Researchers at North Carolina State University, Raleigh, have fabricated strong heat-resistant sheets of aluminum foam by depositing a foaming agent between two thin sheets of aluminum dotted with indentations, then heating until the agents decomposed and formed pores. The foamed aluminum weighs about 20 to 30% less than the bulk material, yet offers a 30 to 50% increase in bending strength. The tensile strength is nearly identical to that of the original sheet metal.
Prof. Afsaneh Rabiei developed the material for protection in areas that are only a few millimeters thick. To be effective, such materials must be thin enough to fit inside tightly spaced product linings, flexible enough to withstand twisting and bending, and strong enough to protect the contents inside.
“This material does exactly what sheet metal and other bubble wraps do, but better,” said Dr. Rabiei, professor of mechanical and aerospace engineering and the lead researcher on the project. “And it won’t cost businesses and consumers very much because producing it requires just a few steps.”
To create the bubble wrap, Rabiei started with a thin sheet of aluminum and used a studded roller to dot the material with small indentations. Then she deposited a foaming agent – such as calcium carbonate or titanium hydrate – into the indentations. When heated, such agents decompose and create bubbles. Prof. Rabiei covered the aluminum with another sheet, sandwiching the foaming agent in its indentation troughs. She ran a heavy roller over the two sheets to bond them together. In the final step, she placed the combined sheet into a furnace, where the heat broke down the foaming agent and created air bubbles in the material. The process is akin to baking soda causing batter to rise when baking a cake.
