A DCAMM seminar will be presented by
Andrew Kraynik
Sandia National Laboratories (retired)
Albuquerque, NM, USA
and
University of Erlangen-Nuremberg, Germany
Abstract:
Foam micromechanics is aimed at predicting macroscopic mechanical behavior by analyzing deformations at the cell level. This talk will focus on the linear elastic response of low-density open-cell foams by examining a wide range of models for ordered and random foam structure. Ordered foams, such as the Kelvin and Weaire-Phelan structures, are natural starting points for modeling open-cell foams but they lack two key features of real materials: random cellular morphology and polydispersity – positional and size disorder, respectively. Finite element analysis is used to calculate the elastic moduli of random open-cell foams for three different models of random foam structure: 1) Voronoi polyhedra based on random packings of monodisperse spheres, 2) Laguerre polyhedra derived from dense packings of polydisperse spheres, and 3) soap froth produced by minimizing surface area with the Surface Evolver. The cell vertices are connected with straight beams of uniform Plateau-border cross section to model the network of struts in open-cell foams. The effect of foam poly-dispersity on the elastic moduli for various models of foam structure will be discussed.
The crushing behavior of open-cell Al-alloy foam is investigated for realistic models of foam structure based on random soap froth. The struts are modeled as shear-deformable beams with variable cross sections to match the shapes found in real foams; they are discretized with beam elements in LS-DYNA, and the Al-alloy is modeled as a finitely deforming elastic-plastic material. The quasi-static crushing response exhibits a relatively stiff linearly elastic regime that terminates into a load maximum, which is followed by an extended plateau during which localized cell-crushing initiates and gradually spreads throughout the specimen. When most of the cells are crushed, the densified material, in which struts contact, stiffens again. Beam contact is an essential feature of the crushing simulation. The models reproduce all aspects of quasi-static crushing.
Danish pastry, coffee and tea will be served 15 minutes before the seminar starts.
All interested persons are invited