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Open-cell and closed-cell metal foams have been reinforced with different kinds of micro- and nano-sized reinforcements to enhance their mechanical properties of the metallic matrix. The idea behind this is that the reinforcement will strengthen the matrix of the cell edges and cell walls and provide high strength and stiffness. This manuscript provides an updated overview of the different manufacturing processes of composite and nanocomposite metal foams.

In the present study, we analyze the nonlinear forced vibration of thin-walled metal foam cylindrical shells reinforced with functionally graded graphene platelets. Attention is focused on the 1:1:1:2 internal resonances, which is detected to exist in this novel nanocomposite structure. Three kinds of porosity distribution and different kinds of graphene platelet distribution are considered. The equations of motion and the compatibility equation are deduced according to the Donnell’s nonlinear shell theory. The stress function is introduced, and then, the four-degree-of-freedom nonlinear ordinary differential equations (ODEs) are obtained via the Galerkin method. The numerical analysis of nonlinear forced vibration responses is presented by using the pseudo-arclength continuation technique. The present results are validated by comparison with those in existing literature for special cases. Results demonstrate that the amplitude–frequency relations of the system are very complex due to the 1:1:1:2 internal resonances. Porosity distribution and graphene platelet (GPL) distribution influence obviously the nonlinear behavior of the shells. We also found that the inclusion of graphene platelets in the shells weakens the nonlinear coupling effect. Moreover, the effects of the porosity coefficient and GPL weight fraction on the nonlinear dynamical response are strongly related to the porosity distribution as well as graphene platelet distribution.

Closed-cell aluminum foams have many excellent properties, such as low density, high specific strength, great energy absorption, good sound absorption, electromagnetic shielding, heat and flame insulation, etc. As a new kind of material, closed-cell aluminum foams have been used in lightweight structures, traffic collision protections, sound absorption walls, building decorations, and many other places. In this paper, the recent progress of closed-cell aluminum foams, on fabrication techniques, including the melt foaming method, gas injection foaming method, and powder metallurgy foaming method, and on processing techniques, including powder metallurgy foaming process, two-step foaming process, cast foaming process, gas injection foaming process, mold pressing process, and integral foaming process, are summarized. Properties and applications of closed-cell aluminum foams are discussed based on the mechanical properties and physical properties separately. Special focuses are made on the newly developed cast-forming process for complex 3D parts and the improvement of mechanical properties by the development of small pore size foam fabrication and modification of cell wall microstructures.

A numerical assessment of the heat transfer efficacy of a solar air heater (SAH) was carried out. The SAH is supplied with a porous metal foam layer to improve thermal mixing. Both the local thermal non-equilibrium (LTNE) and Darcy-extended Forchheimer (DEF) models were employed to forecast fluid and thermal transport within the partly filled SAH channel. The analysis was performed for various values of dimensionless foam layer lengths ( S = 0 - 1 ), pore densities ( ω = 10 - 40 PPI ), and Reynolds numbers ( R e = 4000 - 1 6 , 000 ) at a fixed value of layer thickness ( H f = 0.6 ). Based on the position of the porous layer, three distinct arrangements, marked as Case 1, Case 2, and Case 3, were explored. Regarding the parameters examined, the findings indicate a definite improvement in the average Nusselt number ( Nu ), but unfortunately, the friction factor also increases unfavorably. By reducing the length of the porous layer, a reasonable reduction in heat transfer rate and a significant decrease in pressure drop were noticed. The results showed about 26.64%, 48.73%, and 70.74% reductions in pressure drop by reducing the dimensionless foam length from 1 to 0.25, 0.5, and 0.75 respectively for ω = 10 at R e = 16 , 000 . On the other side, there are only about 11.05%, 23.11%, and 40.78% reductions in Nu . The exhaustive analysis of the thermal performance of SAH was conducted using the thermal performance factor (TPF), which considers the trade-off between the SAH channel’s potential for improved heat transmission and its cost for pressure loss. The TPF may reach a maximum of 2.82 compared to the empty channel when the metal foam layer is inserted with S = 1 , for ω = 10 , and R e = 16 , 000 .

This study focuses on the fabrication and characterization of aluminum foam reinforced with nanostructured γ-Al2O3, utilizing AA5083 plates. The fabrication process involved the integration of TiH2 foaming agent particles and reinforcing nanoparticles via the friction stir process (FSP), resulting in the creation of precursor specimens. Subsequently, a separate foaming stage was conducted within a laboratory furnace. The integration of these particles was achieved through the machining of parallel grooves in a single aluminum plate. The initial phase of the experimental study focused on investigating the effect of varying amounts of the foaming agent. Large-scale foams were then produced, achieving a medium porosity of 70%. Electro-discharge machining was employed to prepare specimens for compression testing to analyze their stress–strain response. The results revealed a plateau stress of 27 MPa, a relative Young’s modulus of 4.44 × 10−3, and an energy absorption close to 17 MJ/m3 at 50% strain. Significantly enhanced plateau stress was observed in the manufactured reinforced aluminum foam compared to similar foams produced through conventional methods.

Porous copper (Cu), with varying porosities, has been made using carbamide as a space holder through the powder metallurgy route. Two shapes of carbamide particles were used, (i) needlelike and (ii) spherical, in order to investigate the effect of the space holder shape on the pore structure and mechanical properties of porous Cu. The compressive deformation behavior of porous Cu was studied under a compression test. The pores’ structural characteristics and mechanical properties of the porous Cu varied significantly with the shape of the space holder. Although the effect of the space holder shape on the porosity was not regular, the effect on the mechanical properties was regular. The stress increased monotonically with the increase in the strain, and strain hardening occurred at the plastic yield stage. The elastic modulus and yield strength followed the power law, with the relative density irrespective of the space holder shape. The empirical constants associated with different empirically developed power law relations were different, according to the shape of space holder. A quantitative relationship between the elastic modulus and yield strength and the spacer content was obtained to control the mechanical properties of the present porous Cu or other porous metals and metal foams using the well-known space holder method.

The present work pays attention to the primary resonance of axially moving graphene-reinforced mental foam (GPLRMF) cylindrical shells with geometric imperfection. Porosities and graphene platelets (GPLs) are uniformly or non-uniformly distributed along the thickness direction of the cylindrical shell. Considering the influences of initial geometric imperfection and axial velocity, the equivalent elastic modulus is calculated by Halpin–Tsai model, and the equivalent density and Poisson’s ratio are described by the mixture rule. Using the energy principle, the nonlinear equations of motion are derived. Considering two different boundary conditions, the nonlinear primary resonance response is obtained using the modified Lindstedt Poincare (MLP) method. The results indicate that the MLP method can effectively overcome the limitation of traditional perturbation method. In the end, we study the effects of the GPLs distribution patterns, GPLs weight fraction, the porosity coefficient, axial velocity, initial geometric imperfection, and the prestressing force on the resonance problems. It can be found that the presence of initial geometric imperfection can alter the frequency response curve from the characteristics of the hard spring to the soft spring.

In order to reduce the weight of integrated metal foam skeleton under the double constraints of target thermal and structural reliability indexes, this work proposes a three-dimensional (3D) thermal-structural reliability-based topology optimization (RBTO) method, in which the position uncertainty of the multi-structural-thermal loads is considered. The double reliability index constraints in RBTO are decoupled to a sequence of deterministic topology optimization (DTO) and inverse reliability assessment equivalently, based on performance measure approach (PMA). The inverse most probable failure points (IMPP) required by decoupling sequence are searched by the method of moving components. And the sensitivity required in skeleton topology update and IMPP searching are both quickly evaluated by complete analytical expressions using the adjoint method. Results show that 10.12–16.06% additional weight is introduced by RBTO compared to DTO when reliability index increases from 2 to 3, and the rod lattice topology obtained by RBTO is more complex than DTO. Furthermore, the plate-rod hybrid lattice topology is obtained when the load density increases under constant total loads. In addition, the uneven distribution of the multi-structural-thermal loads affects the structural and thermal failure positions significantly. More material is located below the higher loads and 3D tree-like topology is generated by RBTO, which is beneficial for force and heat redistributing and transferring uniformly. The above methods and findings have extensive application prospects in topology design of metal foam with efficient heat transfer and load-bearing capacity.

In this paper, the vibration problem of a rectangular plate rested on a viscoelastic substrate and consisting of porous metal foam is solved via an analytical method with respect to the influences of various porosity distributions. Three types of porosity distribution across the thickness are covered, namely uniform, symmetric and asymmetric. The strain–displacement relations of the plate are assumed to be derived on the basis of a refined higher-order shear deformation plate theory. Then, the achieved relations will be incorporated with the Hamilton’s principle in order to reach the Euler–Lagrange equations of the structure. Next, the well-known Galerkin’s method is utilized to calculate the natural frequencies of the system. The influences of both simply supported and clamped boundary conditions are included. In order to show the accuracy of the presented method, the results of present research are compared with those reported by former published papers. The reported results show that an increase in the porosity coefficient can dramatically decrease the frequency of the plate. Also, the stiffness of the system can be lesser decreased, while a symmetrically porous metal foam is used to manufacture the plate.

The use of metal foams for damping vibrations of mechanical structures has found interesting applications in machine tools and its components. Indeed, undesired vibration is one of the most detrimental causes that limit the machine performance in terms of the maximum achievable material removal rate MRR. Although positive results were presented in some research works, a methodology for predicting the damping properties of such materials in the machine tool design phase using finite element codes is still missing. In order to bridge this gap, in this paper, an experimental procedure for identifying the damping contribution of the aluminum metal foam to the hosting structure is proposed. The experimental data are even used to develop a model for predicting the damping. The procedure is further validated on a dummy structure.