Metallic foams are a new category of metals with a porous structure which possess new mechanical, thermal, electrical and acoustic properties including low density with simultaneously high stiffness, and acoustic and thermal insulation. These materials are utilized as a sandwich core to decrease the structure total weight and also, energy absorption and damping. Wide range of metallic foam application makes it necessary to develop a modeling method which can be used in the numerical study of the mechanical behavior of these materials. In this regard, a novel geometrical modeling approach is proposed to produce a geometrical model of the foam. This is based on subtracting spherical pores with a random size and random position from the solid sheet which makes a more realistic way of foam sheet modeling. Most of the prior approaches use a repeating unit cell structure. Thus, three algorithms, including progressive subtraction, incremental and random-based subtraction of the pores are presented and developed. The proposed model validation is carried out based on geometrical aspect and with the comparison of four parameters such as relative density, cell size ranges, distribution of cell sizes in the foam structure and mean cell sizes. Results show a close agreement between modeled foams with real ones. Also, geometrical study results that with an increase in the mean cell size, relative density first increases and then decreases.

Two-layer metallic sheets have wide applications in aerospace, marine, automotive and domestic industries due to their superlative characteristics. In this paper, the formability of two-layer sheet is investigated through analytical, experimental and numerical approaches. An analytical model is developed based on Marciniak-Kuczynski method associated Hill’s non-quadratic yield criterion. Forming limit diagrams are also obtained numerically based on finite element method using Bifurcation theory and ductile fracture criteria. Furthermore, experiments are carried out on Al3105-St14 two-layer sheet. Theoretical results from various methods are compared with results obtained from experiments to evaluate the competency of discussed analytical and numerical methods to predict the formability of two-layer sheets. The results show that analytical and numerical approaches discussed in this paper have good capabilities to predict the formability of two-layer sheets. However, the analytical method based on M-K model and numerical approach based on bifurcation theory are more suitable to determine the forming limit diagram of Al3105-St14 two-layer sheets.

Nowadays, two-layer metallic sheets have become as a useful solution to produce multi-functional products. Generally, two-layer metallic sheets can have advantageous characteristics such as increasing formability of the low formable component, improving the corrosion and wear resistance and reducing weight and cost of manufactured products. Therefore, understanding the forming limit behavior of a two-layer metallic sheet has an essential role in the design of sheet metal forming processes. Forming limit diagram (FLD) is a suitable method to predict the formability of metallic sheets in sheet metal forming operations. The aim of this research was to determine the forming limit diagram in Aluminum-Copper two-layer metallic sheets experimentally. The forming limit diagram can be used as a criterion in order to predict necking initiation which may cause tearing in sheet metal forming processes. In this paper, the forming limit diagrams of Aluminum-Copper two-layer metallic sheets have been obtained through an experimental procedure for the first time.

Protective steel doors are widely used in buildings due to their high resistance against the impact loads. However, its heavy weight has been always considered as a major drawback for these doors. In this paper, a new optimized stiffened impact-protective steel door incorporating sandwich panel with aluminum foam core (OSSA) is examined. This door consists of two face sheets, main and secondary stiffeners, and aluminum foam as the inner core. In order to optimize the door, at first the rigidity and weight functions of the stiffened steel door were extracted. Then an optimal door weighing 42% less than the primary door was obtained. Due to the high energy absorption capacity of the combined foam core and stiffened steel door structure, the use of aluminum foam core in the optimized steel door was proposed. By doing numerical analysis, and depending on the thickness of the face sheet of OSSA, 20 to 32% reduction in the maximum displacement was observed. The results also showed that, with 67% increase in the peak overpressure, OSSA has kept almost the same maximum displacement as that of the steel door without an aluminum foam. In other words, by using aluminum foam core in the optimized stiffened door, the door will resist 67% more impact load.

Nowadays, two-layer sheets have many applications in various industries due to their superlative characteristics. Characteristics such as weight and formability of two-layer sheet depend on the material and the thickness of the layers which compose the two-layer sheet. Plastic instability and occurrence of localized necking limit the forming of the sheets. Forming limit diagram is used to evaluate the formability of sheet. In this paper, a multi-objective genetic algorithm is applied to optimize the thickness ratio of layers in Al3105-St14 two-layer sheet. The optimal model minimizes the weight and maximizes the formability of two-layer sheet simultaneously. Forming limit diagram of two-layer sheet is determined by analytical model based on Marciniak and Kuckzinsky (M-K) method using Barlat and Lian non-quadratic yield criterion. Experiments are also carried out on Al3105-St14 two-layer sheet in order to examine the validity of the theoretical results. Pareto-based multi-objective optimization is used in order to make the objective function of weight per unit area minimized and the objective function of formability maximized. The Pareto front provides a set of optimal solutions. In addition, the knee point as the most satisfactory solution from Pareto-set is determined using minimum distance method.

In a laser forming process, the temperature gradient across the sheet thickness produces the final bending angle. Metallic foams cannot be formed by any mechanical processes due to occurrence of failure during deformation. In this article, closed-cell aluminium foams are irradiated by a laser beam. Experiments are carried out by varying laser power, scan velocity and the number of scan passes to specify their effect on the bending angle. Design of experiment with the response surface methodology and analysis of variance are utilized to analyze parameter effects. At last, an equation is derived for prediction of bending angle.

Sandwich structures are widely used in aerospace, automobile, high speed train and civil applications. Sandwich structures consist of two thin and stiff skins and a thick and light weight core. In this study, the obligatory mandate of a sandwich plate contact constitutes a flexible foam core and composite skins with a hemispherical rigid punch has been studied by an analytical/empirical method. In sandwich structures, calculation of force distribution under the punch nose is complicated, because the core is flexible and the difference between the modulus of elasticity of skin and core is large. In the present study, an exponential correlation between the contact force and indentation is proposed. The coefficient and numerical exponent were calculated using the experimental indentation results. A model based on a highorder sandwich panel theory was used to study the bending behavior of sandwich plate under hemispherical punch load. In the first method, the force distribution under the punch nose was calculated by the proposed method and multiplied to deformation of related point in the loading area to calculate the potential energy of the external loads.In the second method, the punch load was modeled as a point force and multiplied to deformation of maximum indented point. The results obtained from the two methods were compared with the experimental results. Indentation and bending tests were carried out on sandwich plates with glass/epoxy skins and a styrene/acrylonitrile foam core. In the bending test, a simply support condition was set and in the indentation test the sandwich specimens were put on a rigid support. Indeed, in this position the punch movement was equal the indentation. The comparison between the analytical and experimental results showed that the proposed method significantly improved the accuracy of analysis.

In this paper, an analytical solution for the static indentation and low velocity impact response of composite sandwich beams with an orthotropic symmetric composite face-sheets and foam or honeycomb core is presented. The indentation force during impact loading consists of two regimes, one for small indentations of the top face-sheet due to bending moments and the other for larger deformation due to membrane forces. Also, the crushable core is considered a rigid-plastic foundation, and the elastic aspect is neglected. To obtain a more accurate approximation of the static indentation of the beam, both the local and global deformation of the sandwich beam are considered. The minimum potential energy method is applied for the extraction of governing equations. Furthermore, by developing a three dimensional finite element model through the ABAQUS code, the low velocity impact on composite sandwich beams with foam core is simulated. The contact force history, maximum contact force, and upper face-sheet displacement results computed by the analytical model are compared with experimental and ABAQUS simulations. A good agreement between the analytical model, finite element simulation, and experimental results, is observed.