Springback of thick sheet AHSS subject to bending under tension

The springback behavior of four advanced high-strength sheet steels (Dual-Phase, TRIP, ferrite-bainite) with thicknesses ranging from 1.2 to 4 mm was investigated by means of the bending-under-tension (BUT) test. The applicability of several guidelines from the literature was investigated experimentally and numerically. The monotonic decrease of springback as back force increased was confirmed for this category of sheet steels, and a general trend for the non-linear influence of the tool radius was observed. The influence of numerical factors on the predicted values of springback was investigated, and conclusions and simple guidelines were drawn from the analysis with industrial sheet forming applications in mind.

► Thick sheet AHSS materials were experimentally and numerically investigated by means of bending-under-tension tests.
► Tool-radius vs thickness ratio showed a strongly non-linear effect on springback.
► Kinematical hardening consistently improved predictions but did not prove needed at large sheet tensions or large R/t ratios.
► Secondary curvature had little influence while the sheet thinning was shown to have a primary influence on springback.