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Flight Safety

By Rick Robinson


RICHARD NEU PROBES GAS TURBINE RELIABILITY

Richard W. Neu investigates fatigue and fracture in gas turbine engines used in a variety of applications, including powering aircraft. With funding from multinational corporations and the U.S. Department of Energy, he researches degradation issues in metallic alloy systems, focusing particularly on how highly stressed metal parts change over time at the micron scale. 1

The goal of the research is to support the development of gas turbine engine designs with increased integrity, efficiency, and longevity.

Neu, a professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering, studies both jet turbine engines and gas turbines used for land-based power generation. These engines must use special alloy parts and active cooling strategies to survive temperatures that can exceed 1,400 degrees Celsius — hotter than the melting point of most metals.

In such demanding environments, high temperatures and mechanical stress take a toll. In one investigation, Neu and his team compared the microstructure of an engine turbine blade in service for three years to an unused blade. 2 Structurally, the two blades turned out to be “vastly different,” reported Neu, who directs the Mechanical Properties Research Laboratory at Georgia Tech.

And there’s an added durability challenge – both fatigue cracking behavior and the degradation of the microstructure depend on exactly how and when engine parts encountered temperature and stress during usage periods. Neu simulates these complex thermo-mechanical cycles in the laboratory to characterize material degradation under real-world operating conditions. 3

Neu typically tests nickel base superalloys, which are widely used in gas turbine engines, but he’s also studying promising newer materials. These include molybdenum-silicon-boron refractory alloys, which resist ultra-high temperatures and could replace superalloys in components that must withstand the most aggressive environments; and gamma titanium aluminides, novel temperature-resistant metals that are lightweight enough to be potentially revolutionary for aerospace applications.

This image shows a thermo-mechanical fatigue crack in a nickel base superalloy. Oxidation of the crack is evident.

An airfoil removed from an industrial gas turbine after 32,000 hours of service shows the harsh conditions the blades must withstand.

In this thermo-mechanical fatigue experiment, the temperature of a nickel base superalloy specimen was cycled between thermal extremes.

(Images 1, 2 and 3: Richard Neu, turbine Illustration: Getty Images)

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