Measure of Forming Limit Strain on the Aluminum Sheets Passed Through Draw-Bead by Digital Image Correlation

Accurate determination of the forming limit strain of aluminum sheet metal is an important topic which has not been fully solved by industry. Also, the effects of draw beads (enhanced forming limit behaviors), normally reported on steel sheet metals, on aluminum sheet metal is not fully understood. This paper introduces an experimental study on draw bead effects on aluminum sheet metals by measuring the forming limit strain zero (FLD₀) of the sheet metal. Two kinds of aluminum, AL 6016-T4 and AL 5754-0, are used. Virgin material, 40% draw bead material and 60% draw bead material conditions are tested for each kind of aluminum. Marciniak punch tests were performed to create a plane strain condition. A dual camera Digital Image Correlation (DIC) system was used to record and measure the deformation distribution history during the punch test. The on-set necking timing is determined directly from surface shape change. The FLD₀ of each test situation is reported in this article. From the results of this study, the draw bead effects (enhanced forming limit behaviors) are found in both aluminums tested. Basic theory, experiment plan, experimental setup, test results and data analysis are shown in detail in this paper.