Laser peening or laser shock peening is a relatively new industrial process to enhance the fatigue lifetime of components. For this purpose compressive stresses are created in the material to counteract the fatigue caused by tensile stresses. The classical approach is shot peening with small spheres which has two main disadvantages. Firstly the material is contaminated by the physical contact and secondly the created stresses have a very limited penetration depth.
To overcome these limitations laser shock peening was invented. Laser shock peening creates the shock wave with the help of a high energy laser pulse. The pulse hits the target and creates a plasma. The plasma expands and thus creates a shock wave. To increase this effect the material is often coated with an opaque layer that absorbs the laser pulse and with a transparent layer (often water) that transmits the laser pulse but locally confines the palsma which increases the depth and intensity of the shock wave.
The following video of the company Litron Lasers shows the principle:
Materials that were laser peened show a ten times increased fatigue life time compared to parts without peening. This opens up opportunities for new materials especially in harsh environments.
Laser Peening can be put in three categories:
- High energy, low repetition rate lasers operating typically at 10-40 J per pulse with 8-25 ns pulse length. 0.5 – 1Hz rep rate, nominal spot sizes of 2 to 8 mm.
- Intermediate energy, intermediate repetition rate lasers operating at 3-10 J with 10-20 ns pulse length. 1 - 10Hz rep rate, nominal spot sizes of 1–4 mm.
- Low energy, high repetition rate lasers operating at ≤ 1 J per pulse with ≤10 ns pulse length, 60+ Hz rep rate, ≤ 1 mm spot size.
With the current laser technologie laser peening is most the time performed with intermediate or low pulse energies. The LPY and TRLi series of Litron Lasers are a good choice for this application due to their high pulse energies with exceeding stability and very low maintenance.