The scaling of compression strength with porosity for aluminium foams was investigated. The Al 99.96, AlMg1Si0.6 and AlSi11Mg0.6 foams of various porosity, sample size with and without surface skin were tested in compression. It was observed that the compression strength of aluminium foams scales near the percolation threshold with Tf ≈ 1.9 -2.0 almost independently on the matrix alloy, sample size and presence of surface skin. The difference of the obtained values of Tf to the theoretical estimate of Tf = 2.64 ± 0.3 by Arbabi and Sahimi and to Ashby estimate of 1.5 was explained using an analogy with the Daoud and Coniglio approach to the scaling of the free energy of sol-gel transition. It leads to the finding that, there are two different universality classes for the critical exponent T f : when the stretching forces dominate T f = f = 2.1, respectively when bending forces prevail T f = .d = 2.64 seems to be valid. Another possibility is the validity of relation T f ≤ f which varies only according to the universality class of modulus of elasticity in foam.
The foamed panels and sandwiches were prepared by powder metallurgical route using various matrix alloys. The effect of the apparent density, geometry and structure of the foam on its bending stiffhess was studied with respect to the results of the four-point-bending. It has been shown that the modulus of elasticity of the foam cannot be related only to its apparent density, because the distribution of the cell-wall material along the thickness of the foamed panel is not uniform. Therefore the real moment of inertia of the foam's cross-section should be used for the calculation of bending stiffness. This moment can be determined from the square weight of the foamed sample.
Closed-cell aluminium foams (nominal composition: AlSi12Mg0.6Fe0.3) were prepared by the powder metallurgical route (using 0.4 wt.% TiH2 untreated powder as the foaming agent). Pure foams and foams with the addition of 3 vol.% graphite or SiC powder were prepared. The microstructure and mechanical properties of the prepared aluminium foams containing reinforcing particles were investigated at constant density and compared to those of the pure foam. Vibration measurements were performed to determine the damping properties and modulus of elasticity of the foams. Uniaxial compression tests were performed to determine the following mechanical properties: collapse stress, efficiency of energy absorption, plateau length and densification strain of the foams. All the foams behaved in a brittle manner during compression. Finally, the effect of admixed graphite and SiC powders on the properties of the investigated foam was evaluated, discussed and modelled. The addition of powders changed all investigated properties of the foams. Only the efficiency of energy absorption at constant density was almost identical.
Abstract. The zinc foams were prepared by powder compaction method with various types (TiH 2 or MgH 2 ) and various amount (0.3, 0.6 and 1 wt.%) of foaming agent to investigate the effect of colouring of zinc foams during foaming process. It was observed that due to Archimedes' principle foaming agent particles with lower density as liquid zinc float over a liquid. As a result, on the foam outer skin they react with oxygen during cooling of the foam. Therefore, the significant colouring (purple, blue and dark blue) of pure zinc foams prepared using TiH 2 foaming agent was observed. On the contrary, MgH 2 decomposes almost completely during the foaming process of zinc. As a result Mg is either dissolved in zinc foam (Mg 2 Zn 11 ) or MgO of white colour is created. Therefore no significant colouring of pure zinc foams was observed in this case.
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