Laser Peening and Laser Peenforming: New Tools for Inducing Surface Stress

摘要

Laser peening is newly emerging as an important commercial technology for inducing deep levels of residual compressive stress precisely and over large surface areas of metal components. The technique has important applications for treating components to improve fatigue lifetime and/or resistance to stress corrosion cracking. A new important and related technology, laser peenforming, uses deeply applied compressive stress to elongate treated surfaces and thus induce large curvature and precise shape in thick metal panels. It can also he used to straighten components with precisely placed residual stress. The current practice of shot peening and other methods exploits compressive residual stress in a surface layer to extend service lifetime in fatigue and corrosion-prone parts. Since tensile stress is required for initiated cracks to grow, inducing residual compressive stress in a surface prone to cracking retards crack growth. This approach is very important in parts subjected to cyclic loads, where failure is due to fatigue, or to a corrosive environment, where cracks grow via stress corrosion cracking. Several mature processes induce compressive surface residual stress, including peen hammering, cold rolling, and shot peening. These processes have proved to be beneficial and are widely employed. However; they are limited in their ability to introduce compressive stress as deeply or as precisely as desired with the result that they often do not improve component service life as much as needed. The laser peening process overcomes the limitations of other peening technologies by reliably and precisely introducing very deep levels of residual stress with excellent post-peen surface quality, thereby offering significantly better improvements in service lifetime.