Recent advances in Abrasive Waterjet (AWJ) technology have resulted in a new process for surface treatment that is capable of introducing compressive residual stresses and a surface texture that facilitates bonding. The current research focuses on quantifying the influences of Abrasive Waterjet Peening (AWJP) with elastic prestress on the surface and subsurface residual stress distributions and surface texture of three engineering metals (ASTM 228, Ti6Al4V and inconel 718).

A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the treatment parameters with primary contributions to the residual stress field. The applied elastic prestress ranged from 0 to 75% of the target yield strength. Surface residual stress resulting from AWJP was compressive and ranged from 500 to 2500 MPa, and the depth of compressive residual stress ranged from nearly 80 to 600 μm. While the elastic prestress had no effect on the surface texture, it was a primary contributor to the magnitude of surface residual stress, which increased with an increase in the elastic prestress. The boundary conditions used to apply the prestress were found to be important to the residual stress field. Load control flexure prestress resulted in larger surface and subsurface compressive residual stress when compared to the displacement control flexure prestress.

A finite element analysis of the treatment was used to explore the potential for using alternate prestress configurations to improve the residual stress distributions and to develop an understanding of the treatment mechanics. Three different prestress conditions (flexure, axial and biaxial loading) were simulated on a Ti6Al4V target subjected to a single impact. Each condition was studied under both load and displacement control boundary conditions. The finite element evaluations identified two mechanisms (plasticization and superposition) that contributed to the increase in magnitude and changes in shape of the residual stress field in treatments with elastic prestress. Overall, application of elastic prestress resulted in a 100% and 40% increase in the compressive surface residual stress and maximum residual stress and a 25% increase in the depth of compressive residual stress. The responses were influenced by the prestress distribution and in all cases load control prestress had a larger influence when compared to the displacement control. Results of the finite element model indicated that a biaxial prestress incorporating a combination of compressive and tensile components could be used to further improve the residual stress characteristics resulting from particle-based surface treatments.

According to the results of this study, AWJP with elastic prestress can serve as a viable method of surface treatment in situations that require an increase in surface roughness and a compressive residual stress. The current study has showed that elastic prestress could be used as a design variable to achieve a desired subsurface residual stress distribution in particle-based surface treatments.

Keywords: abrasive waterjet, elastic prestress, finite element model, residual stress.