Papers by Keyword: Cellular Materials

Abstract: This work presents the design of a parametric Kelvin structure in which the relative density of the geometry can be varied by adjusting three parameters: cell diameter, cell wall thickness and cell chamfer radius, the structure consistsing of a tessellation of hollow truncated octahedral. The developed model was evaluated in terms of compressive stiffness for the case of a rigid polyurethane foam of 0.256 relative density. Three models were analyzed in order to determine the influence of geometric characteristics on mechanical properties: a model that presented no chamfer a model that presented a medium-sized chamfer and a model that presented a large chamfer. A mesh convergence study was performed which analyzed the results in terms of accuracy and time expenses for three element sizes for both linear and quadratic elements. Due to the orthotropic nature of the model, its response on both possible loading directions was investigated. Simulation results were compared with experimental results and yielded accurate results for one loading direction, when using the material properties for solid polyurethane described in literature.

Abstract: Cellular Ti-6Al-4V materials with open-cell pore array structures have been fabricated by Electron Beam Melting (EBM) using an Arcam A2X system. The test samples were cylinders 20 mm diam. x 40 mm high, with pore diameters of 1.75 - 2.5 mm and porosities in the range of 61 - 83%. The structures were based on a simple cubic pore array.Sample stiffness and strength were both found to decrease with increasing porosity, exhibiting mean Young’s moduli of 3.5 – 15.6 GPa and mean yield stresses of 20.2 – 93.6 MPa. Finite element analysis (FEA) using ANSYS was performed to model the stress-strain curves for a representative volume, using measured bulk material properties. Stiffness and strength were significantly overestimated by this method, but better agreement with measured data was obtained when the representative volume was extended along the compression axis.

Abstract: A 3D cell-based finite element model is employed to investigate the dynamic biaxial behavior of cellular materials under combined shear-compression. The biaxial behavior is characterized by the normal stress and shear stress, which could be determined directly from the finite element results. A crush plateau stress is introduced to illustrate the critical crush stress, and the result shows that the normal plateau stress declines with the increase of the shear plateau stress, which climbs with the increase of loading angle. An elliptical criterion of normal plateau stress vs. shear plateau stress is obtained by the nonlinear regression method.

Abstract: The research in material science had led to the discovery of new materials; but the real challenge lies in finding suitable application for those materials to be used in various engineering fields. Finding application for a new material is very difficult. Cellular materials have the most promising applications and proved to be satisfactory for its applicability due to their high stiffness-to-weight ratio, better crash energy absorption, fire resistance, non-toxicity, low thermal conductivity, magnetic permeability and lower density. Along with drastic weight reduction and material savings in the case of cellular structures, there are other application-specific benefits like noise and energy absorption, mechanical damping and filtration effects. Various materials exist where weight reduction is the only parameter to be considered but if low weight combined with good energy absorption characteristics or heat resistance is required, then metal foams could be preferred. Possible applications are seen in areas like light weight construction, crash energy absorption, noise control, transport industry, building industry, heat exchangers, purifiers, decoration and arts, etc,. The use of foams can satisfy the demand for light-weighing parts of several branches of industry.

Abstract: Composite materials are the most advanced class of materials invented and produced by humans in modern times as well as a challenge for the future in the field of scientific and technological performance. They are made up of at least two phases of different nature which are so combined to form a new material with a superior combination of properties. They are generally materials with unusual performances on the relationship between properties and specific gravity. Composites are multiphase materials with distinct and well-defined interface between the constituent phases ensuring a transfer of property but can lead to obtaining a product with exceptional performance from the starting material. In this paper we have focused research on Al-Mg alloys with magnesium and silicon carbide (SiC). Stabilized Aluminium Foams (SAF) are new class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. They offer potential for lightweight structures, for energy absorption, and for thermal management; and some of them, at least, are cheap. Metal foams offer significant performance gains in light, stiff structures, for the efficient absorption of energy, for thermal management and perhaps for acoustic control and other, more specialized, applications. They are recyclable and nontoxic. They hold particular promise for market penetration in applications in which several of these features are exploited simultaneously. The paper presents some results related to the research of metallic foams based on AlMg10 metallic alloy obtained by melt bubbled C₄H₁₀ addition of SiC particles. Microsrtucture of these foams is analyzed by using (SEM) Scanning Electron Microscope, laying out the network of pores imbued into each others developed around SiC particles and other issues microstructural characteristics.

Abstract: To obtain SAF we have focused research on Al-Mg alloys with different concentrations of magnesium and silicon carbide (SiC). To obtain these materials has been chosen different gas blowing method (N₂, SO₂ and C₄H₁₀). It was observed that the best results in terms of pore volume gave blowing with C₄H₁₀. The samples obtained were analyzed by optical and electron microscopy.

Abstract: Microtruss cellular metals are a class of multifunctional materials, composed of a regular arrangement of supporting struts. They can be fabricated by stretching perforated metal sheets out of plane by applying force at strut intersections. Once fabricated, external loads are resolved axially along the struts resulting in stretch dominated deformation, yielding enhanced weight specific strength and stiffness at lower densities compared to conventional metallic foams. Given the slenderness of the struts making up the microtruss architecture, failure often occurs by inelastic buckling and is therefore dependent on the rigidity of the strut end constraints. During column buckling the limiting conditions are pin jointed (k=1) and rigid jointed (k=2), with microtruss struts typically having end constraints intermediate to these boundaries. Experimental and finite element methods were used to determine the value of k in IN600 microtrusses. Because of the non-linear stress-strain behavior of the parent metal, the relative significance of end constraint uncertainty is a function of the strut slenderness ratios and the material in question.

Abstract: Based on the principle of pore formation, geometrical model to describe open-cell cellular materials was constructed. The model is rhombus dodecahedron cell shapes with circle-strut and transitional-junction. The dependence of relative density on the microstructure of the model was analyzed; by finite elements method, the relative elastic modulus of the model was calculated, the influence of microstructure and relative density on the elastic modulus was also obtained. The results show that circle-strut radius and transitional-junction curvature radius are the primary factors on relative density increment; nonlinearity of relative density on relative elastic modulus is similar to that of circle-strut radius on relative elastic modulus, is obviously greater than that of transitional-junction curvature radius on relative elastic modulus.

Abstract: The strength enhancement of cellular materials under dynamic compression was experimentally studied in the present paper. A phenomenological model was employed to investigate the entrapped air contribution by introducing a parameter, namely the leaking rate of air. The strength enhancement caused by the entrapped air was then studied for both aluminum honeycombs and foams. It has been found that the pressure change in the entrapped air during dynamic compression is a direct source of strain hardening for aluminum honeycombs whereas it has smaller influence on the strain hardening of aluminum foams. Other sources that might contribute to the strain hardening of cellular materials are also discussed.

Abstract: Foams and other highly porous metallic materials with cellular structures are known to have many interesting combinations of physical and mechanical properties. That makes these systems very attractive for both structural and functional applications. Cellular metals can be produced by several methods including liquid infiltration of leachable space holders. In this contribution, results on metal foams of Cu based shape memory alloys (SMAs) processed by molten metal infiltration of SiO2 particles are presented. By using this route, highly homogeneous CuZnAl SMA foams with a spherical open-cell morphologies have been manufactured and tested. Morphological, thermo-mechanical and cycling results are reported.