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In this study, the consequence of cell-size, cell-wall-thickness and cell circularity together on the compressive performance of closed-cell aluminum foam was analyzed experimentally and with FEM simultaneously. The closed-cell metal foams (CAFs) with varying cell sizes of 55% porosity were synthesized through stir casting technique. The granular metallic calcium is used as a stabilizing/thickening agent, and TiH2 powder used as a foaming agent. The uniaxial compression tests were performed to investigate the compressive deformation behavior of CAFs. The simulation studies were carried out by taking the assumption similar to experimental constraints. The circular-shaped cells were created in FE half symmetrical model of varying cell sizes (in 2-Dimensional). The cell sizes used in FE models are 1.5 mm, 2.5 mm, 2.8 mm and of 3.5 mm. While in experimental samples, different cell sizes obtained are 1.65 mm, 2.47 mm, 2.88 mm and 3.59 mm. In both of the investigations, it is observed that the energy absorption capacity and plateau strength decrease with an increase in cell sizes or vice versa. A similar effect was also observed with an increase in cell wall thickness. The obtained FE results are acceptable and comparable with the experimental for each cell size model. The deformation mechanism was analyzed using deformed sample images, which were captured during the deformation as well as during the different stages in the FEA models.

In the present study, closed-cell aluminum foams of varying porosities (65–75%) were produced through the stir casting technique using TiH2 (1 wt.%) as a foaming agent. Under the uniaxial compressive loading, the compressive stress-strain responses of these foams were examined. The finite element (FE) models of the foam were elaborated using the ABAQUS FE simulation software and realized via the ABAQUS Explicit solver. Within the test domain, the experimental results were compared with the FE-predicted ones for the same porosities and both yielded similar stress-strain responses. The energy absorption capacity, yield stress, and densification strain values of AFs obtained through FE simulation were in good agreement with the experimental results, while the predicted plateau stress values differed from the latter by no more than 4–5%.

AlSi12Cu1Mg1–SiC-MWCNTs hybrid composite foam (HCFs) of varying relative densities (R.D.) were made through stir casting technique using CaH2 as a foaming agent. Varying wt.% of SiC and multi-wall carbon nanotubes (MWCNTs) were used as reinforcing as well as thickening agents. Uniform distribution of SiC and MWCNTs in the matrix was confirmed by FESEM images and Raman analysis. It was observed that the elastic modulus (E), plastic collapse stress ( σ p c ) , plateau stress ( σ p l ), and energy absorption ( E a b ) of HCFs increase significantly when both (MWCNTs and SiC) were added together. But, when SiC and MWCNTs added individually, the extent of improvement in these properties is relatively low. However, densification strain varies marginally with the variation in reinforcement. Irrespective of reinforcement, the σ p l , the E, and the E a b increased with increment in R.D. The different values also followed the existing relations, when the fraction of cell edge materials varied with R.D., the deformation mechanism was understood from photographs taken during deformation.

Aluminium-SiC-MWCNTs nano-hybrid composites (HCs) were prepared through stir casting technique. The wear rate, coefficient of friction and compressive strength of HCs increase with increasing MWCNTs (multiwalled carbon nanotubes) concentration in aluminum SiC comopsites. But when only MWCNTs are used as reinforcement its strength, wear rate and microhardness values are found to be significantly less than other studied composite materials. Therefore, SiC is used as a secondary reinforcement to enhance the interfacial interaction between MWCNTs and Aluminium. This interaction improved strengthening of matrix due to uniform dispersion of MWCNTs and high mechanical strength of SiC and MWCNTs. When MWCNTs are used separately as reinforcement, it got agglomerated and thus the strength and wear resistance of composite decreased.

The hot deformation behaviour of Al-Si12CulMg1 alloy foam, Al-Si12CulMg1 alloy-single-wall carbon nanotubes (SWNTs), Al-Si12CulMg1-cenospheres, and Al-Si12CulMg1-cenosphere-SWNTs hybrid foams (HFs) were investigated at different test temperatures (25-400°C) and strain rates (10-3-1 s-1) conditions. It is observed that the energy absorption capacity of all the foams decreased with an increased test temperature (TT) whereas it increased with an increase in strain rate. The hybrid foam in which the cenosphere and SWNTs were added together exhibited the highest plateau stress and energy absorption amongst all investigated foams. The strain rate sensitivity and activation energy for each kind of foam was calculated as a function of temperature and strain rate. The activation energy data tells that the deformation mechanism is dominated by vacancy and dislocation diffusion at TT≤200 °C regardless of the type of foam, strain rate and relative density. On the other hand, the deformation mechanism is dominated by dynamic recovery and recrystallization when the TT increase beyond 200°C (TT>200°C). This study further demonstrates the synergistic effect of cenosphere and SWNTs on enhancing the plateau stress and energy absorption of HFs.

Three dimension fire retardant carbon-CNTs hybrid foams for electromagnetic interference (EMI) shielding effectiveness (SE) were fabricated using a polyurethane (PU) template. Phenolic resin with different contents (0.2–2 wt.%) of mutltiwalled carbon nanotubes (MWCNTs) was mixed using a magnetic stirrer for making a homogenous slurry and then PU foam was impregnated in this slurry followed by carbonization at 1000 °C. The foams were characterized for their morphological, structural, mechanical, EMI shielding, and fire-retardant properties. The total EMI shielding effectiveness (SE) of -57.2 dB was achieved for the carbon foam containing 1 wt.% MWCNTs in the frequency range of 8.2–12.4 GHz. Moreover, the addition of MWCNTs into phenolic resin also enhanced the compressive strength (6.5 MPa), thermal stability and fire retardant performance of carbon-CNTs hybrid foams. The multifunctional carbon-CNTs hybrid foams demonstrate that they are outstanding materials with potential applications in EMI shielding and thermal management for defense and aerospace sectors.

The effect of relative density (RD) and shape of the space holder on microstructural characteristics and compressive behavior of open-cell aluminum foams (OAFs) have been studied. OAFs with tailored porous morphologies (50–81%) were successfully prepared through space holder technique using spherical shape carbamide and cubic shape sucrose space holders in various amounts. Al powder and space holders were mixed with 2 wt% of polyvinyl alcohol (PVA) binder solution, compacted at 300 MPa and finally sintered at 650 °C for 3 h. It was observed that the microstructural characteristics of OAFs varied in accordance with the shapes of space holders. The results reveal that the OAFs prepared with carbamide show smooth microstructure, higher plateau stress (~3 times), higher energy absorption (~3 times) and higher Young's modulus, but lower densification strain, compared to the OAFs prepared with sucrose. The Young's modulus, plateau stress, and energy absorption of OAFs, follow the power-law relationship as a function of its RD irrespective of the shape of space holders. The thermal conductivity of Al-carb and Al-suc OAFs are noted to be not much in variation irrespective of the shape of the pores.

In the present study, single-walled carbon nanotubes (SWNTs) and cenosphere reinforced closed cell hybrid aluminium foams (HAFs) of varying relative densities were produced, and their compressive deformation behaviour at different strain rates have been examined. The addition of SWNTs leads to a significant increase in plateau stress, plastic collapse stress, and energy absorption. This may be due to higher dislocation density and finer inter-SWNT spacing. The Raman spectra of HAFs showed the uniform distribution of SWNTs in the cell wall region. However, the effect of quasi-static strain rates (10−3 to 10 s−1) on the compressive deformation response is marginal. While the influences of higher strain rate ranges (10−3 to 1500 s−1) are considerably higher than the quasi-static strain rate range. The strain rate sensitivity of these foams is much less than unity (~0.0088-0.0314), indicating the brittle nature of foam deformation. The plastic collapse, plateau stress, and energy absorption of HAFs increase significantly with an increase in relative density. Interestingly, it is observed that both plateau stress and energy absorption follow power-law relation with relative density, and densification strain follows a linear relation with relative density irrespective of strain rate and foam material. It is further noted that the strain rate sensitivity of HAFs increases marginally with relative density. The deformation mechanism of HAFs has been examined using the digital photographs captured during the uniaxial compression test and the SEM, TEM images of deformed specimens.

In the present work, a novel approach was used for the synthesis of ultra-light closed cell Al-hybrid foam reinforced with functionalized Multiwall carbon nanotubes (MWCNTs) and silicon carbide (SiC) particles through stir casting technique. In this work, up to 93%, porous hybrid foam with uniform cell size were successfully prepared. For uniform dispersion of MWCNTs within the matrix, first MWCNTs were functionalized in HNO3 solvent with magnetic stirring followed by partial ball milling with Al powder and SiC particles. Obtained results show that the plateau stress and energy absorption capacity of prepared ultra-light foams are excellent.

K. S. Verma, D. Muchhala, S. Panthi, and D. P. Mondal, “Experimental and numerical study of compressive deformation behavior of closed-cell aluminum foam,” Strength Mater., 52, 451–457 (2020), https://doi.org/10.1007/s11223-020-00197-4 the authors’ affiliations should read

High-temperature deformation behavior of LM13 aluminium alloy foam and LM13-silicon carbide (SiC)-multiwall carbon nanotube (MWCNTs) hybrid composite foams (HCFs) was studied and compared with that of LM13-SiC and LM13-MWCNTs composite foams at a temperature range of 25 °C–400 °C and strain rate ranging from 0.001 to 1 s−1. It is noted that the plateau stress and energy absorption decreased with the increasing temperature but increased with increasing the strain rate. Irrespective of kind of foams the combined effect of temperature and strain rate were investigated and the activation energy was determined for each type of foams as a function of temperature and strain rate. The cell walls collapse and microstructural changes during hot deformation were also examined. The hybrid composite foam exhibited the highest plateau stress, modulus, and energy absorption, whereas the alloy foams are softer foam with the lowest plateau stress, modulus, and energy absorption. At temperature 200 °C the deformation is controlled by dynamic recovery and recrystallization.

Aluminium hybrid foam (HF) core sandwich structures with carbon fiber-cold setting resin as face sheets have been made. The flexural properties and energy absorption of these sandwich structures have been analyzed through three-point bending (3 PB) test. It is found that with the use of a double-layer carbon fiber sheet, the flexural load carrying capacity of the sandwich structure increases up to eight times as compared to that of bare foam (BF) structure. Whereas, the bending stiffness of the structure is nine times to that of BFs and energy absorption is 58% more than that of BF. It is also found that with the increase in foam core thickness the flexural load carrying capacity, bending stiffness and energy absorption capacity of the sandwich structure increases significantly. The specific strength and bending stiffness increase as compared to that of face sheet due to the addition of foam at the core. The deformation behavior of different sandwich structures was analyzed to investigate the different modes of failure during bending.

In present investigation Ti6Al2Co foams were prepared at different sintering temperatures (1000–1200 °C) using varying amount of space holder contents (40–70%). The prepared foams were characterized in terms of microstructural and mechanical properties. It was found that increase of sintering temperature increased the relative density (RD) and reduced the interparticle gap. The increase of sintering temperature increased the strength, modulus, energy absorbing capacity and microhardness of the samples. The plateau stress and Young’s modulus of prepared foams were found to follow the power law relationship and the constants involved in these equations were found to be in good agreement with the reported values. Further, increment in space holder content, reduced the RD, plateau stress, energy absorption, modulus and hardness of the Ti6Al2Co foams.

Al-Cenosphere-SWCNTs closed cell hybrid foams (HFs) of varying relative densities ( ρ r d ) were synthesized through stir casting technique using TiH2 (0.6 wt % of alloy) as a foaming agent, processed SWCNTs (0, 0.1, 0.2, 0.3 and 0.4 wt %) and cenosphere (4.25 wt % or 15 vol %) as thickening agent. Cenosphere particles provided micro-porosity within the cell wall and its shells act as reinforcement. It was noted that the addition of SWCNTs and Cenosphere improved the mechanical properties such as elastic modulus ( E f ) , plastic collapse stress ( σ p c ) , plateau stress ( σ p l ) and, energy absorption capabilities ( E a b ) of HFs. In HFs these properties increases with increase in SWCNTs up to 0.3 wt % and a further increase in SWCNTs content leads to the reduction of these properties of HFs. It is interestingly observed that the densification strain ( e D ) for a constant ρ r d is almost invariant to the SWCNTs content. The mechanical properties of the AFs and HFs foamsareempirically simulated and also compared with standard existing models for the different SWCNTs contents and ρ r d . The deformation mechanism has been examined during compression test.