A new technique for improving the mechanical properties of the metals and alloys used in the aerospace industry is being developed by the Metal Improvement Company (MIC), Derby UK, and the Lawrence Livermore National Laboratory (LLNL), part of the University of California. The technique, known as lasershot peening uses LLNL's solid state laser to give repeated "shocks" to the surface of the material, improving the material's tensile strength and crack resistance properties.
The lasershot peening technique works by generating a plasma at the surface of the material. Laser intensities of 200 Joules per square centimetre in a pulse lasting 30 nanoseconds can generate shock pressures of up to 109 atmospheres when absorbed on a metal surface. The precise depth of residual stress introduced into the surface can be controlled by applying successive shocks to the same area, driving the residual stress progressively deeper without damaging the material at the surface.
Deep residual stress is important for safety critical components such as turbine blades in aeroplane engines. Tests on lasershot peened turbine blades have so far shown that the surface engineering technique has a marked effect upon the properties of the material. On two lasershot peened blades, V-shaped notches were cut 3.8mm into the material. After 10 million cycles of the blade at optimum speed and vibration no cracks were detected in the material, demonstrating a high level of fatigue resistance in the critical surface area. In tests with blades with 6mm notches, the fatigue strength of the blades was more than double that of conventionally shot peened steel.
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Notes For Editors
- This item is due to appear as "Lasershot Peening Comes Out Of The Lab" by Graham Hammersley, Manager of Technical Services at Metal Improvement Company, in the May issue of Materials World, Volume 7, Issue 5, p.281
- 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.
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