The fan case in a jet engine is required to contain a fan blade in the rare event of a blade loss during operation. Because of its function, the fan case is the largest structural component in high-bypass-ratio turbofan engines used in commercial aircraft. Therefore, the use of lighter and stronger materials would be advantageous in most engines and is practically a necessity in the latest generation of high-bypass engines.
Ballistic limit versus areal weight for Haynes 25 and several other metallic systems at room temperature, showing the advantage achieved by Haynes 25, especially at higher velocities.
Small panels, 7 in. wide by 7 in. long, of a number of metallic alloys were impact tested at room temperature with a 0.50-caliber blunt-nose titanium alloy projectile at the NASA Glenn Research Center (ref. 1). These metallic systems included several high-strength aluminum (Al) alloys, Al-based laminates, aluminum metal matrix composites (Al-MMCs), nickel-base superalloys (Inconel 718 and 625), several titanium (Ti) alloys in different heat-treated conditions, 304L stainless steel, a stainless-steel-based laminate, and a high-strength steel (Nitronic 60). It was determined that a simple Co-base alloy (Haynes 25) had the best impact resistance on an areal weight basis as shown in the preceding graph. Haynes 25 was at least 10 percent better than IMI 550, the best titanium alloy tested to date, and it was far superior to other metals, especially at higher impact velocities (greater than 1100 ft/sec).
Because this material could be ideal for fan containment applications in supersonic aircraft as a replacement for titanium, impact tests were also conducted at 371 oC and compared with results from alloys tested at elevated temperature under previous programs (i.e., Inconel 718, Ti-6242, M-152, Timetal 21S, and Aeromet 100). The following graph clearly indicates that Haynes 25 is approximately 10 percent better than the Ti-6242 and approximately 20 percent better than Inconel 718, evaluated on the basis of velocity versus areal weight.
Ballistic limit versus areal weight for Haynes 25 and several other metallic systems at 371 °C, demonstrating the superior performance of Haynes 25 at elevated temperatures.
Although cobalt-base alloys are used in some high-temperature engine applications, to our knowledge they are not used in any containment systems. Advantages of cobalt over titanium include lower cost, easier processing, better high-temperature strength, and no fire hazard if tip rub occurs. Future plans include testing of lightweight sandwich panels with Haynes 25 as a core material in the form of a foam or lattice block structure and scaling up the current tests by using blade-simulating projectiles impacting large plates and half rings.
Find out more about Glenn's ballistic impact research.
Ohio Aerospace Institute (OAI) contact: Dr. Mohan G. Hebsur, 216-433-3266, Mohan.G.Hebsur@grc.nasa.gov
Glenn contact: Dr. Ronald D. Noebe, 216-433-2093, Ronald.D.Noebe@nasa.gov
Authors: Dr. Mohan G. Hebsur, Dr. Ronald D. Noebe, and Duane M. Revilock
Headquarters program office: OAT
Programs/Projects: Propulsion and Power, Ultra Safe
Last updated: June 25, 2003
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