The influence of strain-induced damage on the mechanical response of open-cell aluminum foam

Compression and tensile tests have been performed on annealed (AN) and heat-treated (HT) Duocel open-cell aluminum foam (20 PPI) samples for relative densities ranging between 3 and 13%. The novel approach in this work is to study the evolution of damage and to distinguish the influence of ductile and brittle fracture by measuring simultaneously acoustic emission and electrical resistance during tensile tests. The results clearly show that damage accumulation starts before the peak strain and that it becomes a critical factor for the overall ductility. The onset and rate of damage accumulation is affected by the hardening behavior and the failure strain of the struts, both of which depend on the heat treatment and the density. Brittle fracture, which is more commonly found in HT than in AN samples, decreases the failure strain of the struts, thereby affecting the onset and rate of damage accumulation for HT samples. Due to reorientation of the struts and ongoing strain-hardening of the base material the stress increases linearly with increasing strain in the plastic regime. Consequently, a higher peak strain also leads to a higher peak stress.