Creep of closed-cell aluminum foams: Effects of imperfections and predictive modeling

Abstract

The influence of five different types of morphological imperfection – curved cell wall, corrugation, cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness – on steady state creep of closed-cell aluminum foams is systematically studied under uniaxial compressive loading. A refined theoretical model is developed to predict the steady state creep rate of idealized tetrakaidecahedral (TKD) closed-cell foams. Based upon the TKD model, finite element modeling is also carried out. The presence of imperfections usually leads to significant increase in steady state creep rate. The creep rate increases linearly with the degree of cell shape irregularity and the curvature of curved cell walls, while increases as a power law function of the area fraction of missing cell walls and the dispersion degree of non-uniform distributed cell wall thickness. The combined effect of three different random defects—cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness—causes more drastic increase in creep rate than any single or dual imperfections. Interactions among the three are small and can be neglected. Finally, an empirical formula of steady state creep rate is proposed to give a good prediction for closed-cell foams with random imperfections.