On the layered micromechanical three-dimensional finite element modelling of foam-filled columns

Abstract

In this article, a new micromechanical layered model is proposed for the finite element analysis of the quasi-static collapse of foam-filled ultralight aluminium box sections. The foam was modelled using a novel micromechanical approach in which the localised deformation of the foam was simulated using a discrete number of layers joined together at coincident nodes. The coincident nodes were subject to a tie-break criterion to allow the proper deformation of the foam. The newly proposed layered approach allows for the local penetration of the folds and shearing of the foam, as observed in testing, thus avoiding the commonly adopted approximations in which the foam must undergo global deformation to accommodate the externally applied loads. In this three-dimensional non-linear finite element model, the aluminium box 6061-T4 was assumed to be a Mises-type material that follows the isotropic hardening criterion. A specially developed constitutive law was used for the foam material to account for the hydrostatic component as well as the independence of the strain tensor components. Three types of contact were used in the model. An automatic surface to surface contact algorithm between the foam layers and the column wall. A single surface contact algorithm is used for the column so as to avoid interpenetration of the column walls. A node to surface contact is used between the rigid massless striker and the top of the column. Comparison with the experimental results of a number of foam-filled aluminium 6061-T4 box structures shows excellent agreement with the finite element predictions in terms of the number of folds developed, the instantaneous load–displacement relationship and the average collapse load versus displacement.