The Woodruff School

SUMMARY

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 Jet 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 in a quiescent water tank, 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.
The specific objectives of the proposed research are to: (1) Design and fabricate a WCP system (not commercially available), (2) experimentally characterize the material response to the process parameters, (3) experimentally characterize the nozzle effect on the process capabilities, (4) model of residual stresses from stress-strain analysis of individual pits.
It is expected that the proposed research will create 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).

SUBJECT:	Ph.D. Proposal Presentation

BY:	Andrea Marcon

TIME:	Friday, April 3, 2015, 1:00 p.m.

PLACE:	MARC Building, 114

TITLE:	Water Cavitation Jet Peening for Aerospace Materials

COMMITTEE:	Dr. Shreyes Melkote, Chair (ME) Dr. Minami Yoda (ME) Dr. Richard Neu (ME) Dr. Christopher Saldana (ME) Dr. James Castle (The Boeing Company)

SUMMARY 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 Jet 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 in a quiescent water tank, 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. The specific objectives of the proposed research are to: (1) Design and fabricate a WCP system (not commercially available), (2) experimentally characterize the material response to the process parameters, (3) experimentally characterize the nozzle effect on the process capabilities, (4) model of residual stresses from stress-strain analysis of individual pits. It is expected that the proposed research will create 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).