Aluminum Foams Processed by Rapid Prototyping for Lightweight Structures

The demand for faster and lighter land transportation for the troops has increased the need for more efficient structures. Sandwich panels form one type of efficient structure enabling the application of steel, aluminium or composites in the construction. Cellular metals for sandwich structures have been available for decades (Ashby 1998, Fleck 1998, and Gibson 1997), but new opportunities are emerging for two reasons. Novel manufacturing approaches have beneficially affected performance and cost (Akiyama 1987, Baumeister 1991, Jin 1990, Martin 1991, Kearns 1988, Nagel 1998), and higher levels of basic understanding about mechanical, thermal and acoustic properties have been developed (Gibson 1997, Ashby 1998). The high stiffness and yield strength achievable at low density relative to competing materials and systems creates an opportunity for ultralight structure (Ashby 1997), especially for the Future Combat Systems, with integrally bonded dense face sheets. Large compressive strains achievable at nominally constant stress impart a high-energy absorption capacity at force levels of practical relevance for crash and blast amelioration systems (Fleck 1998). Additionally, these materials may be used effectively for either cooling or heat exchange (Evans 1998). An extrusion based freeform fabrication technique (Vaidyanathan, 2000) was employed to fabricate metallic foams. The advantage of controlled pore orientation, size and ability to fabricate directly from a CAD design is that the mechanical properties could be tailored. The compressive deformation behavior of this new type of aluminum foam was assessed under static and dynamic loading conditions. Metal foam parts were fabricated by the sequential deposition of multiple discrete raw material layers. The processing methodology as well as some of the properties is presented here.