A research group at Japan’s National Institute for Materials Science (NIMS) has found out a reliable way to test the integrity of metal blades in jet engines.

The metal blades on turbines found inside these machines are subject to ‘resonance’, or repetitive vibrations. A familiar example of resonance is a playground swing, which acts as a pendulum. Attempts to push the swing at a faster or slower tempo than its resonant or ‘natural’ frequency will result in different shaped arcs. Similarly the blades in turbines also cause resonance, in this case high speed vibration at several thousand hertz (vibrations per second).

Because of this they must be tested for fatigue periodically. Researchers at NIMS have developed fatigue test devices capable of testing at a high frequency (20,000 Hz) using ultrasonic vibration – a vast improvement on existing technology.

turbine jet engine

In a typical gas turbine jet engine, air is compressed by the fan blades as it enters the engine, and it is mixed and burned with fuel in the combustion section. The hot exhaust gases provide forward thrust and turn the turbines which drive the compressor fan blades. © Jeff Dahl

To achieve this, they had to overcome several difficulties. Because ultrasonic fatigue testing uses the phenomenon of resonance, the number of factors influenced by temperature is extremely large, making itdifficult to design a device that takes them all into account. The team also uncovered factors which had been overlooked in conventional research by conducting trial-and-error experiments and succeeded in correcting previous problems. The result was a completely new commercial testing device incorporating a large number of special improvements. The device can perform accurate fatigue tests at temperatures of 1000°C, and is therefore capable of testing metal fatigue under conditions similar to those inside jet engines.

The technology will improve the safety of jet engines and gas turbines, and is also expected to accelerate research and development of materials for use in high strength turbine blades.

For further information contact:

Dr Yoshiyuki Furuya
Materials Reliability Unit
National Institute for Materials Science, Japan
Email: Furuya.Yoshiyuki@nims.go.jp