My apologies. This is Siavash's Ph.D. Final Exam-not Prelim. Best Wishes to Siavash and please consider attending his Seminar. MATERIALS ENGINEERING SEMINAR "Investigation of the Residual Stresses after Shot Peening Process" By Siavash Ghanbari Purdue MSE Ph.D. Final Exam Advisor: Professor David F. Bahr ABSTRACT Mechanical surface treatments using an elastic-plastic cold working process can develop residual stresses on the substrate or in the bulk. Compressive residual stresses increase resistance against surface crack propagation, so the mechanical performance can be improved by this technique. Compressive residual stresses can be created by different methods such as hammering, rolling, and shot peening. Shot peening is a well-established method to induce compressive residual stresses in the metallic components using cold working, and often ascribed to being beneficial to fatigue life in the aerospace and automobile industries. In this method, the surface is bombarded by high-velocity spherical balls which cause plastic deformation of the substrate, leading to a residual compressive stress after shot peening on the surface of the part. Also, there is a relationship between stress coverage on the surface and surface roughness. Shot peening influences of surface roughness, especially, the resulting surface roughness have been affected by peening size or time. Computational modeling is an appropriate and effective way which can predict the amount of produced residual stresses and plastic deformation to obtain surface roughness after shot peening simulation. In this thesis work, an experimental method to measure the magnitude of the residual stress using a nanoindentation technique was developed. The experimental method was compared to both computational predictions (in aluminum) and with x-ray diffraction measurements of stress (in an alloy steel). The current study validates the relation between nanoindentation method and numerical simulation for assessing the surface residual stresses resulted from single or multiple shot peening processes. Finally, to assess the surface roughness, a 3-D Finite Element Modeling (FEM) has been developed to compare three different shot sizes and mixed shots with simultaneous impact or sequence impacts. Date: Wednesday, September 25, 2019 Time: 3:00 P.M. Place: HAMP 2118 School of Materials Engineering Purdue University Neil Armstrong Hall of Engineering 701 West Stadium Ave. Room 2200 West Lafayette, IN 47907 765-494-4105 [PU150]