"CMF has many attractive properties, which make it appealing for a wide range of applications," says Afsaneh Rabiei, corresponding author of the paper and a professor of mechanical and aerospace engineering at North Carolina State University. "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."
CMF consists of hollow metal spheres made from stainless steel, nickel or other alloys embedded in a metallic matrix, yielding a high strength-to-weight ratio and excellent energy absorption. Prior studies also showed CMF insulates heat better than conventional metals, enabling prospective roles in storing and transporting nuclear and other heat-sensitive or hazardous materials.
To probe fatigue behavior at temperature, the team tested steel-sphere-in-steel-matrix CMF at NC State's Constructed Facilities Laboratory. Samples experienced compression-compression fatigue cycles at 23C, 400C and 600C. At 400C, CMF endured loading between 6 and 60 MPa (about 870 to 8702 psi) for more than 1.3 million cycles before the time-limited test ended without failure.
At 600C, CMF withstood cycling between 4.6 and 46 MPa (about 667 to 6671 psi) for over 1.2 million cycles, again without failure when the test was stopped for time. The researchers note solid stainless steel typically shows sharply reduced fatigue life as temperature rises from room temperature to 400C and 600C, making CMF's stable performance particularly notable.
"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, 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 open-access paper lists first author Zubin Chacko, with co-author Gregory Lucier, both from NC State. Funding came from the US Department of Transportation's Pipeline and Hazardous Materials Safety Administration under project PH95720-0075. A conflict-of-interest note states that Rabiei invented CMF and assigned related intellectual property to a small business in which she is a shareholder.
Research Report:Performance of Composite Metal Foams Under Cyclic Loading at Elevated Temperatures
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