ABSTRACT--The compression test of a ring is customarily used to determine the friction coefficient in metal-forming problems. The aim of this paper is to describe a procedure to obtain, for metals in the large deformation range, the stressstrain curve and friction coefficient through the same test. The friction coefficient is evaluated by comparing curves obtained by a finite element code with the experimental curves. The stress-strain curve is obtained by inverting an analytical solution, calculated by a lower-upper-bound approach. Good results in terms of accuracy are obtained.
It has been recently demonstrated that co-flow water cavitation peening introduces beneficial compressive residual stresses in aerospace materials. In this process, cavitation is produced in the shear layer between two concentric co-flowing water jets with a large velocity difference. Although prior studies have shown that material response is greatly influenced by the jet velocities and standoff distances used, no effort has been made to explain the observed trends by correlating the salient features of the cavitating flow with the resultant process performance. This article investigates the effect of jet velocities in co-flow water cavitation peening through high-speed imaging and surface-pitting tests on Al 7075-T651 alloy. High-speed imaging is used to determine the cavitation cloud width as a function of the inner and outer jet velocities. Results show that the observed increase in mass loss with inner jet velocity (Vin) is due to a corresponding increase in cloud width. The high-speed imaging results also highlight the trade-off between the cloud width and the cloud occurrence probability at different outer jet velocities Vout. While a lower Vout yields a larger cavitation cloud width, a higher outer flow velocity sustains the cavitation for a larger distance, resulting in more cavitation impacts on the material surface. As a result, for the range of inner jet velocities considered, an optimum value for the outer flow velocity (Vout = 11.0 m/s) is shown to exist, which is confirmed by mass loss and strip curvature measurements. Surface micropitting analysis is used to evaluate the cavitation intensities at different flow conditions. The combined pitting and high-speed imaging results explain why higher cavitation loads are produced at the optimum flow conditions of Vin = 150 m/s, Vout = 11.0 m/s, and sn = 45.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.