Flow stress of open-celled aluminum foams based on current density and the optimal foam for energy absorption

Abstract

Aiming to reveal a fundamental property of open-celled foams under large plastic deformation, the present study proposes and examines a hypothesis, that is, a piece of open-celled foam after being compressed to a certain strain without wall fracture can be regarded as a fresh piece of foam characterized by its current density. As an immediate deduction of this hypothesis, the mechanical property of open-celled foam is completely determined by its current density regardless its initial density. The proposed hypothesis is successfully verified by our experimental data. It is shown that the plastic flow stress (expressed in true stress) of a piece of open-celled foam is independent of its initial density and can be predicted by a power function of its current relative density. Based on the power function, the specific energy absorbed by the aluminum foam can be predicted merely from the initial and the final densities of the foam, instead of integrating the measured stress-strain curve, which greatly simplifies the material design for engineering applications. Then an optimization method is proposed to determine the foam with the optimal initial density for absorbing a specified energy. The optimal foam will produce the minimal stress during the energy absorption compared to those with other magnitudes of density. All the analytical predictions are verified by the experimental results.