Acoustic Microscopy Examines Damage To Composite Materials

A new scanning device developed by Chiaki Miyasaka, Bernhard Tittman, and their research team at Pennsylvania State University (State College, PA) is helping aerospace engineers monitor the potential effects of bird strikes on new composite materials being developed for aircraft engine turbine blades. 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 in situ.

Materials such as graphite fiber and polyether etherketone (PEEK) matrix laminated composites have been developed through an international effort to produce lighter weight and stronger materials to replace the heavier super alloys currently used in aircraft engines. These materials will help to reduce the overall weight and maximize the load-bearing capacity of aircraft. Recent failures in test turbine blades caused by "bird strikes" have shown that it is essential to maintain the integrity of blades made from composites. Researchers have also found that internal damage can exist despite surface integrity.

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 fiber and the polymer matrix. Initial experiments have used a specimen of composite material damaged by an artificial "bird strike." This damage was reproduced by firing a 3-g ball of gelatin at a piece of graphite fiber-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 500°C to restore its internal structure.

The new acoustic microscope 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.

This item was originally reported in the June issue of Materials World, the journal of the Institute of Materials. The Institute of Materials is a professional organization of materials scientists and engineers who work throughout the world in areas involving the use and application of plastics, rubber, steel, metals, and ceramics.

For more information, call Andrew McLaughlin at the Institute of Materials at (+) 44-171-451-7395.