Measurement of strain rate sensitivity of aluminium foams for energy dissipation

In this paper the structural performance of aluminium alloy foams have been investigated under both static and dynamic compression loads. Three foam typologies (M-PORE, CYMAT, SCHUNK) in a wide range of density (from 0.14 to 0.75 g/cm3), made by means of different process-routes (melt gas injection, powder metallurgy, investment casting) have been analysed. Foams microstructural characterization has been carried out through morphometric measurements by means of Scanning Electron Microscopy (SEM) and Computed Tomography (CT) and subsequent digital image processing in order to determine average cells size and cell distributions on different section planes. The experimental study aims to assess the strain rate sensitivity and energy absorption capability of commercially available metal foams and to point out the correlation between the mechanical behaviour and the physical and geometrical properties of the foam. It has been found that the specific energy dissipation of foams with similar density can be quite different: for the same volume of foam, average values of 1770, 1780 and 5590 J/kg at 50% nominal compression have been measured on M-PORE (0.19 g/cm3), CYMAT (0.28 g/cm3) and SCHUNK (0.28 g/cm3) foams, respectively. Impact tests showed that the dependence of the plateau stress on strain rate could be considered negligible for M-PORE and CYMAT foams while it is quite remarkable for SCHUNK foams. Moreover, it was found that the peak stress of CYMAT foams has a quite large sensitivity on the loading rate.