, compressive performance, tensile performance, and bending performance, compared with those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end structures, the one with a sulfhydryl group as end group showed the best modification effect on hollow glass microspheres. The water absorption was 0.35%, the compressive strength was 62.15 MPa, the tensile strength was 40.15 MPa, and the bending strength was 53.17 MPa. Among silane coupling agents with different backbone structures, the one with silanol groupsbonds showed the best results. Its compressive strength was up to 64.15 MPa, the tensile strength was 35.47 MPa, and the bending strength was 53.99 MPa.

This research study introduces a novel functionally graded metal syntactic foam. Counter-gravity infiltration casting is employed to manufacture MSF layers with dissimilar metallic matrices. Each layer combines expanded perlite particles with a different matrix alloy, i.e., ZA27 or pure aluminum. Dissimilar MSF layers are combined either during casting or using different joining techniques following manufacturing. The dissimilar matrices introduce a controlled gradient of the physical and mechanical properties of the resulting functionally graded foam material. Quasi-static compression testing shows that the initial deformation is controlled by the weaker aluminum syntactic foam layer. Following partial densification of this layer, deformation transitions toward the layer containing the higher strength ZA27 matrix alloy.

The objective of this work is to improve the structural characteristics of hollow glass microsphere (HGM) filled epoxy syntactic foam composites with little voids content and improved HGM dispersion in the composite. A modified degassing technique has been introduced during resin casting process of the HGM filled syntactic foam composites. The effect of HGM content volume fractions (5–25%) on the degassing techniques was examined. The syntactic foam composites were characterized by analysing structural morphology using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy(TEM), and density measurements (theoretical and experimental). Less than 5% void content has been achieved in this study. This resulted in improved tensile and dynamic mechanical properties (DMA).

In this paper, we report the effect of introducing molybdenum disulfide (MoS2) nano-platelets: a two-dimensional metal chalcogenide, on the mechanical properties of hollow glass microballoon (HGM)–epoxy syntactic foams. MoS2 reinforced syntactic foams were prepared by mixing MoS2 nanoplatelets to epoxy containing HGMs; with the amount of MoS2 being varied from 0.01 to 0.04% v/v, while maintaining a constant total filler volume fraction of 40% for all compositions. The mechanical behaviour of reinforced syntactic foam was studied under varied loadings including compressive, tensile and flexural under different strain rate regimes. Introduction of MoS2 led to significant improvements in characteristic mechanical properties, particularly in terms of compressive strength and toughness, which suggest intercalation of MoS2 within the epoxy matrix; however, the presence of relatively larger MoS2 micro particles couldn’t be completely negated. The toughness of the foam, as indicated by the area under the compressive stress-strain curve, was found to increase by ∼21% under optimal conditions. Our results highlight the potential of the two-dimensional MoS2 sheets as a reinforcing agent in syntactic foams.

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.

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.

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.

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.

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.

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.

Hollow glass microsphere-reinforced epoxy hollow spheres (HGMS–EHSs) were prepared by a “rolling ball method” using expanded polystyrene beads, HGMSs, and epoxy resin (EP). The three-phase epoxy syntactic foam (epoxy/HGMS–EHS–HGMS composite) was fabricated by combining HGMS–EHS as a lightweight filler with EP and HGMS by a “molding method”. The HGMS–EHS and epoxy curing agent systems were well mixed by scanning electron microscopy. Experiments show that higher HGMS–EHS stack volume fraction, lower HGMS–EHS layer number, higher HGMS–EHS diameter, lower HGMS–EHS density, higher HGMS volume fraction, and lower HGMS density result in a decrease in the density of the three-phase epoxy syntactic foam. However, the above factors have the opposite effect on the compressive strength of the three-phase epoxy syntactic foam. Therefore, in order to obtain the “high-strength and low-density” three-phase epoxy syntactic foam, the influence of various factors should be considered comprehensively to achieve the best balance of compressive strength and density of the three-phase epoxy syntactic foam. This can provide some advice for the preparation of buoyancy materials for deep sea operations.

Syntactic foams are synthesized by using pre-fabricated hollow microspheres. Syntactic foams are used as energy absorption sandwich core for several applications like marine, automotive and aerospace. Properties of syntactic foam can be tailored by addition of filler material. In this work hybrid syntactic foam is fabricated by addition of two types of filler materials that are hollow glass microballoons and fly ash cenosphere into vinyl ester matrix at different concentration. The volume fraction of filler content with respect to matrix is fixed to 50% and composition of two fillers varied. Hybridization of two different types of ceramic microballoons in vinyl ester matrix gives maximum 9.58% improvement in impact strength with respect to plane hollow glass microsphere syntactic foam. Enhancement in flexural strength and Flexural modulus observed is 27.7% and 27.16% respectively as compared to plane hollow glass microsphere syntactic foam

In the present study, the tribological behaviour of the syntactic foams manufactured using the fly ash cenospheres as the reinforcements and the epoxy as the matrix were studied for their tribological performance. The effect of the reinforcement concentration on the tribological properties like wear rate and the coefficient of friction were observed by using the pin on disc tribo tester. Four types of samples were prepared by varying the cenosphere volume fraction from 10% to 40% and tribological tests were conducted at constant sliding speed of 1 m/s and constant applied load of 50 N for a sliding distance of 2000 m. The increase in cenosphere volume fraction reduced wear rate and increased friction coefficient. The reduction in the wear rate may be due to the reduction in the effective contact area due to the pores created by crushed cenospheres. The increment in the coefficient of friction may be due to the increase in the cenosphere shells in the wear debris which act as obstacles. The worn surfaces of the foams were observed using the scanning electron microscope to determine the dominant wear mechanism.

Products made of syntactic foams are replacing many conventional materials due to several desirable properties and commendable low density. To overcome its limitation in application it has been hybridized with CNT in this work to achieve multifunctional, mechanical and thermo-mechanical enhanced composites. It is found that when HGM is added to epoxy/CNT matrix compressive strength increases till 5% to a maximum value of 176MPa at 5wt% of HGM and beyond this volume of HGM strength decreases considerably. Storage modulus increases with increase in HGM volume due to increased restriction in polymer chain mobility of epoxy matrix. Microstructure images of fractured surface of the composites evident the good dispersion of HGM and CNT in the epoxy matrix. It can also be seen in SEM images that many microcracks generated are discontinuous and hence increasing the stability of composite in plastic region

Epoxy/hollow glass microsphere (HGM) syntactic foams (SFs) are peculiar materials developed to combine low density, low thermal conductivity, and elevated mechanical properties. In this work, multifunctional SFs endowed with both structural and thermal management properties were produced for the first time, by combining an epoxy matrix with HGM and a microencapsulated phase change material (PCM) having a melting temperature of 43 °C. Systems with a total filler content (HGM + PCM) up to 40 vol% were prepared and characterized from the mechanical point of view with a broad experimental campaign comprising quasi-static, impact, and fracture toughness tests. The experimental results were statistically treated and fitted with a linear model, to produce ternary phase diagrams to provide a comprehensive interpretation of the mechanical behaviour of the prepared foams. In quasi-static tests, HGM introduction helps to retain the specific tensile elastic modulus and to increase the specific compressive modulus. The brittle nature of HGMs decreases the Charpy impact properties of the SFs, while the PCM insertion improve their toughness. This result is confirmed in KIC and GIC tests, where the composition with 20 vol% of PCM shows an increase of 80% and 370% in KIC and GIC in to neat epoxy, respectively. The most promising compositions are those combining PCM and HGMs with a total particle volume fraction up to 40 vol%, thanks to their optimal combination of thermal management capability, lightness, thermal insulation, and mechanical properties. The ability to fine-tune the properties of the SFs, together with the acquired thermal energy storage (TES) capability, confirm the great potential of these multifunctional materials in automotive, electronics, and aerospace industries.

In the present study, the thermal behavior of pure Al6061 and fly ash reinforced Al6061 with varying particulate sizes were investigated for the first time. Metal matrix syntactic foams of ceramic fly ash (4 – 16 wt. %) embedded in aluminum (Al6061) matrix have been fabricated by using stir casting technique with different fly ash particulate sizes of size below 50µm and 53µm-100µm, respectively. The microstructural characteristics were studied by using scanning electron microscopy (SEM). It has been observed that there is a uniform distribution of lower particulate size fly ash as compared to higher particulate size in the aluminium matrix respectively. For all the cases, the accumulation of fly ash in Al6061 decreases the thermal conductivity and increases the specific heat carrying capacity of a hybrid composite. Increase in weight percentage of fly ash in Al6061 decreases thermal conductivity and thermal diffusivity respectively.

In this article, the co-continuous hollow glass microspheres (HGMs)/epoxy resin syntactic foams were prepared by filling the HGM preforms with epoxy resin. The effects of HGM wall thickness and solid loading on the density, open porosity, and morphology of HGM preform and HGM/epoxy resin syntactic foams were studied in detail. The results show that the HGM wall thickness had no effect on the open porosity of HGM preforms. However, the density of preforms increased with the true density of HGMs. The density of HGM/epoxy resin syntactic foams decreased with the contents of HGMs, and the measured density was essentially equal to the theoretical density. The compressive strength decreased with the contents of HGM, regardless of the HGMs wall thickness. However, the variation in compressive modulus was related to the HGMs’ wall thickness. As the HGM solid loading increased, the compressive modulus of composites, prepared using thin-walled HGMs, decreased, while the composites prepared using thick-walled HGMs showed the opposite trend. The co-continuous HGM/epoxy resin syntactic foams possessed low density (0.567–1.002 g/cm3), and excellent compressive strengths (30.32–131.60 MPa). These properties were due to the elimination of matrix pores, and are a type of promising material in deep sea exploration area.

Conventional mould casting technique for cell foam production demonstrated trapped air bubbles in the cell foam which are undesirable stress concentration points in the matrix. This study devise a modified process technique of fabricating syntactic foam by eliminating interstitial porosity. Varying epoxy hollow spheres and matrix stoichiometry ratio was involved in the fabrication of syntactic foam. Analysis through characterization of the mechanical properties, macrostructural morphology, cell size distribution, wall thickness and curing conditions was determined. The influence of fabrication techniques on performance of the syntactic foams was also evaluated. From the results the hollow sphere size distribution prevented the interstitial spaces, enhanced density and create foam compactness. The matrix stoichiometry ratios impacts the foam morphology, the optimal formulation was 1:1 because it enhances cross-linking within the matrix and produced a smooth, strong surface microsphere coating with structural rigidity. The relative density, compressive modulus and compressive strength of the syntactic foam are 377.11 kg/m3, 556.39 MPa, 10.40 MPa and 334.61 kg/m3, 37.05 MPa, 4.11 MPa, for vacuum assisted mould filling and conventional mould casting method, respectively. Crack propagation test showed failure started at the center and spread through the edges of the syntactic foam because of good interfacial bonding between sphere and matrixes. Keywords: Syntactic foam, Microsphere, Mechanical properties, Vacuum assisted mould technique

It is generally accepted that matrix pores in the hollow glass microspheres (HGMs)/resin-based composites prepared using stir-casting method (SCM) seriously affect its performance. In this paper, H...

This paper investigates the effect of temperature on the microstructure, failure mechanism and compressive mechanical properties of newly developed ZA27 syntactic foams. Two different types of filler particles are considered, i.e. expanded perlite (P) and expanded glass (G). Metallic syntactic foam (MSF) has been produced via a counter-gravity infiltration process of packed particle beds, followed by controlled thermal exposure. Quasi-static compressive tests were carried out on cylindrical samples at five different in-situ testing temperatures between 25 °C and 350 °C. At all considered temperatures, P-MSF exhibits superior mechanical properties compared to G-MSF. The mechanical properties of both foam types decrease significantly with increasing testing temperature. For comparison, solid ZA27 samples were compressed at the same testing temperatures. Due to microstructural changes, a significant strength degradation of solid ZA27 was observed starting at 100 °C. Comparison of results indicates that the temperature-dependent mechanical properties of P-MSF and G-MSF are strongly controlled by the matrix material. However, the addition of particles decreased the relative reduction of plateau stress and volumetric energy absorption of ZA27 MSF at elevated temperatures.

The aim of this study was to research the effect of carbon nanofiber (CNF), the microballoon (MB) volume fraction and its density on both the vibration properties and impact behavior of carbon nano...

Quasi static compression (10−1, 10−2 and 10−3 s−1 strain rates) and dynamic mechanical analysis (temperature sweep of 30–175 °C) of cenosphere/epoxy syntactic foams are investigated. Effect of cenosphere content (20, 40 and 60 vol %) and surface modification are presented. Quasi-static tests reveal lower modulus for neat epoxy samples as compared to all the syntactic foams. With increasing cenosphere content and strain rate, elastic modulus increases for all the tested conditions. Foams reinforced with surface modified cenosphere exhibit higher modulus as compared with untreated ones and neat epoxy. Energy absorption of samples increases with increasing cenosphere content and surface modification. Storage modulus of untreated and treated syntactic foams register higher values with increase in cenosphere content and are higher than the neat epoxy samples. Loss modulus of syntactic foams at room temperature are lower as compared with pure epoxy while damping of untreated and treated foams registered higher values as compared with neat resin. Scanning electron microscopy of the samples are performed for structure property correlations. Finally, property map for quasi-static compression is presented by comparing results of present work with the extracted values from literature.

Carbon nanofibers (CNFs) and halloysite nanotubes (HNTs) were incorporated in syntactic foams containing a 90% by volume homogeneous mixture of (20/80 wt%) glass/thermoplastic microballoons to enhance the mechanical and impact response properties. Tensile, compressive, and impact tests were employed to comparatively characterize the effect of nano-additive reinforcement on mechanical response properties. Compressive strength and modulus enhancements as large as 39% and 18%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 61% and 7%, respectively, were achieved with a 0.125 wt% addition of HNT. Tensile strength and modulus enhancements as large as 107% and 68%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 104% and 70%, respectively, were achieved with a 0.125 wt% addition of HNT. Impact analysis data were used to show that measured peak force increased and build-up time to peak force decreased with increasing CNF or HNT weight percentage due to stiffening of the matrix. The smallest increase observed in peak force was 20% for a 0.125 wt% addition of CNF and 17% for a 0.125 wt% addition of HNT.

The production of low-temperature clay lightweight aggregates is pursued eagerly as low energy and cost lightweight aggregate concrete (LAC) building blocks becomes more popular. Clay ceramic hollow spheres (CCHS) with waste glass (WG) additive was developed and studied as aggregate in cement composite. CCHS with diameter ranging in 6/8mm were produced by a sacrificial template technique with subsequent sintering under temperature of 900 °C and different WG content of 0, 5, 7 and 10 wt%. The effect of the sintering temperature and WG content on the physical properties and morphology of the CHS-cement composites were studied by means of optical microscopy and mechanical properties. Obtained composite materials were compared with commercially available lightweight fillers such as foamed glass granules and lightweight expanded clay aggregates (LECA). The results compressive strength of CCHS containing LAC is much higher from 4.8 to 7.1 MPa in comparison with the LECA-cement LAC - 3.5 MPa. Reduction of CCHS open porosity due to higher content of WG (10%) leads to lower absorption of cement paste, as result lower cement consumption, lower bulk density and compression strength. LAC with CCHS proved to be promising construction material due to low-temperature production process (i), widely available raw material (clay) and secondary material (glass cullet) use (ii), reduction of cement paste needed for material production (iii).

Epoxy syntactic foams with different compositions of cenosphere were fabricated and characterised. The effect of loading cenosphere in epoxy syntactic foams was analysed. Good thermal stability of cenosphere–epoxy syntactic foams was established from the thermogravimetric analysis results. The completion of cure reaction at ambient temperature conditions was ascertained from differential scanning calorimetry results. Dynamic mechanical analysis revealed 114°C as the glass transition temperatures ( Tg) for neat epoxy sample, which increased to 132°C with 50% loading of cenosphere. Cenosphere-filled epoxy syntactic foams had low density and low water absorption values when compared to the neat epoxy sample. Homogeneous distribution of the cenosphere particles was confirmed using scanning electron microscopy. The compression studies confirmed brittle failure of the syntactic foams. This was also supported by the scanning electron microscopic images. The incorporation of hollow cenosphere particles led to a decrease in the flexural strength. Syntactic foams with 30% loading of cenosphere exhibited best specific modulus and specific strength. The specific strength increased by 24% for T30 sample and specific modulus increased by 36% for T30 samples when compared to the neat epoxy sample. As the need for strong but lightweight thermally stable products is continually increasing, there is a great possibility for the utilisation of these cenosphere–epoxy syntactic foams as lightweight core for sandwich composites.

Effect of glass microballoon (GMB) wall thickness and cutting parameters (cutting speed, feed and drill diameter) on thrust force (Ft), surface roughness (Ra), specific cutting coefficient (Kf), cylindricity (CYL ), circularity error ( Ce-Exit) and damage factor (Fd-Exit ) in drilling of GMB/epoxy syntactic foam is presented. CNC vertical machining centre is utilised for conducting experiments based on full factorial design . Significant process parameters are identified through response surface methodology . Wall thickness significantly affects the Ce-Exit and CYL of the drilled hole. Increasing wall thickness significantly reduces the Ra (30%), CYL (41%) and Ce-Exit (56%) due to the increased thermal stability of syntactic foams. This observation is very crucial for the syntactic foams used in structural applications pertaining to structural stability. Drill diameter is observed to be significant for Ft, Ra, CYL and Fd-Exit; while Kf is governed by feed. Furthermore, grey relation analysis (GRA) is used to identify the specific combination of process parameters to obtain good quality drilled hole. Combination of higher particle wall thickness and feed, lower cutting speed and drill diameter produces a sound hole quality as observed from GRA. Hole quality is highly influenced by drill diameter followed by cutting speed and GMB wall thickness. The present study offers guidelines for the industries (structural applications) to produce quality holes in GMB reinforced epoxy matrix .

In this study, the flame-resistant epoxy syntactic foams with different content of hollow glass microspheres (HGM) were prepared by using aluminum diisobutylphosphinate (AlPBu) as flame retardant. Scanning electron microscope (SEM) images of the fracture surface of different epoxy syntactic foams showed that AlPBu particles had good compatibility with the matrix due to their similar polarities. And the limiting oxygen index, UL 94 test, cone calorimeter and thermogravimetric analysis were applied to characterize the flame retardation and thermal behavior of the foams. These results showed that AlPBu improved the flame retardancy of epoxy syntactic foams, while the HGM exhibit a complicated influence on the flame retardation, although both AlPBu and HGM enhanced the char residues and decreased the peak heat release rate as well as the total heat release of composites. In addition, swollen char layers mainly containing the HGM were generated after adding AlPBu. Then, the char residues of the foams after combustion were observed by SEM, and the results were applied to reveal the different fire behaviors of foams with different densities.

Al99.5 and AlSi12 matrix syntactic foams were produced by pressure infiltration of Globocer grade ceramic hollow spheres. The produced aluminium matrix syntactic foams (AMSFs) were investigated by compressive tests, dynamic mechanical analysis (DMA), finite element methods (DMA) and elasticity based analytical calculations. The aim of the investigations was (i) to map the compressive properties of the AMSFs, (ii) to determine and compare the effective Young's modulus of the AMSFs determined by compressive tests, DMA, FEM and analytical calculations and (iii) to determine the low frequency damping capability of the AMSFs. The compressive tests showed pronounced differences between the two matrix materials, characterized by higher compressive strength, compressive strain and absorbed mechanical energy in the case of AlSi12 matrix, however, the energy absorption efficiency due to the different failure mechanism of AMSFs (homogeneous densification in the case of Al99.5 and cleavage in the case of AlSi12 matrix, respectively). The DMA tests confirmed the effective Young's moduli values, measured by compression and proved higher damping capability in the case of AlSi12 matrix. FEM and analytical calculations also confirmed the measured effective Young's moduli within a reasonable error band.

Bimodal poly(methyl methacrylate) (PMMA) foams are produced with a new method combining syntactic foam production and supercritical CO2 (scCO2) foaming. Bimodal pore structure offers several potential advantages to foam properties, such as reduced mass density and excellent thermal and sound insulation properties. To produce the foams, first PMMA composites are produced with hollow glass microspheres (HGMs) and octatrimethylsiloxy polyhedral oligomeric silsesquioxane (POSS) nanoparticles using a twin screw extruder. The composite syntactic foams are then processed with scCO2 to form bimodal pore structured PMMA-HGM-POSS composite foams. In the foam matrix, large pores form due to the CO2 diffusion in the matrix towards the voids between the matrix and HGM surfaces, and small pores are formed at the nucleation cites. Highly CO2-philic POSS nanoparticles contribute to scCO2 foaming as cell nucleators enhancing the foaming performance of the syntactic composites. The effects of process pressure, time, and concentrations of HGMs and POSS nanoparticles on the foam morphology are studied. The highest decrease achieved in the foam density compared to that of the bulk polymer is 69% with only 12% decrease in the hardness.

Because the aerogel has ultra-low density and good impact resistance, the aerogel material, epoxy-hardener system, and expandable polystyrene beads (EPS) were used to prepare the lightweight aerogel reinforced hollow epoxy macro-spheres (AR-HEMS). The multi-phase epoxy syntactic foam (ESF) was manufactured with the epoxy-hardener system, HGMS (EP-hardener-HGMS), and AR-HEMS by “the compression modeling method.” In this experiment, in order to enhance the strength of the ESF, some different kinds of the carbon fiber (CF) were added into the EP-hardener-HGMS system (CFR-EP). The influence of the volume stacking fraction, inner diameter, and layer of the AR-HEMS and the content and type of the CF in the EP-HGMS (CFR-EP) system on the compressive strength of the ESF were studied. Weighing the two factors of the density and compressive strength, the ESF reinforced by 1.5 wt% CF with 90% AR-HEMS has the better performance. This kind of the ESF has 0.428 g/cm3 nd 20.76 Mpa, which could be applied in 2076 m deep sea.

In this study, the impact behavior of sandwich panels of natural rubber-based syntactic foam cores with aluminum face sheets was investigated experimentally and with the help of finite element analysis (FEA). Syntactic foam cores were produced byadding glass bubbles (GB) to the natural rubber (NR). Natural rubber was dissolved at room temperature with chemical solvents mixed with glass bubbles at 10, 20, and 30 weight percentages. Very low density (~0.8 g × cm-3) and high compressible foams were obtained depending on the GB weight percentages. Aluminum face sheets and the NR/GB syntactic foam core developed were joined by adhesive bonding to produce sandwich beam specimens. The sandwich beams manufactured in this way were subjected to impact loading under three-point bending boundary conditions experimentally. The experimental results were compared with finite element simulation results under the same loading and boundary conditions. The damage mechanism of the sandwich panels devised were analyzed. According to the results, natural rubber containing an additive of 20 wt.-% GBs showed better impact resistance than the others.

The role played by hollow ceramic thin-walled aluminium oxide microballoons on the shear deformation characteristics of AZ31 Magnesium syntactic foam is studied through high-speed machining. The ceramic microballoons embedded in the AZ31 matrix provides the necessary stiffness for these novel foams. The effect of hollow ceramic microballoon properties, such as the volume fraction, thin wall thickness to diameter ratio, and microballoon diameter, profoundly affects the chip formation. A novel force model has been proposed to explain the causes of variation in cutting forces during chip formation. The results showed an increase in machining forces during cutting AZ31 foams dispersed with higher volume fraction and finer microballoons. At a lower (Davg/h) ratio, the mode of microballoon deformation was a combination of bubble burst and fracture through an effective load transfer mechanism with the plastic AZ31 Mg matrix. The developed force model explained the key role played by AZ31 matrix/alumina microballoon on tool surface friction and showed a better agreement with measured machining forces.

This paper introduces a novel functionally graded metallic syntactic foam. The investigated foams are manufactured while using infiltration casting where molten A356 aluminum flows into the interstitial voids of packed expanded perlite (EP) particle beds. The partial pre-compaction of particle beds enables the creation of distinct and reproducible density gradients within the syntactic foam. In this study, the samples are produced using four gradually increasing compaction forces and are compared to non-compacted samples. X-ray imaging is used to detect the resulting spatial variation of foam density. In addition, quasi-static compression tests are performed to determine the mechanical foam properties. The results suggest that particle pre-compaction is an efficient tool for tailoring the density and mechanical properties of these novel functionally graded materials.

Thermoplastic Elastomer Vulcanized (TPE-V) syntactic foams made by Thermo-Expandable Microcapsules (TEMs) are becoming of a large interest for automotive industry. TPE-Vs combine advantages of class rubber compound properties with an easier manufacture process and are recyclable. Therefore, TPE-Vs are more and more used to manufacture automotive sealing system by an extrusion process, which is the focus of this research. Due to the two-phase structure of TPE-V, classical extrusion foaming technologies, such as chemical and physical foaming, are complex to be controlled. Thus, TEMs show an outstanding ability to be effective and produce repeatable microstructure with standard extrusion equipment. TEMs consist in a mixture of liquid hydrocarbons, encapsulated by a gas-proof polymeric shell. Exposed to elevated temperatures, the internal pressure drives the dilation of the TEMs, as a result a TPE-V syntactic foam is produced. The aim of this study is to understand where the expansion occurs and how can it be affected by extrusion process parameters. Temperature is a well-known key parameter to control final expansion of TEMs. Hence, measurements at high pressure and temperature were done to find out the location of expansion during extrusion process. Additionally, we have designed three groups of three dies to apply different pressure drops, pressure drop rates and residence time, inside the die. Under these process conditions, density, cell microstructure and viscosity have been investigated.

Metal matrix syntactic foams are particulate composite foams composed of a supporting metal matrix and high-strength hollow particles. These materials have higher specific strengths and specific stiffnesses compared to solid metals and metal foams. The reinforced porosity in these foams is the primary cause of this increase in strength-to-density ratio. Metal matrix syntactic foams can be difficult to manufacture, however, without extensive fracture of the hollow particles. The first goal of this study was to optimize a water-based binder for low-pressure injection molding of metal matrix syntactic foams. The optimized binder composition was 7% agar, 4% glycerin, and 89% water. The second goal of this study was to test the material compatibility between silicate glass materials and copper alloys. It was found the common copper sintering aids reacted negatively with silicate glasses such that they melted at or below the sintering temperature of the metal. Pure copper does not have this issue, but it is conversely difficult to sinter to full density.

Metal matrix syntactic foams (MMSF) are foam composites obtained by filling hollow and/or porous particles into a metal matrix. MMSF are promising materials in defense, aerospace, automotive, marine and engineering applications. Mechanical and physical properties of MMSF can be tailored to reach better structural and/or functional behaviors by fitting processing and tailoring parameters. Some of these parameters are: reinforcement size, volume fraction, distribution of reinforcements and chemical composition. Three techniques are available to manufacture MMSF: Stir casting/vortex method (SC), powder metallurgy (P/M) and infiltration routes. Infiltration process is by far the main employed for making MMSF, it allows a large range of reinforcement (30 vol % to 78 vol %) and offers great advantages compared to other techniques. This paper reviews infiltration routes used to date, their advantages and drawbacks, the main processing parameters of each route, and a relation of representative studies developed to date on the synthesizing of MMSF by molten infiltration processes.

Metal matrix syntactic foams have been attracting considerable attention in recent years due to their potential applications in lightweight structures and energy absorption. In this paper, CF-8 cast austenitic stainless steel with hollow Al2O3 spheres’ syntactic foams was prepared by infiltration casting technology. The effects of preheat temperature of ceramic mold and diameter of hollow ceramic spheres on the forming ability of infiltration casting of syntactic foams were investigated and the results showed that suitable preheat temperature of ceramic mold is a necessary prerequisite to produce the syntactic foams. And then, the quasi-static compressive behavior of these foams was studied by experimental and numerical simulation and the energy absorption capacity is evaluated.

Syntactic foam is being increasingly conceived for aero engine applications to enhance overall structural reliability under impact loading. Systematic compressive tests without and with lateral confinement are carried out to investigate the deformation and failure of an epoxy syntactic foam (ESF) at quasi-static 0.01/s, medium rate 10–100/s and high strain rates 500–1100/s at gradually increasing temperatures from room temperature 25 °C to 150 °C. The stress–strain response and the corresponding deformation process, complemented by Digital Image Correlation (DIC) technique, were monitored to reveal the dynamic deformation and strain localization of the foam. The elastic-brittle behavior without confinement at high strain rates can be suppressed by the lateral confinement and by elevated temperatures above 100 °C. The lateral confinement slightly increases yield stress and significantly improves the energy absorption of ESF. Both confined yield stress and energy absorption evolve nonlinearly with strain rate and temperature. The strain hardening in the elastic–plastic behavior of ESF under confinement is strain rate independent, compared to its modest temperature dependency. A nonlinear phenomenological model is found to be able to describe the unconfined and confined responses of ESF and its temperature-strain rate equivalence, and reveal the competition between strain hardening and strain softening which is influenced by temperature.

The nickel thin-walled hollow spheres (NHS) epoxy syntactic foam was fabricated by the infiltration method. The crystal structure and grain size of the NHS were quantitatively analyzed by FIB-TEM. The bulk compressive response of the NHS syntactic foam was determined and compared with glass bubble syntactic foam. The X-ray computed microtomography (XCT) coupling with the interrupted compression tests were conducted on a single NHS and the NHS syntactic foam to demonstrate the 3D deformation history. The bulk behaviors of the NHS syntactic foam were correlated with the XCT examinations to analyze the mechanisms of the failure process. The electrodeposited NHS shows the nanocrystalline and polycrystalline microstructure. The low air void content was achieved in the NHS syntactic foam produced by the infiltration method. Although the NHS syntactic foam's elasticity and yield strength are lower, the compressive resistance and toughness as well as the energy absorption of the NHS syntactic foam are higher than those of glass syntactic foam. The failure process of the NHS syntactic foam is dominated by the NHSs deformation and the resultant strain hardening. The damage initiates from the weak NHSs, then more crushed bands arise with the increased compressive stress. The further deformation of the damaged bands can intermittently develop owing to the strain hardening. During the deformation history, no visible macro cracks can be found in the epoxy matrix from the XCT slices.

Syntactic foams comprising glass or thermoplastic microballoons have gained considerable attention in recent years due to mechanical and thermal properties that are advantageous for naval and aerospace applications. This work reports a method for producing syntactic foams with unusually high-volume fraction microballoon loadings (>0.74) and its utilization for the creation of “hybrid” epoxy resin-based syntactic foams comprising various mixtures of glass and thermoplastic microballoons. Microstructural analyses using X-ray micro-computed tomography provided non-destructive quantitative characterization of microballoon packing, confirming the high loading levels suggested by density measurements. By systematically varying the glass/thermoplastic microballoon ratio, it was shown that a range of mechanical properties can be engineered into these lightweight materials. The peak impact force of these syntactic foams can be significantly reduced (∼30% reduction) through combining glass and thermoplastic microballoons in a ratio where the thermoplastic microballoons are the dominant fraction but not the sole microballoon component.

© 2018 Trans Tech Publications, Switzerland. The behaviour of aluminium matrix syntactic foams (AMSFs) with homogeneous and graded structures have been studied under quasi-static compression and impact. Particle size of ceramic microspheres and impact velocity had significant effects on the static and impact responses. Smaller microspheres led to higher strength but lower toughness. The compressive yield stress, plateau stress and specific energy absorption of the graded AMSF specimens were approximately the averages of the constituent layers, following the rule of mixture, although the order of the layers had some influence on the compressive behaviour. The syntactic foams were brittle under impact, no matter whether they were brittle or ductile in quasi-static compression. They had higher peak stresses and absorbed more energy in impact than in quasi-static compression. The location of the most brittle layer of the small ceramic microspheres had a significant effect on the impact failure pattern and sequence of the three-layer graded AMSFs.

In this paper, the effect of arctic conditions on the flexural response of cenosphere/epoxy syntactic foams is investigated. Understanding the behavior of such foams under extreme conditions is critical for exploring their suitability for constructing lightweight platforms used in arctic explorations. Such platforms are exposed to subzero temperatures for extended periods of time potentially degrading their mechanical properties. In the research study presented here, samples of cenosphere/epoxy syntactic foams were conditioned under arctic environment at −60 °C temperature for a period of 57 days. Flexural tests were then conducted at room temperature as well as in-situ −60 °C on the conditioned samples and compared against unconditioned samples. Combinations of surface modification and cenosphere volume fractions were considered. Experimental findings showed that an increase in flexural modulus can be observed at room temperature with increasing cenosphere volume content for both untreated and treated cenosphere reinforced syntactic foams. In contrast, a decrease in flexural strength was observed as compared to neat resin. For the case of arctic exposed samples, an apparent increase in flexural modulus was recorded between 7-15% as compared to room temperature cenospheres/epoxy syntactic foams. In addition, an apparent increase of 3–80% in the flexural strength was observed under arctic environment. The conditioning of cenosphere/epoxy syntactic foams under low temperatures manifested lower strains to failure as compared to neat epoxy and they exhibit quasi-brittle behavior leading to sudden failure in the post peak regime.