Automated continuous production line of parts made of metallic foams

The paper presents an automated continuous production line (7 m × 1.5 m × 1 m) of high-quality metallic foams using a powder metallurgical method. This continuous production line was used to obtain metal foam parts and/or components by heating the foamable precursor material at melting temperatures close to the temperature of the metallic matrix and cooling the formed liquid metallic foam (in liquid state), which then results in a solid closed-cell metallic foam. This automated continuous production line is composed of a continuous foaming furnace, a cooling sector and a robotic system. This installation has enabled a technological breakthrough with many improvements solving some technical problems and eliminating the risks and dangers related to the safety of workers due to the high temperatures involved in this process. The whole process becomes automatic without any need for human intervention.publishe

Bending performance evaluation of aluminium alloy tubes filled with different cellular metal cores

A comprehensive bending performance and energy absorption capability of aluminium alloy tubes filled with different cost-effective cellular metal cores were experimentally evaluated for the first time. The following cellular metal cores were evaluated: i) Advanced Pore Morphology (APM) foam, ii) hybrid APM foam and iii) Metallic Hollow Sphere Structures (MHSS). The results have been compared also with the performance of aluminium alloy tubes filled with (ex-situ and in-situ) closed-cell aluminium alloy foam. The three-point bending tests have been performed at two loading rates (quasi-static and dynamic) and supported by infrared thermography to evaluate the deformation mechanism, damage progress and failure modes. A thorough heat treatment sensitivity (due to the fabrication procedures of composite structures) study on the aluminium tubes has been performed as well. The results show that a reliable and predictable mechanical behaviour and failure can be achieved with proper combination of tubes and cellular metal core. A low scatter of bending properties and energy absorption capability has been observed. The hybrid APM and the ex-situ foam filled tubes achieved the highest peak load. However, they also exhibit a rapid load drop and abrupt failure once the structure has reached the peak load. The APM, MHSS and in-situ foam filled tubes show more ductile behaviour with a predictable failure mode.publishe

Crush performance of multifunctional hybrid foams based on an aluminium alloy open-cell foam skeleton

Multifunctional hybrid foams were developed and tested by combining aluminium alloy open-cell (OC) foam specimens with polymers, epoxy resin and silicone rubber. The rectangular OC foam specimens were impregnated with polymer, completely filling the voids. The aim of this work was to evaluate the effect of the polymer presence in the voids of aluminium alloy OC foam specimens (varying their size, e.g. height to width ratio) on the crush performance of the resulting hybrid foams. Quasi-static and dynamic uniaxial compressive tests and infrared thermography were used to compare the behaviour of hybrid foams with conventional (unfilled) OC foam specimens. Results show an improvement of the compressive strength and energy absorption capacity of hybrid foams, especially when infiltrated with epoxy resin. The results show that the epoxy leads to higher capacity of specific energy absorption of the hybrid foams, while silicone leads to lower capacity of specific energy absorption in comparison to the OC foam specimens. The high energy absorption values of OC foams embedded with silicone are not enough to compensate for the mass increase due to the silicone filler. The use of the polymers as a void filler changes the typical layer-wise collapse mechanism of the OC foam. The silicone rubber causes a non-symmetric deformation, being much more complex and unstable in the case of the longer hybrid foams, which deform by buckling (lateral instability). The epoxy resin enforces a symmetric deformation by folding in the middle of the hybrid foams.publishe

Mechanical, thermal, and acoustic properties of aluminum foams impregnated with epoxy/graphene oxide nanocomposites

Hybrid structures with epoxy embedded in open-cell aluminum foam were developed by combining open-cell aluminum foam specimens with unreinforced and reinforced epoxy resin using graphene oxide. These new hybrid structures were fabricated by infiltrating an open-cell aluminum foam specimen with pure epoxy or mixtures of epoxy and graphene oxide, completely filling the pores. The effects of graphene oxide on the mechanical, thermal, and acoustic performance of epoxy/graphene oxide-based nanocomposites are reported. Mechanical compression analysis was conducted through quasi-static uniaxial compression tests at two loading rates (0.1 mm/s and 1 mm/s). Results show that the thermal stability and the sound absorption coefficient of the hybrid structures were improved by the incorporation of the graphene oxide within the epoxy matrix. However, the incorporation of the graphene oxide into the epoxy matrix can create voids inside the epoxy resin, leading to a decrease of the compressive strength of the hybrid structures, thus no significant increase in the energy absorption capability was observed.publishe

Shear modulus of conventional and auxetic open-cell foam

This work analyses shear moduli of conventional and auxetic open-cell polymer foams. Shear moduli are i) measured directly and ii) calculated by applying elasticity theory for isotropic solid materials, using Young's moduli and Poisson's ratios from compression tests. Zero and negative Poisson's ratio foams are fabricated from conventional foams using a thermo-mechanical process. Fabricated and conventional foams are compression tested in three orthogonal directions, up to densification at ~60% compression, with full-field strain measurements obtained using Digital Image Correlation. Compression testing is followed by shear testing. The measured shear moduli vary from 16±7 kPa for negative Poisson's ratio foams to 38±2 kPa for zero Poisson's ratio foams, with conventional foams in between with a mean value of 32±8 kPa. The calculated shear moduli are typically lower than the measured values. The results suggest that the application of elasticity theory to calculate the low strain shear modulus of open-cell foam from Young's modulus and Poisson's ratio measured in compression tests is appropriate if the foam is isotropic

Characterization and physical properties of aluminium foam−polydimethylsiloxane nanocomposite hybrid structures

This article reports on the fabrication and characterisation of hybrid structures prepared by impregnating an open-cell aluminum foam with polydimethylsiloxane (PDMS) or PDMS reinforced with graphene oxide, GO (PDMS nanocomposite). The effect of the PDMS and the GO on the mechanical, thermal, acoustic absorption and fire retardancy properties of the resulting hybrid structures were evaluated and compared to the individual components (PDMS, PDMS nanocomposite, open-cell aluminium foams). Results demonstrate that the use of the PDMS cured at 65 °C, as an void filler of the open-cell aluminium foams, changes mechanical and deformation performance, from a rubbery to brittle behaviour, however attaining a higher level of strength (quasi-static: ∼5 MPa; dynamic: > 15 MPa) in the resulting hybrid structures. This change is due to the low chain mobility of the polymer and effective adhesion with struts of the open-cell aluminium foams. Furthermore, these hybrid structures are extremely sensitive to strain-rate testing, exhibiting a maximum compressive stress increase of more than 300 % and 200 %, respectively. The presence of the GO within the PDMS improves significantly the non-flammability of the hybrid structures and increases the sound absorption coefficient.publishe

Compressive behaviour of closed-cell aluminium foam at different strain rates

Closed-cell aluminium foams were fabricated and characterised at different strain rates. Quasi-static and high strain rate experimental compression testing was performed using a universal servo-hydraulic testing machine and powder gun. The experimental results show a large influence of strain rate hardening on mechanical properties, which contributes to significant quasi-linear enhancement of energy absorption capabilities at high strain rates. The results of experimental testing were further used for the determination of critical deformation velocities and validation of the proposed computational model. A simple computational model with homogenised crushable foam material model shows good correlation between the experimental and computational results at analysed strain rates. The computational model offers efficient (simple, fast and accurate) analysis of high strain rate deformation behaviour of a closed-cell aluminium foam at different loading velocities.publishe

Evaluation of thermal and mechanical filler gas influence on honeycomb structure behavior

In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions