consistently. Te arrangement of cores in the molds is adjusted to achieve variable density steel plates with one side being solid and backed with porous steel foam.
Researching the Feasibility
Materials research is focused on fundamental research to achieve lasting strategic land power domi- nance through structural materials, ballistic materials, and manufactur- ing science, processing and sustain- ment. Structural materials focus on ballistic materials to enhance the performance and efficiency of army weapons and protection systems including lightweight, extreme performance materials, and energy absorbing materials. Manufacturing science, processing and sustainment is focused on dis- covery, innovation, and maturation of manufacturing innovations and understanding material properties and degradation mechanisms to improve durability of army systems in extreme environments. Porous metals made of alumi- num and titanium are becoming increasingly popular as stiff but lightweight materials for use in structural components of auto- mobiles and aircraft. However, engineering applications require stronger and more economical materials than an aluminum or titanium foam can provide. Tradi-
This steel piston was machined from the steel foam billet.
tional structural steel has proven valuable as an engineering mate- rial, but the properties of struc- tural steel have remained invariant for the past century. Research conducted over approxi-
mately the last 10-15 years has shown that it is possible to fabricate steel foams at the laboratory scale and these foams can be made to have potentially desirable mechanical properties. Despite these substantial advances in the materials science of steel foams, a commercially avail- able product remains elusive, and
POTENTIAL STRUCTURAL APPLICATIONS
Steel foam material has many potential applications. For military vehicle components, it could be used for energy absorbing bumpers, door side impact bars, front crash rails, flywheel containment rings, or blast containment components in military trucks and personnel car- riers. Railcar applications could include crash protection components and structural panels. Lightweight pallets and cargo containers, aircraft landing decks elevator decks, deck rams and hatch covers, fire doors, partitions and floors, docks, and cargo loading decks all could be naval applications. Other applications could include steel foam bars and rods, parking floor slabs, factory enclosures, light walls and impact absorption for guard rails, auditorium walls and ceilings for sound absorption, blast protection for vehicles and buildings, and impact absorption for cars.
therefore structural designers have not begun to explore the potential benefits of using steel foam in civil structural applications Perhaps because of the lack of
commercial availability of steel foam, no applications have been devel- oped or widely implemented. In the past few years, interest in metal foams, especially in steel foams, has increased remarkably. Te reason for this is the wide range of applicabil- ity such as lightweight panels, crash energy absorption, exhaust mufflers, vibration and noise control in the automotive industry, filters, heat exchangers, high strength wall panels for sound insulation and bio-medical implants. Steel foams exhibit excel- lent stiffness-to-weight ratios when loaded in flexure. In particular, steel foam panels have higher bending stiffness than solid steel sheets of the same weight.
Te basic objective of the devel-
opment process of metallic foams is the combination of physical and mechanical properties expected from metallic foams such as high stiff- ness, low specific weight, high gas permeability, low thermal conductiv- ity, unusual acoustic properties, high impact absorption capacity and good electrical insulating properties.
36 | MODERN CASTING January 2017
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