Energy-based modeling of ultra high-pressure waterjet surface preparation processes including milling, peening, and texturing applications

An in-depth study into the use of ultra high-pressure (UHP) waterjets (WJ's) for the surface preparation of advanced materials was performed. In all, the functionality of waterjets at pressures extending to 600 MPa was evaluated for (i) surface texturing, (ii) material removal, and (iii) subsurface modification of a titanium alloy. Additional studies considering aluminum alloys were also performed. A semi-empirical energy-density model governing the centerline kerf depth when a metallic substrate is impinged by a waterjet was presented, and empirical validation showed strong correlation. The basis of the model suggested that a material exhibits a threshold energy density, below which erosion is not initiated. By characterizing the energy density transferred to the workpiece, the process conditions can be divided into two groups: those that induce residual stress with minimal surface modification and those that lead to bulk material removal.;Further studies were explored based upon these two groupings. A peening study was performed on a Ti-6A1-4V titanium alloy. The results of the study highlighted that compressive residual stress levels up to 80% of the material yield strength could be introduced at the shallow surface layers. Still, the resulting stress gradients were extremely steep---with low residual stress levels detected at depths greater than 0.030 mm below the surface. Fatigue samples were processed based on the optimal conditions selected by considering the resulting surface roughness and residual stress. The fatigue study showed that waterjet peening of a Ti-6A1-4V titanium alloy exhibited minimal impact on the fatigue performance; while a cast aluminum alloy showed a 40--60% increase in endurance limit. A second independent study was performed to characterize the feasibility of the UHP-WJ for the removal of an alpha case layer from Ti-6A1-4V titanium alloy. The waterjet proved capable of fully removing the alpha case layer---although the results of the study suggest further optimization is still required. This comprehensive study provided an innovative look at the material processing alternatives for the waterjet---and the results suggest a strong feasibility exists for controlled surface preparation of metallic substrates.