On the quasistatic and dynamic behaviour of foam-filled structures.

摘要

Metallic foams and foam-filled structures have received an increasing attention over the past decade due to their superior specific mechanical properties and low weight. The mechanical behaviour of metallic foams and foam-filled structures has been frequently studied using oversimplifying approaches, which overlook the cellular nature of the material and assume full periodicity of the foam, thus ignoring edge and non-uniform cell-size effects. These approaches also do not take into account the effect of geometric imperfections and material defects on the behaviour of the foam and foam-filled structures.; In this work, we overcome these deficiencies using a multi-cell approach that accurately models the mechanical behaviour of metallic foams and foam-filled structures. Three aspects of the work are accordingly examined. The first is concerned with investigating the effect of critical material and geometric imperfections on the mechanical behaviour of foam. A representative unit-cell model is modified in order to account for different imperfections, which are introduced in accordance with experimentally observed and measured values. The work was carried out using LS-DYNA explicit finite element solver. In the second, attention is devoted to the collapse of square aluminium alloy columns, which are used as the outer shell in foam-filled structures. This part of the work investigates the influence of specific symmetry boundary and initial conditions on the collapse behaviour of the column. The results show that finite element model reduction and symmetry conditions must be used with proper care because of possible numerical anomalies. Furthermore, careful experimental work should be carried out to validate the FE predictions.; In the third, the developed multi-cell approach is employed to study the collapse of foam-filled columns under quasi-static and dynamic loadings. The effect of foam density, column wall thickness, and impact speed on the instantaneous load-deformation and energy absorption characteristics is evaluated and discussed. The results reveal that the existence of the foam as a filler can lead to a marked increase in energy absorption characteristics of foam-filled structures.