|Laser peening induces deep compressive stress, which significantly extends part life over any conventional treatment.|
Lawrence Livermore National Laboratory (LLNL) researchers and Metal Improvement Co. Inc., Paramus, N.J. (www.metalimprovement.com), developed a surface-heating technology said to lengthen the life of critical metal parts for commercial aircraft.
The technique uses advanced laser peening and shock generation technology to impart deep compressive residual stress, making components more resistant to fatigue stress. Traditionally, metals are shot-peened by bombardment with tiny metal balls. This induces a layer of compressive stress at the surface that prevents metal fatigue and reduces corrosion.
Ordinary laser peening has been around since the 1970s and uses short bursts of intense laser light to create pressure pulses on the metal surface. The pulses generate shock waves that travel into and compress the metal. But the technology has not been practical for commercial parts because of high costs and slow lasers.LLNL researchers developed a neodymium-doped glass laser that produces 1 billion W of peak power, about the output of a large commercial power plant, in 20 billionth of a second bursts.
With 125 W of average power, the laser can fire five pulses per second compared with one pulse every 4 sec for commercially available lasers. Also, the LLNL laser creates compressive stress to a depth of 0.04 in. beneath the surface, about four times deeper than conventional shot peening.
Laser peening may find use in upgrading commercial aircraft components such as discs, landing gears, bulkheads, and drive gears. The technology could also be a candidate for the automotive and truck industries.