A new scanning device developed by researchers at Pennsylvania State University is helping aerospace engineers monitor the potential effects of "bird strikes" on the new composite materials being developed for use as turbine blades in aircraft engines. The technique will enable greater use of composite materials in aircraft engines by allowing researchers to examine the internal characteristics of composite engine parts as they are mended (healed) in-situ.
Materials such as graphite fibre and polyether etherketone (PEEK) matrix laminated composites have been developed through an international effort to produce lightweight and strong materials to replace the heavier super alloys currently used in aircraft engines in order to reduce overall weight and maximise load-bearing capacity. Recent failures in test turbine blades caused by "bird strikes" have shown that maintaining the integrity of blades made from composites is essential. Researchers have also found that quite often surface integrity can belie internal damage.
The new device incorporates a scanning acoustic microscope, allowing researchers to examine the internal structure of the material to see whether any delaminations (separations) have occurred between the graphite fibre and the polymer matrix. Initial experiments have involved using a specimen of composite material damaged by an artificial "bird strike" - a 3 gramme ball of gelatin fired at a piece of graphite fibre-PEEK composite through a gas gun at 146 ms-1.
The specimen was mounted in the chamber of the microscope with the acoustic lens protected from a heating plate by a double-walled cover. Researchers could then observe the material throughout the healing process as it was heated to 500ºC to restore its internal structure.
The new device can be used to test the internal structure of other materials and can also be used by microelectronics companies to look for defects below the surface of computer chips or to study structural detail in integrated circuits.
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Notes For Editors
1. This item is due to appear as "Acoustic microscopy can take the heat" by Chiaki Miyasaka and Bernhard Tittman, in the June issue of Materials World, Volume 7, Issue 6, p.343
2. Materials World is the journal of The Institute of Materials, the professional organisation of materials scientists and engineers working throughout the world in areas involving the use and application of plastics, rubber, steel, metals and ceramics.
3. Brief contents of Materials World are also available on the web: www.materials.org.uk
4. The views and opinions expressed in this article are the views of the author and are not necessarily the views of Materials World, IoM Communications or any other organisation with which they are associated.
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