Experimental Analysis of the Strain Effect on the Anisotropic Coefficients of 6061 Aluminum Sheet Using Digital Image Processing

The anisotropy of mechanical property in sheet metals due to their rolling process causes the useful effects of increasing in drawability and harmful effects of earing phenomenon. In the present study, the variation of the anisotropic coefficient during the uniaxial tension of AA6061-O sheet has been considered using digital image correlation technique by two marking methods of regular arrays of circles and irregular accidental pattern. Meshed samples of this alloy are cut in three directions 0, 45 and 90 degrees with respect to the rolling direction and stretched by Instron test machine. During the test, transverse and longitudinal strains are measured and then by using these two parameters anisotropic parameters in different directions as more asthe planar and normal anisotropic coefficients are computed. It demonstrated that, during the straining on samples the anisotropic parameters in 0 and 45 direction showed decreasing trend and in 90 direction it has a wavy manner. The results indicated that after 10 percent elongation the normal and planar anisotropy of sheet decreased by 51% and 63%, respectively. Finally the plastic hardening behavior of sheet in different stages of the tension by using of the Hill’s quadratic yield criterion was studied and appeared that the yield surface grows totally as an anisotropic manner.