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Composite metal foam: Resilient against high stresses at high temps

By Matt Shipman, North Carolina State University

New research shows that composite metal foam (CMF) is incredibly resilient at high temperatures, able to withstand repeated heavy loads even at temperatures of 400 and 600 degrees Celsius. Coupled with the material's high strength-to-weight ratio, the finding suggests CMF could be used in applications ranging from automobile engines to aerospace components to nuclear power technologies.

CMFs are foams that consist of hollow spheres -- made of materials such as stainless steel, nickel, or other metals and alloys -- embedded in a metallic matrix. [Credit: Photo courtesy of NC State]

 

 

 

 

"CMF has many attractive properties, which make it appealing for a wide range of applications," says Afsaneh Rabiei, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University (NC State). "But if you want to use a material in engines, airplane parts, or any application involving repeated loading and high temperatures, you need to know how the material will perform.

"This is important for any application, but particularly when equipment failure could affect public health and safety such as jet engine vanes, ducts, and exhaust flaps; turbine blades; hypersonic vehicle airframes and hot trailing edges of wings; gas and steam turbines; automobile brake system components and internal combustion engine parts; nuclear reactor fuel cladding; and many more structures that go in service under extreme conditions of heat and load."

CMFs are foams that consist of hollow spheres -- made of materials such as stainless steel, nickel, or other metals and alloys -- embedded in a metallic matrix. The resulting material is both lightweight and remarkably strong at absorbing compressive forces, with potential applications ranging from aircraft wings to vehicle armor and body armor.

In addition, CMF is better at insulating against high heat than conventional metals and alloys, such as steel. The combination of light weight, strength, and thermal insulation means that CMF also holds promise for use in storing and transporting nuclear material, hazardous materials, explosives, and other heat-sensitive materials.

To see how CMF would perform under repeated stress at high temperatures, the researchers worked with NC State's Constructed Facilities Laboratory, which is designed to test materials and structures under extreme circumstances.

For this study, the researchers worked with CMFs consisting of steel spheres in a steel matrix. The CMF samples were put through a repeated cycle of loading while exposed to temperatures of 23 C (73 F), 400 C (752 F), and 600 C (1,112 F).

At 400 C, the CMF withstood a cycle of loading that alternated between 6 and 60 megapascals (or between 870 and 8,702 units of pound-force per square inch) for more than 1.3 million cycles without failure before the researchers halted the test due to time constraints.

At 600 C, the CMF withstood a cycle of loading that alternated between 4.6 and 46 megapascals (or between 667 and 6,671 units of pound-force per square inch) for more than 1.2 million cycles without failure before the researchers halted the test due to time constraints.

"Knowing that in a compression-compression fatigue setting, the fatigue life of solid stainless steel decreases significantly as temperature increases from room temperature to 400 C and 600 C, these results were remarkable," Rabiei says. "Our findings indicate the fatigue life of the steel-steel CMF is not diminished and that this lightweight material performs tremendously well in the extreme environment of high-temperature cyclic loading.

"This discovery is exciting, and we're open to working with industry partners who would like to explore potential applications for CMF. This work was done with an eye toward developing a material that could be used to improve safety and efficiency related to the shipping of hazardous materials (see SIDEBAR), so that's one potential application. But these findings are also relevant to any application where equipment may be exposed to high loads and high temperatures."

The paper, "Performance of Composite Metal Foams Under Cyclic Loading at Elevated Temperatures," is published open access in the Journal of Materials Science.

SIDEBAR: CMF -- A sort of "force multiplier" for materials
By Tracey Peake , North Carolina State University

A new study by researchers at NC State also found that composite metal foam (CMF) can withstand tremendous force -- enough to punch a hole in a railroad tank car -- at much lower weight than solid steel. The finding raises the possibility of creating a safer generation of tanker cars for transporting hazardous materials.

Left to right: CMF installed on top of the indenter, sensor attached to CMF, and CMF after puncture test. [Credit: Photo courtesy of NC State]

 

 

The researchers have developed a computational model that can be used to determine what thickness of CMF is needed in order to provide the desired level of protection necessary for any given application.

"Railroad tank cars are responsible for transporting a wide range of hazardous materials, from acids and chemicals to petroleum and liquefied natural gas," says Afsaneh Rabiei, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at NC State. "The safety of these tank cars is important, and the U.S. Department of Transportation has very rigorous testing requirements for any material that might be used to manufacture these tank cars.

"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 testing," Rabiei says. "The results were outstanding."

For the puncture testing, the researchers used a 300,000-lb ram car that runs on train tracks. The ram car was mounted with an indenter -- essentially a steel column with a point that measures 6 in.². The ram car was accelerated to 5.2 mph, at which point the indenter would collide with the type of high-quality steel plating used in tank cars. The speed and weight of the ram car generated 368 kilojoules of force, distributed across the 6-in. by 6-in. end of the indenter.

In the baseline test, the indenter tore a gaping hole in the steel plate. For the experimental test, the researchers placed a piece of CMF that was 30.48 mm thick on the end of the indenter. Upon colliding with a steel plate, the CMF absorbed the vast majority of the force, causing the indenter and ram car to bounce off the steel plate, leaving only a small dent.

VIDEO: A new study finds that composite metal foam (CMF) can withstand tremendous force -- enough to punch a hole in a railroad tank car -- at much lower weight than solid steel. [Credit: Afsaneh Rabiei/NC State]

"The obvious conclusion here is that lightweight CMF can absorb puncture and impact energies more efficiently than solid steel," Rabiei says. "We have a model that can be used to figure how much CMF is necessary, which maximizes the efficiency of using CMF, as we believe that a lower thickness CMF could have performed even better."

The paper, "Numerical Model and Experimental Validation of Composite Metal Foam in Protecting Carbon Steel Against Puncture," is published in Advanced Engineering Materials.

Published November 2025

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