Cell Wall Fracture in Shock-Loaded Aluminum Foams

A unique phenomenon of cell wall fracture was observed in shock-loaded closed-cell aluminum foams at the loading face. Microstructural analysis revealed that the cell wall fracture occurred over a limited length near the loading face, while foam densification occurred over the remaining length of the foam. The frequency of occurrence of cell wall fracture decreased with increasing foam density. Plate theory was used in combination with experimental cell wall fracture data under point loading to estimate static pressures required for cell wall fracture. In spite of considerable scatter, owing to the stochastic cell geometry, the estimated static fracture pressure increased with foam density, which indirectly corroborates well with the reduced occurrence of cell wall fracture in higher-density foams under constant shock pressures. The value of the experimental shock pressure which caused cell wall fracture, however, was much lower than the predicted static cell wall fracture pressures. This underlines the higher damaging ability of shock loads compared to static loads in causing cell wall fracture in closed-cell aluminum foams, which may affect the structural as well as acoustic properties of the foam.