Analytical solution of anisotropic plastic deformation induced by micro-scale laser shock peening

Abstract

Laser shock peening (LSP) is a process to improve material fatigue life by introducing compressive residual surface stress in a target. The residual stresses are introduced when a high-intensity laser impinges on an ablative layer deposited on the surface of the target material. The interaction between laser and the ablative layer creates a high pressure plasma that leads to plastic deformation. If the laser spot size is of the order of a few micrometers, the potential exists to use this process to enhance the fatigue life of micro-scale components or to selectively treat highly localized regions of macroscale components. However, for such micro-scale laser shock peening (μLSP), the laser spot size is likely to be of the order of the material grain size. Therefore the material properties must be treated as anisotropic and heterogeneous rather than isotropic and homogeneous. In the present work, anisotropic slip line theory is employed to derive the stress and deformation fields caused by μLSP on single crystal aluminum which is oriented so that plane strain conditions are admitted. The predicted size of the deformed region is compared with deformation measurement by atomic force microscopy (AFM) and with lattice rotation measurement by electron backscatter diffraction (EBSD). In addition, single crystal plasticity finite element simulations are performed for the process. The results suggest that the analytical solution captures the salient features of the deformation state and is able to predict the size of the resulting plastically deformed region.