SUBJECT: Ph.D. Dissertation Defense
BY: Andrea Marcon
TIME: Friday, January 20, 2017, 10:00 a.m.
PLACE: MARC Building, 114
COMMITTEE: Prof. Shreyes Melkote, Chair (ME)
Prof. Minami Yoda (ME)
Prof. Richard Neu (ME)
Prof. Christopher Saldana (ME)
Dr. James Castle (The Boeing Company)


Shot peening is a cold working process used in industry to improve the fatigue and corrosion resistance of metal components. Spherical shots (metal, ceramic or glass) impact the metal surface with sufficient energy to cause localized plastic deformation, consequently introducing beneficial compressive residual stresses in the surface layer. However, this technique is also characterized by high consumables cost, workpiece contamination and undesired surface roughening. Water Cavitation Peening (WCP) is one of the alternative techniques recently developed in the effort to overcome the limitations imposed by shot peening. The basic concept involves creating a cavitation cloud by injecting a high speed liquid jet into a low speed liquid jet (co-flow configuration), and placing the workpiece at an optimum distance from the nozzle. The unstable vapor-filled bubbles forming the cavitation cloud release shock waves upon collapsing that propagates through the workpiece. By suitably controlling the flow parameters and nozzle dimensions, it is possible to produce a sufficiently aggressive cavitation cloud capable of plastically deforming metal surfaces and introducing beneficial compressive residual stresses with very limited surface roughening. A novel system was developed to experimentally investigate the WCP process in co-flow configuration. The flow was characterized by means of accelerated erosion tests, strip curvature tests, high speed video imaging and residual stress measurements on Al 7075-T651. The same methodology was also used to investigate the effect of nozzle geometry on the cavitation intensity in WCP. Finally, pitting tests were conducted to investigate the interaction between the cavitating flow and the material surface, and a 2D numerical model for the estimation of residual stresses was developed. The thesis presents the underlying scientific basis needed to develop the next generation of production-grade, large scale cavitation peening machine tools for aerospace applications. The characterization of the process and the nozzle will serve as a basis for users to select optimal processing parameter and create a cost effective alternative to the currently employed methodology. This project is funded by Boeing Research and Technology (BR&T).