Composite 'bird strikes' examined using acoustic microscopy

Composite "bird strikes" examined using acoustic microscopy

Keywords: Composites, Turbines, Scanners, Flight safety, Aircraft

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) material 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 146ms^-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 500úC to restore its internal structure.

It is reported that 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.

Further details are available from Materials World, Institute of Materials. Tel: +44 (0)171 451 7395; Fax: +44 (0)171 839 4534.