EFFECT OF CHANGING STRAIN PATHS ON FORMING LIMIT DIAGRAMS OF AL 2008-T4

The effect of changing strain paths on forming limits of aluminum alloy 2008-T4 has been investigated by determining forming limit diagrams (FLDs) after prestraining. Sheets were prestrained to several levels in uniaxial, biaxial, and plane-strain tension parallel and perpendicular to the prior rolling direction (RD). Abrupt changes in the strain path can be used to increase the forming limits. Prestraining in biaxial tension generally lowers the forming limits for the entire FLD, whereas prestraining in uniaxial tension raises the limits on the right-hand side of the FLD without much effect on the left-hand side. Prestraining in plane-strain tension raises both sides away from the minimum. Finally, it was found that after prestraining, the amount of the additional plane-strain deformation possible depends on the effective strain during prestrain.