Date of Award
Master of Science in Mechanical Engineering and Applied Mechanics
Mechanical Engineering and Applied Mechanics
Martin H. Sadd
This study used an open source three-dimensional Voronoi cell software library to create nonlinear finite element models of open cell metal foams in the 5% to 10% relative density range. Cubic and Body-Centered Cubic (BCC) seed point generation techniques were compared. The impact of random positional perturbations on original seed points was investigated as it relates to material stiffness and yield strength. The models simulated a 10-cell cube of foam material under uniaxial loading at strain rates of around 100/s up to about 80% compressive strain. It was shown that the models created with BCC seed points generally had a higher modulus which was less sensitive to perturbations in seed point location. The models were compared to drop-weight experiments on ERG Duocel metal foams of 10, 20, and 40 Pores Per Inch (PPI) which were filmed with a high speed camera. The models showed good agreement with analytical predictions for material properties, but a comparison with experimental data indicated that they lost accuracy in simulating material response after 50% compressive strain. Past this point, cell-wall contact within the foam is a dominant mechanism in the mechanical response, and model predictions did not appear to match well with experimental data.
In a parallel experimental effort ERG foams of 10 PPI and around 8% relative density were subjected to tensile loading at a strain rate of 73/s. High speed photography was again used to interpret the data. The Young's modulus and yield strength of these foams were shown to increase by a factor of ten as compared to quasistatic values, indicating significant rate dependence.
Murphy, Colin J., "Nonlinear Finite Element Modeling of Cellular Materials Under Dynamic Loading and Comparison to Experiments" (2016). Open Access Master's Theses. Paper 806.