Experimental investigation on the dynamic behaviour of metal foam: From yield to densification

Large size specimen should be adopted in testing the cellular material with large cell dimension, whereas, experimental investigation on the dynamic densification of large size cellular materials is still a big challenge. In this paper, a new experimental frame has been presented, which could carry out dynamic tests of low strength cellular materials from yield to densification (80% strain). Functionally, this method could be named as a 'direct impact Hopkinson bar test' where the measurement of stress is realized by a two points strain gage measurements technique and the strain is measured by high speed camera and digital image edge detection. The principle to maintain a relative constant impact speed has been discussed as well. With this method, dynamic experiments on a closed-cell metal foam have been carried out, the stress-strain curves from elastic zone to densification zone have been obtained. Results revealed that strain hardening behavior was observed in higher density foam while the lower one exhibited an ideal response of cellular foam: a long plateau before densification. It is also found that the higher density foam has stronger strain hardening.