Abstracts Engineering

Residual stress fields due to laser-pulse-generated shock waves

by Scott Allen Noll

Laser shock peening (LSP) is a material processing technique that imparts compressive residual stresses, which in turn enhance the materials ability to resist crack initiation/propagation. SHOCKWAVE, a finite element program developed at The Ohio State University, is used to predict the residual stress fields for one-sided and two-sided LSP on a common industrial metal, Ti-6A1-4V. Close attention was paid to constitutive modeling, mesh refinement, and correlating the analytical results with experiments. Both one-sided and two-sided LSP techniques were analyzed for multiple peak pressures and base material thickness.The residual stress field was successfully predicted for one-sided LSP and moderately well for two-sided LSP. The challenges for two-sided LSP are discussed and a plan for further investigation is given. Plastic strains are calculated to be on the order of 1-2% penetrating to a depth of 1 to 2 mm. Compressive residual stresses at the surface are found to be 1/3 to 2/3 the yield strength of the metal. Strain rates were calculated at 106 s-1 at the front of the shock wave. To predict the residual stress, the constitutive relations must account for the effect of strain rate for one-sided LSP and also be able to model Baushinger effect for the two-sided LSP.