A new study has demonstrated that Composite Metal Foam (CMF), a novel lightweight material, exhibits an extraordinary ability to resist puncture and impact.
Particularly, this lightweight material is tough enough to block forces that would ordinarily punch a hole clean through a railroad tank car.
The team from North Carolina State University in the US states that this discovery could enhance safety standards governing the transportation of hazardous materials, especially for railroad tank cars.
Hazardous material transportation
CMFs are not new. In the past, experts have created these materials for use in engines and nuclear reactors.
The material is fabricated from a metallic matrix into which hollow spheres (often stainless steel or nickel) are structurally integrated, forming a specialized metallic foam.
As a result of this unique structure, this foam material offers both minimal weight and strength against crushing forces.
Apart from its strength, CMF offers better heat resistance: it is a superior insulator and does not weaken as much as steel when temperatures rise.
The combination of lightweight strength and thermal insulation gives CMF promise for high-stakes applications.
In transportation and defense, the material offers advantages for designing aircraft wings, vehicle armor, and body armor.
Moreover, it is an ideal candidate for safety and storage, specifically in the handling and transport of nuclear material, explosives, and various other hazardous or heat-sensitive substances.
The study focused on CMF’s use in railroad tank cars, which transport hazardous materials like acids, chemicals, petroleum, and liquefied natural gas.
Due to the toxic substance nature, the material used in their manufacture must meet the very rigorous testing requirements set by the U.S. Department of Transportation (DOT).
“In previous studies, CMF has passed these tests with flying colors, and the next step for us was to see how the material performed in puncture tests. The results were outstanding,” said Afsaneh Rabiei, corresponding author and a professor of mechanical and aerospace engineering at North Carolina State University.
Shows promise in testing
Researchers tested puncture resistance using a 300,000-pound ram car on train tracks.
Equipped with a six-inch-square steel indenter, the ram car was accelerated to 5.2 miles per hour on the train tracks.
At this speed, an indenter mounted on the ram car was driven into the type of high-quality steel plating used in railroad tank cars.
The combined speed and weight resulted in a massive impact force of 368 kilojoules concentrated across the face of the indenter.
In the test, the powerful indenter ripped a significant hole straight through a standard high-quality steel tank car plate.
However, when a mere 30.48-millimeter (approximately 1.2 inches) thick layer of CMF was placed on the indenter, the results were dramatically different.
Instead of puncturing the plate, the CMF layer successfully shielded the steel from damage. It absorbed nearly all the impact energy, causing the indenter and ram car to bounce off and inflict only minor damage immediately.
“The obvious conclusion here is that lightweight CMF can absorb puncture and impact energies more efficiently than solid steel,” Rabiei said.
To maximize the material’s potential, researchers have developed a computational model that streamlines the design process. Interestingly, the model can calculate the precise CMF thickness required to provide the desired protection. It suggests that even thinner layers could provide superior protection.
The findings were published in the journal Advanced Engineering Materials.
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