It has been proposed in the literature, based on theoretical considerations and on finite-element calculations, that all three stress ten-sor invariants govern the yield surface of cellular materials. Recent experiments on 75 μm pore size aluminium replicated foams (CombazE, Bacciarini C, Charvet R, Dufour W, Mortensen A. Multiaxial yield behaviour of A1 replicated foam, submitted for publication)showed such a dependence of the yield surface in axisymmetric tests. This study explores the yield behaviour of 400 μm pore size alu-minium replicated foams: experiments confirm the influence of the third invariant on the yield surface shape, together with the obser-vations that (i) the yield surface shape does not depend on relative density and (ii) measured flow vectors conform with normality. Asimple parabolic model fitting data in the previous study also captures well the present data Under all tested stress states (biaxial, axi-symmetric and Π-planes in stress space). Biaxial and axisymmetric tests are also performed on 400 μm pore size polyurethane (PU) rep-licated foams with a similar mesostructure. Results show yield to occur at a value lower than predicted by micromechanical models forboth matrix materials (aluminium and PU). This suggests that the "knock-down" factor usually observed between predicted andobserved stress values probably cannot be explained by a lowered yield stress in the material making the foam. The data also suggestan influence of the matrix nature on the yield surface geometry.
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