Matrix Syntactic Foams Research Articles

Unidirectional steel wire reinforced metal matrix syntactic foams

Abstract A double composite structure has been successfully produced using vacuum infiltration. In this structure, the matrix was unalloyed aluminium filled with Lightweight Expanded Clay Aggregate Particles to create metal matrix syntactic foam, and stainless steel wires were placed inside this matrix as unidirectional reinforcement. The wires created a shape-locking bond with the matrix owing to their wave-like form, which helped to prevent reinforcement pullout. Based on the acquired tensile data, the tensile strength of the specimens calculated with the theoretical maximum area of reinforcement wires is Rm, theoretical = 1063 ± 192 MPa, while the tensile strength of the individual wires is Rm, wires = 882 ± 2, which leads to the conclusion that the matrix distributed some of the stress.

Unidirectional fibre reinforcement of syntactic metal foams

Abstract Metal matrix syntactic foams are porous structures where the porosity is formed by introducing a porous filler material into the metal matrix. They have low density and absorb significant energy during compression but cannot withstand tensile stress. The main goal of this study was to apply unidirectional fibre reinforcement to syntactic metal foams. Therefore, a lightweight double-composite structure that can be utilised against tensile load and has advantageous properties during compression was created. Copper-nickel coated carbon fibre bundles were used as unidirectional long fibre reinforcement, lightweight expanded clay aggregate particles as filler material and Al99.5 aluminium as matrix material. The samples were created with vacuum infiltration and formed into cylindrical tensile specimens. Quasi-static tensile tests were carried out on the specimens and fibre trusses, and quasi-static compression was applied on specimens in the parallel and perpendicular direction to the unidirectional fibre truss.

Effect of the heat treatment on the compression of Cu20Sn matrix syntactic foams reinforced with Fe-hollow spheres

This work analyzes the manufacturing process, phase transformations and compression behavior of un-treated and heat-treated syntactic foams consisting of a Cu20Sn alloy matrix reinforced with Fe-hollow spheres. Manufacturing process included the infiltration of the molten alloy into preforms of spheres sintered at 1000 °C during 1 h, obtaining syntactic foams with porosities near 52 %. These foams were heat-treated at 750 °C for 1 h, followed by quenching in water, which led to phase transformations from ε to β. This fact improved the compressive properties of the foams, increasing compression strengths from 195 to 243 MPa. Interfaces were not found between matrix and the Fe-hollow spheres.

Mechanical Properties of Aluminum Matrix Syntactic Foams Manufactured with Aluminum Smelter Waste

Aluminum smelter waste (ASW) is a big contributor to landfill and its recycling has been of great interest. This study characterizes the ASW powder, manufactures aluminum matrix syntactic foams using ASW, and investigates their mechanical properties. Different particle size groups of the ASW powder contain different impurities and porosities, leading to different strengths. The mechanical behaviors of the ASW syntactic foams are similar to existing metal matrix syntactic foams. The compressive yield strength, plateau strength, and specific energy absorbed vary in the ranges of 111–398, 33–145 MPa, and 18–71 MJ m−3. The flexural strength and flexural modulus vary in the ranges of 8–138 MPa and 13–72 GPa. The peak impact strength and impact energy in drop‐weight impact vary in the ranges of 192–547 MPa and 16–29 J. Particle size and heat treatment of the ASW powder have significant effects on the properties and brittleness of the resultant syntactic foam.

Tribological Properties of Aluminium Matrix Syntactic Foams Manufactured with Aluminium Smelter Waste

Aluminium smelter waste (ASW) is a big contributor to landfills, and its recycling has been of great interest. This study investigates the tribological properties of aluminium matrix syntactic foams manufactured using an Al 6082 alloy and ASW. Ball-on-disc tests were conducted under both dry and lubricated conditions. Under dry sliding conditions, the coefficient of friction (COF) had an initial sharp increase, followed by a gradual decrease and finally a steady state as the sliding distance increased. The wear surfaces showed the presence of adhesive, abrasive and oxidative wear, with some presence of delamination. Syntactic foams containing small ASW particles led to a decrease in surface roughness, decrease in the average COF and decrease in specific wear. Heating large ASW particles before manufacturing the syntactic foams enhanced overall wear properties because the particles are hardened due to a compositional change. The T6 treatment of the syntactic foams enhanced the wear properties due to the hardening of the Al matrix. The average COF of the ASW syntactic foams was higher than that of the E-sphere syntactic foam, which was predominantly abrasive wear. The specific wear of the ASW syntactic foams can be higher or lower than the E-sphere syntactic foam, depending on the ASW particle size. Under lubricated sliding test conditions, the wear was reduced significantly, and the type changed from predominantly adhesive to predominantly abrasive. The porous ASW particles acted as lubricant reservoirs and provided a constant supply of lubricant, further improving the lubrication effect.

Effect of hollow glass microspheres surface modification on the compressive strength of syntactic foams

Polymer matrix syntactic foams made of hollow glass microspheres (HGMs) and epoxy resin are widely used in underwater vehicles providing buoyancy due to their advantages of low density and high mechanical strength. When HGMs is strong enough, surface modification of HGMs is an effective method to improve the compressive strength of syntactic foams. However, the effects of different surface modifiers on the physical properties of HGMs and the compressive strength of syntactic foams have rarely been systematically studied. It is of great significance to enhance the interfacial strength of syntactic foams. Herein, the T40 HGMs was treated by different modifiers (HCl, NaOH, Li2SiO3, Me3SiONa, KH550, KH560, KH570, and Volan), physical properties of modified HGMs were studied, including true density, angle of repose, isostatic compressive strength, specific surface area, and contact angle. Furthermore, the effects of modified HGMs on the compressive strength of syntactic foams were also studied. The results showed that the compressive strength depend largely on the interface bonding between HGMs and resin matrix. This work can provide some references for mechanical property reinforcement of syntactic foams with high filling ratio and plenty of interface zones.

Thermal and mechanical properties of AlSi7Mg matrix syntactic foams reinforced by Al2O3 or SiC particles in matrix

Materials with complex inner structure can be challenging to characterise in an effective way. The effective material parameters significantly depend on the structure, and thus on the interface properties. In the present paper, we focus on metal matrix syntactic foams, and we attempt to determine their effective thermal parameters. We supplement the results with their mechanical properties as well. For thermal characterisation, we use the heat pulse experiment to study their transient thermal response. We observed deviation from Fourier's law in multiple situations, and thus we propose an evaluation procedure for such experimental data using the Guyer–Krumhansl heat equation. We provide an iterative procedure to efficiently find the effective thermal diffusivity values provided by the Guyer–Krumhansl and Fourier equations based on the measured transient response. Furthermore, we studied the effective parameters, the specific heat, mass density, thermal conductivity and thermal diffusivity. We found that the standard estimations significantly overestimate the thermal conductivity. Furthermore, we propose a method for deducing a more reliable thermal diffusivity and thermal conductivity based on the transient temperature history, i.e., we propose to estimate Fourier's thermal diffusivity based on averaging the parameters of the Guyer-Krumhansl equation according to the observed diffusive time scales. We also found that for such metal matrix syntactic foams, even with knowing the constituents, the contact thermal resistance makes more challenging to provide a prior estimate for the effective thermal conductivity, but this difficulty can be resolved using proper effective thermal diffusivity values.

High temperature and fire properties of sustainable syntactic foam reinforced by end‐of‐life tyre‐derived rubber particles

AbstractThe management of end‐of‐life tyres faces challenges due to insufficient recycling infrastructure and technologies, as well as limited markets for the materials recovered from them. To mitigate this, waste rubber can be upcycled and used as filler material for polymer matrix composites. Before rubber‐reinforced composites can be certified for fire‐prone applications, their thermal and flammability properties must be understood. This research investigates the effect of rubber fillers on the thermal stability, flammability and flame spread characteristics of epoxy matrix syntactic foam. Thermogravimetric analysis, Fourier Transform Infrared spectrometry (FTIR), scanning electron microscopy and attenuated total reflection FTIR spectrometry were employed to elucidate changes in thermal degradation behaviours. The influence of rubber fillers on the flammability of syntactic foam was assessed using the cone calorimeter. The fire reaction properties of rubber‐reinforced foam were affected by the intensity of the incident heat flux. Regardless of the incident heat flux, an increase in rubber content led to higher total heat release. At the lower heat flux of 35 kW/m2, the fire growth rate increased with rubber content, but at the higher heat flux of 50 kW/m2, the fire growth rate decreased as the rubber content increased. Importantly, all rubber‐reinforced syntactic foams achieved a UL94 HB ranking and exhibited reduced flame spread rates compared to the unmodified foam. This study demonstrated the potential for upcycling waste rubber into sustainable engineering products and expanded the knowledge base on fire reaction properties and flame spread characteristics of such hybrid composite materials.

Investigation of the Bending Properties of Ex situ Functional Metal Foams

In each industry, compromises have to be made when choosing materials. Lower-density materials have a significant advantage in the automotive sector, especially due to rising fuel prices, since weight reduction can lower overall fuel consumption. The advantageous properties of metal foams, such as low density, high specific strength, and excellent energy absorption, should be researched and exploited in as many areas and ways as possible. This research aims to perform and evaluate the bending tests of ex situ functional metal foams: aluminum alloy matrix (AlSi7Mg) was used, which was filled with Ø2.5–3.0 mm lightweight expanded clay aggregate particles and surrounded by thin-walled aluminum tubes (AlMgSi0.5) with a wall thickness of 2 mm and an outer diameter of Ø32 mm. Empty tubes, foam-filled tubes (with and without structural epoxy adhesive) and metal matrix syntactic foams were compared based on their flexural strength and energy absorption capacity. Quasi-static three-point bend tests were carried out up to 25 mm deflection. The foam-filled tubes with epoxy adhesive showed an average of 6% increase in flexural strength compared to the foam-filled tubes without adhesive and a 145% increase compared to the metal matrix syntactic foams.

A simulation study on mechanical properties and heat conductivity of magnesium matrix syntactic foams before and after heat treatment

Environmental pollution and energy consumption problems today are seriously affecting people’s lives. In this paper, a new magnesium AZ31B matrix syntactic foam (MMSF) prepared by gravity penetration with hollow alumina microspheres as reinforcement was simulated using ANSYS Workbench for the lightweight design of vehicles. The mechanical properties and heat conductivity of MMSFs prepared by hollow microspheres with different diameters and volume fractions before and after heat treatment were investigated using finite element analysis. The simulation results showed that the MMSF prepared by hollow microspheres with a diameter of 3.6 mm and a volume fraction of 40% had the best mechanical properties and heat conductivity after heat treatment strengthening. Due to low density, high strength, excellent thermal insulation and other advantages, this high-performance MMSF is suitable for making vehicle bodies, which can effectively reduce the overall weight, thus reducing the fuel consumption and pollutant emission caused by driving.

Experimental and numerical analysis of the compression behavior of aluminum syntactic foams reinforced with alumina hollow particles

In this study, analytical, numerical, and experimental methods are used to investigate the compressive behavior of alumina hollow particles reinforced aluminum matrix syntactic foams (AMSF). The representative volume element (RVE) models are generated for different volume fractions to analyze the elastic and elastio-plastic behavior of AMSFs using the FE solver ABAQUS. The geometric feature of the hollow particles is selected close to the actual physical dimensions. The effective elastic properties are estimated using linear homogenization models. For example, the elastic properties predicted using the Mori-Tanaka model are close to the FE-based RVE model data. Later, the macroscopic response (stress-strain data) is determined using the volume-averaging method proposed in the literature. The stress-strain response of the FE model with a 30% volume fraction has shown close agreement with the experimental data. Further, a parametric study is conducted for different particle wall thicknesses. These FE models have great potential in studying the ceramic hollow particles reinforced metal matrix syntactic foams and developing new porous composites under compression loading using RVE-based models.

Dynamic Mechanical Properties of Ceramic Hollow Sphere-Reinforced Aluminum Matrix Syntactic Foams

Dynamic Mechanical Properties of Ceramic Hollow Sphere-Reinforced Aluminum Matrix Syntactic Foams

RECENT PROGRESS ON MAGNESIUM MATRIX SYNTACTIC FOAMS: HOLLOW FILLER SELECTION, PROCESSING TECHNIQUES, AND COMMERCIAL APPLICATIONS

The current scenario focuses on lightweight and better energy-absorbing structural materials for critical engineering applications in aerospace, automobiles, marine, electronic, and implant materials for biomedical industries. The magnesium-based syntactic foams are the preferred choice of material in the same category due to their lightweight, higher plateau strength, better damping characteristics, and excellent energy absorption behavior. Many works were reported based on the polymer and aluminum-based syntactic foams and their developments. However, the rapidly increasing interest in magnesium-based syntactic foams and the adoption of the applications are still at a nascent stage. This proposed review work comprehensively insights the magnesium-based syntactic foam; various hollow filler material usages and summarizes the influence of physical and mechanical behavior on processing routes and future research opportunities for applications.

Dynamic response and residual compressive characteristics of syntactic foams at high and low temperatures

The dynamic response at low and high temperatures and compression after impact of aluminum matrix syntactic foams were studied. There were many cracks in syntactic foams after dynamic compression. The failure behaviors of compression after impact were almost identical to those of quasi-static compression in the late plateau stage and densification stage. The dynamic compressive properties of syntactic foams are greatly affected by the hollow sphere size at low strain rate, but this phenomenon is not remarkable at medium and high strain rates. The compressive strength and plateau stress are insensitive to the strain rate, but the energy absorption increases when increasing the strain rate. The dynamic compressive properties of syntactic foams have low-temperature strengthening and high-temperature softening effects, but the latter no longer changes above 100 ℃. The residual energy absorption is high, which indicates syntactic foams have potential as energy absorbing materials after dynamic damage.

Boosting energy absorption performance of aluminum matrix syntactic foam with carbon coated glass cenospheres

In this study, glass cenospheres are coated with resorcinol/formaldehyde resin in an alkaline solution, and the polymer layer is subsequently transformed into carbon shell by pyrolysis. Because carbon is a strong and light-weight material, the resulting aluminum matrix syntactic foam reinforced with carbon coated glass cenospheres shows low density of 1.35 g cm−3, and high energy absorption capacity of 80.3 MJ m−3. The excellent energy absorption properties are ascribed to the conformal carbon shell that can disperse stress, leading to high compressive strength of the foam. The improved wettability of filler surfaces by liquid metals during pressure infiltration casting is verified using both optical and electron microscopy. In addition, XRD results suggest that no obvious interfacial reactions happen during the preparation of foam.

Compressive deformation behavior of closed-cell aluminium syntactic foam

The present study investigates the compressive deformation behaviour of aluminium matrix syntactic foam. Thecenosphere hollow filler was incorporated into the aluminium matrix to fabricate the syntactic foam using stir casting technique. A compressive test was conducted on the syntactic foam to evaluate their mechanical properties, and the results were compared with the finite element ABAQUS explicit simulation software. The plateau strength and energy absorption capacities of the experimental and numerical results show a deviation of 1.76 and 7.13% respectively. The numerical results are good, in agreement with the obtained experimental results, and beneficial in understanding the compressive behaviour of closed-cell syntactic foam.

Effect of particle size and distribution of hollow spheres on the compressive behavior of aluminum matrix syntactic foams

Effect of particle size and distribution of hollow spheres on the compressive behavior of aluminum matrix syntactic foams

Application of Substructure Techniques to Syntactic Metal Foams in a Finite Element Environment

The presented work focuses on the development of a novel method that can numerically describe the properties of metal matrix syntactic foam (MMSF) with low memory requirements and short computational times without losing the properties of the interior structure. In this paper, we propose a novel method that avoids using the homogenization technique and instead rearranges stiffness matrices and constructs specific substructures to perform the overall construction. The two-dimensional cases are discussed in order to focus on the methodology itself. First, the reductions and structural design with solid mesh structures were performed, and then the model was applied on structures filled with iron hollow spheres. So far, the method has been used to evaluate small deformations to see how suitable the subspace technique is for describing metal foams. Aluminum was used as the matrix material, as it is one of the most common materials for MMSFs. The optimal parameters were searched that resulted in the shortest running time for the given construction. Since in the proposed substructure technique only the displacement values at the boundary points are computed, a back-calculation step for each selected substructure was performed to see the interior deformations in the vicinity of an iron hollow sphere.

A novel approach for in-situ producing Al2O3/aluminum matrix syntactic foam with high specific strength

Low-density foams with high strength are eagerly desired to use as energy absorption and shock isolation systems during transportation. In this work, an Al2O3/aluminum matrix syntactic foam with a density of 1.41 g/cm3 and a compressive strength of 238 MPa was prepared by a novel approach, which specific strength outperforms the most advanced aluminum matrix syntactic foams as reported in the literature. Especially, the hollow Al2O3 spheres were produced by an in-situ reaction of the hollow glass beads in this foam. Moreover, an electric current was first utilized in this new approach, which proved to have a crucial effect on the in-situ reaction, making the hollow glass beads rapidly and completely transform into Al2O3 spheres to improve interface conditions. The approach is believed to provide a favorable strategy to design different metal matrix syntactic foams with improved performance.

On the compressive properties of aluminum and magnesium syntactic foams: Experiment and simulation

The influence of the materials of Al and Mg-based syntactic foams on the compressive behavior was investigated. Two different kinds of foams of cp-Al and cp-Mg in combination with ceramic hollow spheres (Al2O3 or Al2O3/SiO2/mullite) were manufactured by infiltration technique. A full-scale finite element model was established to explain the experimental results and to explore the effect of matrix and hollow sphere properties up to the peak strain. In this full-scale model, the ceramic hollow spheres’ effective elastic and fracture properties were used, determined from compression tests and micromechanical model of single hollow spheres. The finite element model predicted the compression curve with high precision in the investigated deformation range for the highly ductile foams with Al matrix, indicating that fracture becomes the dominant failure mode only near the peak stress. The model of Mg matrix syntactic foams showed that fracture in the early stage of compression did not change the strength of the material; however, it significantly lowered the stiffness in the case of Al2O3 hollow sphere having a diameter of ∼4 mm and thin (150 µm) wall. If significant reactions occurred between the matrix and hollow spheres during manufacturing, the model could estimate the formed complex interface’s effect on the syntactic foams’ strength.