Different from conventional metal foams, sintered metallic hollow sphere (MHS) material contains a certain volume fraction of enclosed pore space inside the spheres, as well as the interstitial porosity between the sintered neighbors, and this mixed open/closed-cell characteristic offers low density, high stiffness, and good energy absorption capacity. It is a new type of prospective light weight material for automotive and aerospace industry. In this study, the mechanical properties, especially the dynamic behaviors of the MHS materials are examined experimentally. Basic geometrical measurements reveal that the two types of MHS specimens we used were composed of randomly packed hollow spheres with uniform outer radius (0.9 and 1.5 mm) and wall thickness 0.05 mm (relative density < 6%). A very long, plateau length (up to 67% nominal strain) with almost constant stress was found in quasi-static tests, indicating that they are appropriate for energy absorption applications. Dynamic tests were performed by using a modified split Hopkinson pressure bar (SHPB), and significant dynamic strength enhancements were observed. Moreover, based on the experimental observations the relevant collapse and dynamic enhancement mechanisms are discussed, whereas the localization phenomena in dynamic crushing process were revealed by using the particle image velocimetry correlation method.
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