Effect of displacement-rate on the indentation behavior of an aluminum foam

Abstract

The deep indentation response of a closed-cell aluminum foam under different rates of penetration, ranging from 1.5 × 10⁻² to 5 × 10³ mm s⁻¹, was experimentally investigated. Two types of indenter geometries were utilized: a flat-ended punch (FEP) and a spherical-ended punch (SEP). Indentation test results obtained are compared with the results under uniaxial compression tests conducted with varying strain rates. Experimental results show that the indentation load-displacement response obtained using the FEP is similar to that observed under uniaxial compression. In all the cases, the plastic strength and the absorbed energy per unit deformed volume of the material increases linearly with increasing logarithm of displacement rate. Cross-sectional views of the indented specimens show that the deformation is confined only to the material directly beneath the indenter with very little lateral spread, a consequence of the near-zero plastic Poisson's ratio of the foam. The computed densification strain in the case of FEP indentation is similar to that observed in uniaxial compression, but significantly lower than that observed in SEP indentation. The shear strength and energy, extracted from the indentation data, agree well with those reported in the literature.