Advanced Manufacturing Laboratory    



Micro-scale Laser Shock Peening (micro-LSP) and Micro-scale Laser Peen Forming (micro-LPF)


Micro-scale Laser Shock Peening (Micro-LSP) and Micro-scale Laser Peen Forming (Micro-LPF)

Laser shock processing (LSP) involves laser-induced, medium-confined plasma sending strong shock waves into target and thus imparting compressive residual stress into surface layer to improve fatigue performance.  Compared with mechanical shot peening, LSP offers a deeper layer of compressive residual stress, and is more flexible especially for irregular shapes.  It has been shown that LSP can improve fatigue life by 5 to 6 times.  LSP was proposed by Dr. Allen Clauer of Battelle Institute in 1960s but requires powerful lasers to general several to tens GW/cm2 laser intensity.  Prof. Fabbro’s group in France was responsible for many advances in LSP. 

We at Columbia University have been carrying out investigations on micro-scale LSP, where the laser beam spot size is in the order of tens of microns instead of in mm scale as in the previous studies.  The motivation is (1) to enable less powerful and thus less expensive laser to be used, and (2) to enable micro-devices to have the same benefits as their macro counterparts.  Since the beam spot size now is in the same order of magnitude as the grain size of the material to be peened, the material behaves anisotropically.   Our strategy has been to use single crystal materials for our experimental and numerical investigations.  Single crystal plasticity and rate-dependent flow stress models are implemented in the numerical models.  We also carried out an extensive investigation of spatially resolved residual stress characterization using the micro X-ray diffraction technique.  This is done in collaboration with the National Synchrotron Light Source at Brookhaven National Laboratory.

More recently, LSP has been extended to LPF (laser peen forming), in which the target is shaped (say, bent) and at the same time imparted desirable residual stress on BOTH sides of the target.  In mechanical bending, there is compressive residual stress on one side of the specimen only.  Lawrence Livermore National Lab has reported progress in LPF and our work focuses on using a micron-sized laser beam to affect LPF.