Keywords: aluminium foam, material identification, inverse finite element modeling, isolated cell-wall, three-point bending, scanning electron microscope.

This paper describes the determination of the elasto-plastic properties of base material of aluminium foam Alporas. Three point bending experiments at the micro-scale level in conjunction with inverse finite element simulation were performed. In the cellular structure cell-walls with planar shape were identified and vicinity of such walls was extracted. Harvested material was embedded into transparent rosin to avoid plastic deformation during the manipulation and the selected wall was extracted. The specimens were finalized by grinding and polishing to achieve approximately rectangular shape. Three projections were acquired using a scanning electron microscope (SEM) and a volumetric model of the samples was developed using a semiautomatic image processing tool.

A micro-scale three-point bending test of semi-prismatic specimens extracted from the cell-wall was performed using a custom designed loading device. Loading was provided using a preloaded lead screw with precise travel. Applied force was measured using a high-accuracy load cell with a loading capacity of 2.25N. Strains were measured optically using the digital image correlation method.

The volumetric model developed from the set of SEM projections was discretised using tetrahedral elements with quadratic shape functions. In the simulated bending test the elasto-plastic material model with the von Misses yield criterion and bilinear isotropic hardening was used. Boundary conditions consistent with the experimental ones were prescribed in the simulation. The measured force was sampled at 50Hz and applied to the finite element model. Based on the measured displacements, parameters of the material model were varied to obtain a best fit to the experimental data (load-deflection curve). Elastic and plastic material constants of the constitutive model were identified: (i) Young's modulus of elasticity, (ii) yield stress and (iii) tangent modulus.

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