Bending under tension is an important deformation mode during stamping and has been observed to limit achievable ductility for high strength steels. This paper presents experimental results from Angular Stretch Bend (ASB) testing, which has been used to characterize bending under tension behavior for several conventional, advanced high strength steels and ultra-high strength steels. Steels that were studied include Bake Hardenable steels, High Strength Low Alloy (HSLA) steels, Dual Phase (DP) steels, Transformation Induced Plasticity (TRIP) steels, and tempered martensitic steels. Failure heights were determined under sample lockout conditions for different punch radii. By comparing absolute formability measured by the failure height, the results can be used to provide material formability ranking for different R/t ratios. For small R/t values, bending under tension formability is a strong function of the R/t ratio and saturates at higher R/t values. Location of failure moves from the punch nose to the sidewall at higher R/t ratios for all steels except most DP steels. Most DP steels exhibit punch failure even at the highest R/t ratio indicating that bending continues to limit achievable formability. In addition, strain distributions were analyzed to provide bending under tension forming limits for the different steel grades. A procedure for isolating stretch bend performance as defined by the stretch bendability index was developed. The maximum value of the stretch bendability index is 1. For non-DP steels, the trend for the stretch bendability index as a function of R/t ratio was linear. The R/t ratio corresponding to a stretch bendability index of 1 was defined as the critical R/t ratio. For DP steels, the trend for stretch bendability index as a function of R/t ratio was non-linear. This information will be useful in the development of die design and processing strategies for high strength sheet steels.
Stretch bendability of advanced high strength steels
2003
9 Seiten, 16 Bilder, 1 Tabelle, 7 Quellen
Conference paper
English
Bake-Hardening-Stahl , Biegeelastizität , Biegeumformen , Dualphasenstahl , Formbarkeit , hochfester niedrig legierter Stahl , hochfester Stahl , Materialbruch , plastische Verformung , Plastizität , Spannungs-Dehnungs-Diagramm , Stanzen , Streckbarkeit , Streckziehen (Metall) , Verformungsfähigkeit , vergüteter Martensit
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