The use of digital processing in studying stretch-forming sheet metal

A Finite Element Analysis of a Tapered Flat Sheet Tensile Specimen

“…It seems that a more productive approach of obtaining a better estimate of plastic stress-strain curve for ductile sheet metals using a tapered tension coupon is to find an effective correction method for the estimated stress-strain curve based on ε 3 . Traditionally, the Bridgman correction method based on the certain assumption of the neck geometry may be used [10,11] but it requires the additional measurements of geometric parameters of the neck. Another method is an iterative correction method proposed by Tao et al [15] that may be used here as well but it needs the repeated finite element analyses and post-data processing steps.…”

“…The parameters k; R 0 ; R 1 ; and b used by the ANSYS finite element program can then be obtained via equation (11). Five different materials (two base metals D600a and D600b, two heat-affected zones HAZ_a and HAZ_b, and one weld metal) made of a dual-phase steel sheet were examined in this study.…”

“…Using proper image magnifications and decorated surface contrast patterns, large plastic strains and high strain gradients over gage dimensions as small as only a fraction of the original sheet thickness within the necking region in a thin sheet can be easily mapped out in great detail [18,20]. The availability of such local plastic surface strain measurements by digital image correlation provides both a direct experimental estimate on the upper and lower bounds of the post-necking effective plastic stress-strain curves [6,21,22] and an improvement on the accuracy and reliability of some analytical or numerical methods in further correcting the post-necking effective stress-strain curves [11,14,15].…”

“…An experimental technique called digital image correlation (DIC) has been increasingly used in recent years for whole-field surface strain mapping applications in sheet metal testing, in part, due to a wider availability of many inhouse and commercial software tools [11,[16][17][18][19][20]. Using proper image magnifications and decorated surface contrast patterns, large plastic strains and high strain gradients over gage dimensions as small as only a fraction of the original sheet thickness within the necking region in a thin sheet can be easily mapped out in great detail [18,20].…”

“…Although the standard uniaxial tension test is often used to obtain the basic mechanical properties of the steel sheet metals, the valid plastic stress-strain data obtained for those low-strain hardening but ductile materials are rather limited to small strain ranges (say, a few percent) due to the earlier onset of the diffuse necking [8,9]. Some analytical and numerical methods have been developed over the years to address the problem of estimating the effective plastic stress-strain data beyond diffuse necking using a standard ductile metal tension coupon with certain corrections [10][11][12][13][14][15].…”