A Benchmark Test for Springback: Experimental Procedures and Results of a Slit-Ring Test

Experimental procedures and results of a benchmark test for springback are reported and a complete suite of obtained data is provided for the validation of forming and springback simulation software. The test is usually referred as the Slit-Ring test where a cylindrical cup is first formed by deep drawing and then a ring is cut from the mid-section of the cup. The opening of the ring upon slitting releases the residual stresses in the formed cup and provides a valuable set of easy-to-measure, easy-to-characterize springback data. The test represents a realistic deep draw stamping operation with stretching and bending deformation, and is highly repeatable in a laboratory environment. In this study, six different automotive materials are evaluated. They included one aluminum alloy (AA6022-T4), one deep drawing quality and special killed (DQSK) mild steel, one bake hardenable (BH) medium strength steel, a conventional high-strength low-alloy (HSLA) steel, and two advanced high-strength steels (AHSS) represented by one dual-phase (DP) steel, and one TRansformation Induced Plasticity (TRIP) steel. A particularly interesting aspect of this experiment is the direct measurement of residual stresses by diffractive stress analysis in collaboration with NIST Center for Neutron Research, and is believed to be the first application of this technique to sheet metal forming. Complete material data and experimental results are documented, including punch force trajectories, amount of draw-in, ring opening displacement, axial and hoop stresses before and after the rings were slit. The data is ideal for the evaluation and improvement of current forming and springback simulation capabilities. Efforts for the correlation of simulation with the obtained experimental data are underway and will be reported in follow-up studies.