CALCULATIONS OF FORMING LIMIT DIAGRAMS FOR CHANGING STRAIN PATHS

The method of calculating the shape of forming limit diagrams (FLDs) using a high-exponent yield criterion with the Marciniak and Kuczynski (M-K) analysis has been extended to include the effects of changing the strain paths and applied to aluminum alloy 2008 T4. Calculations incorporating abrupt path changes agreed with the general trends found experimentally. If the first stage of strain is under biaxial tension, the subsequent FLD shifts to the right and down with respect to the original FLD, whereas it shifts to the left and up when the first stage of strain is in uniaxial tension. Calculations introducing gradual strain-path changes, characteristic of stretching over a hemispherical dome, predict that the minimum of the FLD shifts to the right.