Evoution of Yield surfaces: Past and Future Trend - Part 1

It is essential to know the amount of springback for a given forming process, so that the process or the design of the tool can be modified to obtain the desired product shape. This requires a comprehensive understanding of loading and unloading processes, and determination of elastic constants with finite plastic deformation which, in turn, require precise determination of subsequent yield surfaces.
            The comprehensive experimental work on the yield surfaces was first performed by Phillips’s group (Phillips et al., 1972, 1974; Phillips and Tang, 1972; Phillips and Ricciuti, 1976; Phillips and Moon, 1977; Phillips and Lee, 1979; Phillips and Chong, 1979; Phillips and Lu, 1984) on pure annealed aluminum. However, most of the work was done for less than 2% plastic strain. Stout et al. (1985) had concluded that the small scale yielding was controlled by dislocations; whereas, the large scale yielding was controlled by texture evolution after moderate strains.
         In the present study (references below) a comprehensive set of experimental results on the initial and subsequent yield surfaces in Al 6061-T6511 (a very low work hardening aluminum alloy)  based on 10µε deviation from linearity definition of yield, are presented. The subsequent yield surfaces are determined during tension, free end torsion, combined tension–torsion, and tension- tension space after reaching different levels of strains. The yield surfaces are also obtained after linear, bi-linear and nonlinear unloading paths after finite plastic deformation.

 References:

Evolution of subsequent yield surfaces and elastic constants with finite plastic deformation. Part-I: A very low work hardening aluminum alloy (Al6061-T6511)  

International Journal of Plasticity, Volume 25, Issue 9, September 2009, Pages 1611-1625
Akhtar S. Khan, Rehan Kazmi, Amit Pandey, Thomas Stoughton