Fracture behavior of low-density replicated aluminum alloy foams

Tensile tests have been performed on replicated aluminum alloy foams of relative density between 4.5% and 8%. During the test the electrical resistance was measured with a four-point set-up and the displacements along the gage section were measured using a digital image correlation (DIC) technique. Right from the start of the tensile test, the strain as observed at the surface with DIC is not uniformly distributed over the sample, but concentrates in bands; this is attributed to density variations. The peak strain, i.e. the strain at the ultimate tensile strength (UTS), increases with decreasing density for densities below 5.5%. For densities above 5.5% fracture occurs in the band with the highest strain, yielding a roughly constant peak strain (near 1.5%). Resistivity data indicate an increased contribution of strut bending compared to stretching for densities below 5.5%, causing a decreased rate of damage accumulation and an increase in the tolerance to damage. Incremental strain maps show that the increased damage tolerance in the low-density samples allows initially formed deformation bands to harden resulting in multiple bands to be involved in the fracture process.