Matrix Syntactic Foams Research Articles

Controlled Shrinkage of Expanded Glass Particles in Metal Syntactic Foams.

Metal matrix syntactic foams have been fabricated via counter-gravity infiltration of a packed bed of recycled expanded glass particles (EG) with A356 aluminum alloy. Particle shrinkage was studied and has been utilized to increase the particles’ strength and tailor the mechanical properties of the expanded glass/metal syntactic foam (EG-MSF). The crushing strength of particles could be doubled by shrinking them for 20 min at 700 °C. Owing to the low density of EG (0.20–0.26 g/cm3), the resulting foam exhibits a low density (1.03–1.19 g/cm3) that increases slightly due to particle shrinkage. Chemical and physical analyses of EG particles and the resulting foams were conducted. Furthermore, metal syntactic foam samples were tested in uni-axial compression tests. The stress-strain curves obtained exhibit three distinct regions: elastic deformation followed by a stress plateau and densification commencing at 70–80% macroscopic strain. Particle shrinkage increased the mechanical strength of the foam samples and their average plateau stress increased from 15.5 MPa to 26.7 MPa.

Enhancing the Ignition, Hardness and Compressive Response of Magnesium by Reinforcing with Hollow Glass Microballoons.

Magnesium (Mg)/glass microballoons (GMB) metal matrix syntactic foams (1.47–1.67 g/cc) were synthesized using a disintegrated melt deposition (DMD) processing route. Such syntactic foams are of great interest to the scientific community as potential candidate materials for the ever-changing demands in automotive, aerospace, and marine sectors. The synthesized composites were evaluated for their microstructural, thermal, and compressive properties. Results showed that microhardness and the dimensional stability of pure Mg increased with increasing GMB content. The ignition response of these foams was enhanced by ~22 °C with a 25 wt % GMB addition to the Mg matrix. The authors of this work propose a new parameter, ignition factor, to quantify the superior ignition performance that the developed Mg foams exhibit. The room temperature compressive strengths of pure Mg increased with the addition of GMB particles, with Mg-25 wt % GMB exhibiting the maximum compressive yield strength (CYS) of 161 MPa and an ultimate compressive strength (UCS) of 232 MPa for a GMB addition of 5 wt % in Mg. A maximum failure strain of 37.7% was realized in Mg-25 wt % GMB foam. The addition of GMB particles significantly enhanced the energy absorption by ~200% prior to compressive failure for highest filler loading, as compared to pure Mg. Finally, microstructural changes in Mg owing to the presence of hollow GMB particles were elaborately discussed.

Synthesis and characterization of hollow glass microspheres reinforced magnesium alloy matrix syntactic foam

In the present scenario, a considerable importance is being given to find newer materials for marine applications. An endeavour has been made to synthesis hollow glass microspheres reinforced magnesium matrix (AZ91D/HGM) syntactic foams and analyze its mechanical properties for such applications in the present study. The 40 μm size reinforcement particles have been added with matrix under dissimilar mass fractions of 15%, 20% and 23% to investigate the interfacial reaction, compressive properties, hardness, density, porosity, corrosion resistance. From the experimental investigation, it has been inferred that the density of foams and corrosion rate have been considerably reduced owing to increase in reinforcement mass fraction. It has also been observed that the developed syntactic foam has produced higher compressive strength due to its cushion effect and higher plateau stress. From the porosity phase analysis, it has been found that the porosity has been increased with increasing mass fraction percentage. From the composition structural analysis, Mg17Al12 has been observed as main interfacial reaction between the microsphere and matrix alloy.

Quasi-static and dynamic compression behavior of glass cenospheres/5A03 syntactic foam and its sandwich structure

5A03 aluminum matrix syntactic foam filled with glass cenospheres was synthesized using pressure infiltration technique. This paper focused on the compression behavior of syntactic foam at quasi-static (10−3s−1) and dynamic (strain rate 1×103s−1–3×103s−1) condition, and the dynamic response of syntactic foam core sandwich structure with two different wave impedance front-panels (A3 steel and AZ31) subjected to split-Hopkinson pressure bar. The syntactic foam at dynamic loading exhibited a maximum 43% increase in peak strength, 38% in plateau strength, and 23% in energy absorption capacity compared to quasi-static results, with 0.03 strain rate sensitivity similar to that of aluminum matrix. The dynamic compression behavior can be concluded as thin near-45° shear bands forming, deformed area propagating to the central and lateral parts, and finally densifying with significant lateral expansion. The sandwich structure exhibited great energy absorption capability due to the syntactic foam core. The higher wave impedance front-panel would be conducive to the energy absorption capability of syntactic foam core into full play.

Microstructure and strength correlation of pure Al and Al-Mg syntactic foam composites subject to uniaxial compression

The microstructure and quasi-static compression of glass cenospheres/aluminum matrix syntactic foams (AMSFs) with three t/R ratio cenospheres (t/R=0.043, 0.052 and 0.064) and three different matrices (cp-Al, 5A03 and 5A06) were investigated. The compression strength and energy absorption of foams were found to increase with t/R ratio and Mg in matrix. The strengthening mechanisms were attributed to the nature properties of cenospheres and the thickness of high strength interfacial reaction MgAl2O4 forming. Two models were provided to predict the quasi-static properties of AMSFs considering the factors including physical properties of matrix and cenospheres, volume fraction of cenospheres, composition changing of matrix and thickness of interfacial reaction coating caused by interfacial reaction between matrix and cenopsheres. The predictions for peak stress, plateau stress, energy absorption capacity and specific energy absorption of AMSFs showed good agreement with experimental data. The Al-Mg syntactic foams in this study exhibited high specific energy absorption (56Jg−1) and specific plateau strength (94MPacm−3g−1).

Structural Damages in Syntactic Metal Foams Caused by Monotone or Cyclic Compression

Closed cell, high strength metallic foams, like ceramic hollow spheres filled metal matrix foams are promising materials to build lightweight but high specific strength structural parts. The aim of this study is to investigate the damage of the foam structure during monotone or cyclic compression. The tested metal matrix syntactic foams were produced by inert gas pressure infiltration. Four different alloys as matrix and two different ceramic hollow spheres as filler material were applied. The cylindrical specimens were investigated in quasi-static and high strain rate compression and in cyclic compression. The higher strain rates were ensured by a Split-Hopkinson pressure bar system, while the fatigue tests were performed on a closed loop universal hydraulic testing machine. The failure modes of the foams have explicit differences showing barreling and shearing in the case of quasi-static and high strain rate compression respectively. In the case of the fatigue loading, there was a significant difference between the damage mechanisms of the unalloyed and the Si alloyed matrix syntactic foams. This can be explained by the difference between the yield strength of the matrix material and the ceramics hollow spheres.

The Effect of Matrix Composition on the Deformation and Failure Mechanisms in Metal Matrix Syntactic Foams during Compression.

The influence of the matrix material on the deformation and failure mechanisms in metal matrix syntactic foams was investigated in this study. Samples with commercially pure Al (Al) and Al-12 wt % Si (AlSi12) eutectic aluminum matrix, reinforced by hollow ceramic spheres, were compressed at room temperature. Concurrently, the acoustic emission response and the strain field development on the surface were monitored in-situ. The results indicate that the plastic deformation of the cell walls is the governing mechanism in the early stage of straining for both types of foams. At large stresses, deformation bands form both in the Al and AlSi12 foam. In Al foam, cell walls collapse in a large volume. In contrast, the AlSi12 foam is more brittle; therefore, the fracture of precipitates and the crushing of the matrix take place within a distinctive deformation band, along with an occurrence of a significant stress drop. The onset stress of ceramic sphere failure was shown to be not influenced by the matrix material. The in-situ methods provided complementary data which further support these results.

Electrochemical evaluation of sintered aluminium – ceramic cenospheres composites

ABSTRACTThe corrosion behaviour of cenospheres metal matric syntactic foams of different compositions in 3.5 wt-% NaCl aqueous solution at ∼25°C was investigated. The electrochemical properties of the composites were assessed experimentally, employing potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. Appropriate equivalent electrical circuits were proposed. Results showed that the corrosion rate is higher for the metal matrix syntactic foams compared to pure sintered aluminium. As the volume fraction of cenospheres increases cenospheres fragments and the presence of reaction zones seems to have a greater effect on the corrosion behaviour of the composites compared to the presence of unintended porosity.

Vibration-Assisted Sputter Coating of Cenospheres: A New Approach for Realizing Cu-Based Metal Matrix Syntactic Foams

The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means of vibration-assisted magnetron sputtering yields a starting material with considerable potential for the production of new types of metal matrix syntactic foams as well as optimized variants of conventional materials of this kind. This study introduces the coating process and the production of macroscopic samples from the coated spheres via spark plasma sintering (SPS). The influence of processing parameters on the coating itself, and the syntactic foams are discussed in terms of the obtained density levels as a function of sintering temperature (which was varied between 850 and 1080 °C), time (0.5 to 4 min), and surface appearance before and after SPS treatment. Sintering temperatures of 900 °C and above were found to cause breaking-up of the homogeneous sputter coating into a net-like structure. This effect is attributed to wetting behavior of Cu on the alumino-silicate cenosphere shells. Cylindrical samples were subjected to conductivity measurements and mechanical tests, and the first performance characteristics are reported here. Compressive strengths for Cu-based materials in the density range of 0.90–1.50 g/cm3 were found to lie between 8.6 and 61.9 MPa, depending on sintering conditions and density. An approximate relationship between strength and density is suggested based on the well-known Gibson–Ashby law. Density-related strength of the new material is contrasted to similar findings for several types of established metal foams gathered from the literature. Besides discussing these first experimental results, this paper outlines the potential of coated microspheres as optimized filler particles in metal matrix syntactic foams, and suggests associated directions of future research.

Mechanical Properties of Epoxy Matrix-Borosilicate Glass Hollow-Particle Syntactic Foams

Abstract Syntactic foams are particulate composites, which consist of a dispersion of hollow particles in a matrix. These materials are extensively used in the structures of underwater vehicles, but existing studies have shown that the commonly used soda-lime–borosilicate glass hollow particles are susceptible to significant degradation upon exposure to moisture. In this work, epoxy matrix syntactic foams are fabricated using borosilicate glass hollow particles that are not susceptible to degradation in wet environments. Nine compositions are fabricated and tested for quasi-static compressive properties, high-strain-rate compressive properties, and flexural properties. The quasi-static compressive strength and energy absorption are found to increase with composite density and the compressive strength is found to exceed that of similar syntactic foams using soda-lime–borosilicate hollow particles. The syntactic foams were observed to have 70 %–108 % higher peak stress in the high-strain-rate regime compared to the quasi-static values but the strength within the high-strain-rate regime was not dependent on the strain rate. The flexural properties were shown to have strong sensitivity to volume fraction of hollow particles.

Evaluation of the dynamic properties of an aluminum syntactic foam core sandwich

The purpose of this study is to evaluate the dynamic mechanical properties of syntactic foam core sandwich structures. Aluminum matrix syntactic foams with carbon fabric skins are studied. Syntactic foams incorporate porosity in their foam-like structure by means of hollow particles. The material examined here is composed of a core made of aluminum A356 matrix filled with alumina hollow particles. Two types of sandwich composites are studied containing: (a) a single layer of carbon fabric and (b) three layers of the same fabric in 0°/90° orientation. Dynamic characterization was conducted using a free vibration method to determine the resonant frequency of the sandwich beams. The dynamic modulus, storage modulus, loss modulus and damping ratio were calculated from the test results. The experimental results were used to validate the predictions of a theoretical model. The experimental values for Young's modulus of one- and three-layer fabric sandwiches were measured to be 32.57 ± 2.15 and 37.33 ± 1.12 GPa, respectively. The experimental results are in close agreement with the theoretical model.

High Strain Rate Tensile and Compressive Testing and Performance of Mesoporous Invar (FeNi36) Matrix Syntactic Foams Produced by Feedstock Extrusion

The present study investigates the high strain rate behavior of mesoporous metal matrix syntactic foams focusing on the dependence of compressive and tensile properties on strain rate. The strain rate range, covered both in compression and tension, extends from quasi‐static conditions or 10−3 s−1 to 103 s−1. Syntactic foams based on commercial high strength hollow glass microspheres and Invar (FeNi36) matrix are produced by means of feedstock extrusion and subsequent sintering. Levels of glass microsphere addition examined are 5 and 10 wt%, respectively, corresponding to approximately 40 and 60 vol% of microspheres in the initial mix prior to sintering, and considering the metal and filler fraction only. Reference samples containing no microsphere addition have been included in the study. Mechanical testing is accompanied by metallographic examinations.

Fatigue properties of ceramic hollow sphere filled aluminium matrix syntactic foams

Metal matrix syntactic foams, consisting of two grades of aluminium alloys and a set of oxide ceramic hollow spheres, were investigated in the aspect of cyclic loading. The results of the compressive – compressive cyclic loading with the load asymmetry factor of R=0.1 ensured full reliability design data for the investigated material in the lifetime region, while the fatigue limits were determined by staircase method. Based on the measurements the Wöhler curves of the foams were constructed, including the median curves, their confidence boundaries and the fatigue strength. Regarding the matrix material, the softer matrix ensured higher load levels for the fatigue strength than the more rigid matrix. Considering the size of the reinforcing ceramic hollow spheres, larger spheres performed better than the more vulnerable smaller ones. One common failure mode was isolated for the investigated foams: the samples were broken along a shear band, similar to the case of quasi-static loading.

Fatigue properties of expanded perlite/aluminum syntactic foams

The main purpose of this paper is to present the basic fatigue properties of metal matrix syntactic foams. The investigated syntactic foams consisting of expanded perlite and A356 aluminum matrix were produced using an inert gas pressure infiltration technique. The obtained foams were subjected to cyclic compressive loading in order to investigate their fatigue properties. The standard procedure for cyclic fatigue testing was slightly modified to account for the variation of porosity and strength which is typical for metallic foam samples. This approach allows the direct comparison of the fatigue test results between all investigated samples. Depending on the applied load level, two different failure mechanisms were identified that resulted in characteristic deformation – loading cycle curves. The failure mechanisms were further investigated on the microstructural scale: traces of fatigue beachmarks and extensive plastic deformation were found. Furthermore, Wöhler-like deformation – lifetime diagrams were created in order to predict the expected lifetime of the properties of metal matrix syntactic foams .

Effect of cenosphere surface treatment and blending method on the tensile properties of thermoplastic matrix syntactic foams

ABSTRACTThe influence of cenosphere surface treatment and blending method on the properties of injection molded high‐density polyethylene (HDPE) matrix syntactic foams is investigated. Cenospheres are treated with silane and HDPE is functionalized with dibutyl maleate. Tensile test specimens are cast with 20, 40, and 60 wt % of cenospheres using injection molding. Modulus and strength are found to increase with increasing cenosphere content for composites with treated constituents. Highest modulus and strength were observed for 40 and 60 wt % untreated mechanically mixed and treated brabender mixed cenospheres/HDPE blends, respectively. These values are 37 and 17% higher than those for virgin and functionalized HDPE. Theoretical models are used to assess the effect of particle properties and interfacial bonding on modulus and strength of syntactic foams. Brabender mixing method provided highest ultimate tensile and fracture strengths, which is attributed to the effectiveness of Brabender in breaking particle clusters and generating the higher particle–matrix surface area compared to that by mechanical mixing method. Theoretical trends show clear benefits of improved particle–matrix interfacial bonding in the strength results. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43881.

Quasi-static and high strain rates compressive behavior of aluminum matrix syntactic foams

Abstract The compressive deformation behavior of aluminum matrix syntactic foams with varying cenosphere sizes have been studied at varying strain rates (from 10 to 3∼103 s −1 ). The results showed that the size of the cenospheres and the strain rates had significant effects on the compressive properties. The smaller cenospheres ensured higher compressive strength due to fewer flaws in the microstructure and better mechanical stability. The energy absorption of the present syntactic foam was found to increase with an increase in strain rates. Compared to the conditions under quasi-static loading, the energy absorption capacity of syntactic foam exhibited 75–85% more under dynamic loading. The different compressive failure characteristics of syntactic foams could be attributed to the unit of shear displacement which got smaller with the increasing strain rates. These foams showed pronounced energy absorption capabilities, suggesting their potential for use in blast and impact protection.

Mechanical behavior of pure Al and Al–Mg syntactic foam composites containing glass cenospheres

Glass cenospheres were used as space holders for making aluminum matrix syntactic foams by pressure infiltration technique. The mechanical properties and failure behavior of cenospheres/Al syntactic foams with pure Al and Al–Mg alloys were investigated in the present work. The failure behavior of cenospheres in two syntactic foams was similar. However, the mechanical behavior of these two syntactic foams was different. Under compression process, the cenospheres/pure Al showed discontinuous shear band and drum shape, while cenospheres/Al–Mg exhibited continuous shear band and was divided by main shear zone. At the tensile state, the cenospheres in pure Al matrix syntactic foam debonded from the matrix, while the cenospheres in Al–Mg matrix syntactic foam was well-bonded and appeared to lamellar tearing. It is suggested that the difference of mechanical deformation behavior could be attributed to the matrix ductility and the forming of interfacial reaction product MgAl2O4 coatings.

Quasi-Static and High Strain Rate Compressive Response of Injection-Molded Cenosphere/HDPE Syntactic Foam

High strain rate compressive properties of high-density polyethylene (HDPE) matrix syntactic foams containing cenosphere filler are investigated. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10−4 s−1, 10−3 s−1 and 10−2 s−1 strain rates. Further, a split-Hopkinson pressure bar is utilized for characterizing syntactic foams for high strain rate compression. The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10−4 s−1 for HDPE resin and syntactic foams. Theoretical models are used to estimate the effectiveness of cenospheres in reinforcing syntactic foams.

Effects of Hollow Fly-Ash Particles on the Properties of Magnesium Matrix Syntactic Foams: A Review

Abstract In the past decade, magnesium has been seen as one of the most potential metals for weight-critical engineering applications. As magnesium is the lightest structural metal, it has higher weight-saving capabilities when compared to aluminum. Significant research efforts have been carried out on magnesium matrix alloys and composites to tailor and enhance mechanical properties based on end applications. This paper provides a review on fly-ash-reinforced magnesium matrix syntactic foams. Fly-ash cenospheres are made up of mainly alumina and silica and also contains large number of trace elements, which makes it intriguing to analyze the microstructure and interfacial responses of the end composites. In comparison with aluminum matrix syntactic foams, the research on magnesium matrix syntactic foams is still at an incipient stage. This paper provides an insight on processing techniques, microstructural and mechanical evaluations of pure Mg, AZ, and ZC alloy series, and their syntactic foams. This paper also reviews the weight-saving ability of magnesium matrix syntactic foams and their potential scope and applications.

Monitoring the failure mechanisms in metal matrix syntactic foams during compression by acoustic emission

Syntactic foam containing hollow ceramic spheres with an average outer diameter of 1.45mm and wall thickness of 58µm was produced using the pressure infiltration technique. This paper presents the analysis of the compressive deformation mechanisms of these syntactic foams using the acoustic emission (AE) technique. The active deformation mechanisms are determined by sequential k-means analysis of the AE data. The analysis revealed three dominant deformation mechanisms: plastic deformation of the cell walls, sphere fracture, and cell wall collapse. The AE results obtained are in good correlation with the findings of the visual inspection of the surface of the specimen, suggesting that the active deformation mechanisms in the whole volume of the specimen can be determined by this technique.