GRAHAM WARWICK / WASHINGTON DC
Curtiss-Wright company Metal Improvement has commercialised a laser peening technology originally developed by the USA's Lawrence Livermore National Laboratory (LLNL). The Lasershot process is being used to increase the life of blades used in Rolls-Royce Trent 500 and 800 engines.
In conventional peening, components are bombarded with metal shot to induce a layer of compressive stress at the surface that resists fatigue and corrosion. Laser peening uses short bursts of intense light that create a high-pressure plasma on the surface. A tamping layer confines the plasma and drives the pressure pulse into the metal.
The laser-induced shock waves can create a residual compressive stress over 1mm (0.04in) deep, four times the depth obtained with shot peening. The deeper level of compressive stress provides greater resistance to fatigue and corrosion, says Metal Improvement. Laser peening can be "surgically" applied to place compressive stress in areas vulnerable to crack propagation, says LLNL.
Laser peening was invented in the 1970s, but the high cost and slow speed of lasers delayed its commercialisation. Metal Improvement is using an LLNL-developed neodymium-doped glass lasers that produce 1 billion W of peak power in 20-billionth of a second bursts, putting 100J/cm2 of energy into the metal. With 125W average power, the laser can fire five pulses a second, compared with one pulse every 4s for the best commercially available lasers, says LLNL.
Metal Improvement's facilities in Livermore, California and Earby in the UK each have two laser peening systems. Other applications are under development for Rolls-Royce.
Source: Flight International
