Search Results (77)

Aluminium alloy foams have been widely used due to their excellent strength-to-weight ratio, low density, and outstanding properties such as high energy absorption and effective noise and heat insulation. In this study, aluminium machining chips have been used for foam production as a potential recycling method. The process has involved solution heat treatment followed by artificial ageing. Researchers have been analysing the microhardness of both the foam and the bulk material, as well as examining their microstructures. The maximum microhardness value of the bulk material has been found to be 158 ± 2 HV1 at an ageing temperature of 175 ± 1 °C for 2 ± 0.02 h. For the foams, the highest microhardness of 150 ± 2 HV1 has been achieved after ageing at 150 ± 1 °C for 9 ± 0.02 h. Experimental planning has been carried out using Design Expert software. The optimisation process has identified 150 ± 1 °C for 2 ± 0.02 h as the optimum condition for artificial ageing. Full article

This study explores how production technology influences spray-applied rigid polyurethane (PUR) foam insulation’s cryogenic performance. In cryogenic applications such as liquid gas storage, insulation must minimise heat transfer and resist moisture ingress under severe thermal gradients. Experimental aluminium vessels were insulated with PUR foam of varying thicknesses and surface conditions—rough, machined smooth, and with a urea-based protective coating—and then tested using dynamic boil-off of liquid nitrogen (LN₂). Foam properties, including adhesion, mechanical strength, thermal expansion, thermal conductivity, and closed-cell content, were evaluated. The results revealed that thicker insulation reduced both effective thermal conductivity and moisture uptake. Although the urea-coated vessel showed minimal water absorption, the coating increased overall thermal conductivity due to its heat conduction and condensation behaviour. Moisture was primarily absorbed near the foam surface, and no cumulative effects were observed during repeated tests. The effective thermal conductivity was determined by interpolating boil-off data, confirming that insulation performance strongly depends on thickness, surface condition, and environmental humidity. These findings provide valuable guidance for the design and application of PUR foam insulation in cryogenic environments. Full article

Epidemiological analysis has revealed key insights into the frequency, severity, and circumstances surrounding subway-to-pedestrian incidents; however, there remains a lack of available impact test data specific to this impact type that can be used in modelling and countermeasure design studies. To address this gap, nine controlled impact tests were conducted using a cylindrical headform to derive force–penetration relationships for foam, as well as foam encased in 1 mm aluminium or 3 mm ABS shells. These relationships were validated in MADYMO multibody simulations. Building on a previous multibody computational study of subway-to-pedestrian collisions this research evaluates three passive countermeasure designs using a reduced simulation test matrix: three impact velocities (8, 10, and 12 m/s) and a trough depth of 0.75 m. In subway collisions, due to the essential rigidity of a subway front relative to a pedestrian, it is the pedestrian stiffness characteristics that primarily dictate the contact dynamics, as opposed to a combined effective stiffness. However, the introduction of energy-absorbing countermeasures alters this interaction. Results indicate that modular energy-absorbing panels attached to the train front significantly reduced the Head Injury Criterion (HIC) (by 90%) in the primary impact and pedestrian-to-wheel contact risk (by 58%), with greater effectiveness when a larger frontal area was covered. However, reducing primary impact severity alone did not substantially lower total fatal injury risk. A rail-guard design, used in combination with frontal panels, reduced secondary impact severity and led to the largest overall reduction in fatal injuries. This improvement came with an expected increase in hospitalisation-level outcomes, such as limb trauma, reflecting a shift from fatal to survivable injuries. These findings demonstrate that meaningful reductions in fatalities are achievable, even with just 0.5 m of available space on the train front. While further development is needed, this study supports the conclusion that subway-to-pedestrian fatalities are preventable. Full article

The energy-absorbing capacity and friction phenomena of different closed-cell aluminium foam-filled Al tube types are investigated through experimental compression tests. Concerning the kind of investigation, free, radial-constrained and friction tests occurred. The radial-constrained compression test results confirm that the process requires significantly more compression energy than without the constrain. Pushing away different pre-compressed foams inside the aluminium tube, the static and kinematic frictional resistances can be determined and the energy required to move them can be calculated. Knowing the value of the energy required for the frictional resistance, we can obtain how much of the energy surplus in radially inhibited compression is caused by the friction phenomena. The main goal present study is to reveal the magnitude of friction between the foam and the wall of the tube during the radially constrained test. The investigation used 0.4 and 0.7 g/cm³ density closed-cell aluminium foam whilst a compressive test was applied where the force–displacement data were recorded to calculate the absorbed energy due to friction. Considering the results of the test, it can be stated that 18% of the invested energy was used to overcome friction in the case of lighter foam and almost 23% with 0.7 g/cm³ foam during the radial-constrained test. Full article

This study analyses the heat transfer performance of metal foam heat exchangers through experimental measurements. Using counter-gravity infiltration casting, open-cell aluminium foam elements were manufactured to embed a copper tube for internal mass flow containment. Heat transfer experiments were conducted under natural and forced convection conditions, with the airflow controlled in a wind tunnel. A stream of warm water within the internal foam component served as the heat source, transferring thermal energy to the surrounding air flowing through the external foam component of the heat exchanger. The results showed a significantly enhanced heat transfer performance with aluminium foam compared to a single copper tube. Thermal resistance models were developed to elucidate the heat transfer mechanisms, highlighting the effectiveness of air-cooled metal foam heat exchangers. These findings underscore the potential of metal foam heat exchangers as cost-effective alternatives for various thermal management applications. Full article

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. Full article

This paper proposes an innovative multi-material approach for introducing auxetic behaviour to syntactic foams (SFs). By carefully designing the size, shape, and orientation of the SFs, auxetic deformation behaviour was induced. Re-entrant hexagon-shaped SF elements were fabricated using expanded perlite (EP) particles and a plaster of Paris slurry first. Then, an auxetic pattern of these SF elements was arranged within a stainless-steel casting box. The empty spaces between the SF elements were filled with molten aluminium alloy (A356) using the counter-gravity infiltration casting technique. The cast auxetic composite had a bulk density of 1.52 g/cm³. The cast composite was then compressed under quasi-static loading to characterise its deformation behaviour and to determine the mechanical properties, especially the Poisson’s ratio. The cast composite deformation was auxetic with a Poisson’s ratio of −1.04. Finite Element (FE) simulations were conducted to understand the deformation mechanism better and provide means for further optimisation of the geometry. Full article

The paper compares and evaluates the influence of the presence of perforations on the sound absorption coefficient (SAC) of a negative stiffness metamaterial based on a foamed ceramic geopolymer. Chemical–physical, microstructural, dynamic–mechanical, and sound characterisations are presented. A rigid, lightweight geopolymeric porous material has been prepared using an inorganic/organic monomeric mixture containing oligomeric sialates and siloxanes foamed with aluminium powder. This process results in an amorphous rigid light foam with an apparent 180 Kg/m³ density and a 78% open-pore. The viscoelastic characterisation by dynamic mechanical analysis (DMA) carried out from 10⁻³ to 10³ Hz indicates the behaviour of a mechanical metamaterial with negative stiffness enabling ultrahigh energy absorption at straining frequencies from 300 to 1000 Hz. The material loss factor (the ratio of dissipative/elastic shear moduli) is about 0.03 (essentially elastic behaviour) for frequencies up to 200 Hz to suddenly increase up to a value of six at 1000 Hz (highly dissipative behaviour). The corresponding storage and loss moduli were 8.2 MPa and 20 MPa, respectively. Impedance tube acoustic absorption measurements on perforated and unperforated specimens highlighted the role of perforation-resonant cavities in enhancing sound absorption efficiency, particularly within the specified frequency band where the mass of the negative stiffness foamed geopolymer matrix magnifies the dissipation effect. In the limits of a still exploratory and comparative study, we aimed to verify the technological transfer potentiality of using architected metamaterials in sustainable building practices. Full article

Metal foams are newly developed engineered materials with attractive mechanical properties such as lightness, high resistance-to-weight ratio, and insulation capabilities. Lately, applications of these technologies have demonstrated the possibility of obtaining high-performance sandwich panels with steel skins and metal foam core, with potential applications across various fields. Within this framework, this work aims to assess the response of sandwich panels made of steel and aluminium foam to develop a new system of dry-assembled composite floors. The present study investigates a novel screwed steel–aluminium foam–steel (SSAFS) sandwich panel. This paper mainly describes and discusses the results of experimental tests devoted to evaluating the structural performance, mechanical properties, and suitability for practical applications of SSAFS. The fabrication process and the detailing of the steel skins and aluminium foam core assembly are also described. The results from the experimental tests revealed the potentialities of using SSAFS sandwich panels in terms of strength and stiffness, thus making them suitable for lightweight structural systems. Full article

Thermal management devices such as heat exchangers and heat pipes are integral to safe and efficient performance in multiple engineering applications, including lithium-ion batteries, electric vehicles, electronics, and renewable energy. However, the functional designs of these devices have until now been created around conventional manufacturing constraints, and thermal performance has plateaued as a result. While 3D printing offers the design freedom to address these limitations, there has been a notable lack in high thermal conductivity materials beyond aluminium alloys. Recently, the 3D printing of pure copper to sufficiently high densities has finally taken off, due to the emergence of commercial-grade printers which are now equipped with 1 kW high-power lasers or short-wavelength lasers. Although the capabilities of these new systems appear ideal for processing pure copper as a bulk material, the performance of advanced thermal management devices are strongly dependent on topology-optimised filigree structures, which can require a very different processing window. Hence, this article presents a broad overview of the state-of-the-art in various additive manufacturing technologies used to fabricate pure copper functional filigree geometries comprising thin walls, lattice structures, and porous foams, and identifies opportunities for future developments in the 3D printing of pure copper for advanced thermal management devices. Full article

To investigate the fluid flow characteristics of conventional Ceramic Foam Filters (CFFs) of grades 30 and 50, a 2D macro-scale geometry was generated by converting pixel grid images of the filters into vector format images. The flow behaviour through the filter channels was then numerically modelled using the Stocks equation within the Creeping Flow interface of COMSOL Multiphysics^®. Through modelling, the average interstitial velocity was estimated and found to be higher than the corresponding value obtained from the Dupuit–Forchheimer equation. The discrepancy obtained suggested that the flow behaviour within the filter channels differed from that based on the simplified assumptions of the equation. The porosity and permeability of the CFFs were evaluated during the post-processing stage using surface integration and user-defined equations. The experimentally determined porosity closely matched the values obtained from the simulation model, demonstrating the reliability of the numerical approach. However, the permeability values from the simulation of CFFs of grades 30 and 50 were higher than those obtained experimentally. This discrepancy can be attributed to the larger channels in the generated geometrical pattern compared to the original CFF structure. The present findings highlight the effectiveness of the proposed methodology in developing a representative macro-scale geometry for CFFs and in simulating fluid flow behaviour. Full article

This experimental work presents the results of measurements of thermal conductivity λ and convection heat transfer coefficient h on regular structure PLA and aluminium foams with low density ratio (~0.15), carried out with a TCP (thermal conductivity probe), built by the authors’ laboratory. Measurements were performed with two fluids, water and air: pure fluids, and samples with the PLA and aluminium foams immersed in both fluids have been tested. Four temperatures (10, 20, 30, 40 °C) and various temperature differences during the tests ΔT (between 0.35 and 9 °C) were applied. Also, tests in water mixed with 0.5% of a gel (agar agar) have been run in order to increase the water viscosity and to avoid convection starting. For these tests, at the end of the heating, the temperature of the probe reaches steady-state values, when all the thermal power supplied by the probe is transferred to the cooled cell wall; thermal conductivity was also evaluated through the guarded hot ring (GHR) method. A difference was found between the results of λ in steady-state and transient regimes, likely due to the difference of the sample volume interested by heating during the tests. Also, the effect of the temperature difference ΔT on the behaviour of the pure fluid and foams was outlined. The mutual effect of thermal conductivity and free convection heat transfer results in being extremely important to describe the behaviour of such kinds of composites when they are used to increase or to reduce the heat transfer, as heat conductors or insulators. Very few works are present in the literature about this subject, above all, ones regarding low-density regular structures. Full article

The aim of this study was to investigate the potential application of metal foams in shell-tube recuperators. A356 aluminium foam was cast around the internal and external surfaces of a thin-walled copper tube to enhance heat transfer between separated water streams at different temperatures. The results demonstrated that the aluminium foam drastically increased heat transfer efficiency due to its large volumetric surface area and high thermal conductivity. In the shell-tube foam recuperators, a maximum heat transfer efficiency of 48.1% was observed, compared to only 12.2% for a single copper tube without metal foam. The pressure drop across the external foam increased with the flow rate, from an average value of 1.19 kPa at 1.0 L/min to 7.36 kPa at 3.0 L/min. These findings suggest that metal foams have great potential for use in shell-tube recuperators, which could significantly improve the efficiency of heat transfer in various industrial and engineering applications. Full article

The present research concerns fabrication of Al-4.3wt.%Cu metal syntactic foams using expanded perlite particles (EPPs). A gas pressure infiltration technique was employed to fabricate the aluminium syntactic foams under different infiltration temperatures and pressures. Ambient air pressure and 750 °C were identified as the favoured processing conditions for full infiltration of the melt. The average density and EP volume percentage of the fabricated foams were measured to be about 1.55 g/cm³ and 50.3%, respectively. Melt infiltration is believed to be mainly controlled by the breakage of the aluminium oxide layer on the melt surface and melt viscosity. Preferential infiltration of the melt between the mould wall and the EP particles bed complemented by radial melt infiltration toward the centre of the samples was identified. The effects of EP particles on growth of the nucleated primary α-aluminium phase were discussed. XRD and EDS analyses suggested some chemical reactions at the interface of EPPs with the molten aluminium. T6 heat treatment in the ambient atmosphere improved the average compressive tensile strength, plateau stress, and absorption capacity of the syntactic foams by more than 100%. Uniform deformation and similar densification strains (about 40%) of the as-fabricated and heat-treated syntactic foams during the compression test suggested uniform distribution of EP particles and metallic struts in the aluminium alloy matrix. Full article

The choice of foaming agent and its mass fraction significantly affect the size and number of metal foam cells. The powder metallurgy process was used to produce aluminium foams with the addition of various foaming agents: titanium hydride (TiH₂) and calcium carbonate (CaCO₃). TiH₂ was added in an amount of 0.4 wt.%, while the quantity of CaCO₃ varied between 3 and 5 wt.%. The produced foams, with approximately the same degree of porosity, were scanned using a non-destructive computed tomography method. The number, size, equivalent diameter, sphericity, and compactness of cells were analysed on the obtained three-dimensional models. The results showed that foams foamed with TiH₂ have much larger cells compared to CaCO₃ agent. By considering the influence of CaCO₃ fraction on the morphology of aluminium foam, it follows that a smaller quantity of CaCO₃ (3 wt.%) provides a macrostructure with smaller cells. Samples with five wt.% CaCO₃ contain slightly larger cells but are still much smaller than foams with TiH₂ foaming agent at the same degree of porosity. The sphericity and compactness indicate that TiH₂ foaming agent forms cells of a more regular shape compared to CaCO₃ agent. Full article