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Practical evaluation and accurate prediction of edge cracking are challenging issues in stamping AHSS for automotive body structures. This paper introduces a new hole-expansion testing method that could be more relevant to the edge cracking problem observed in stamping AHSS. A new testing method adopted a large hole diameter of 75 mm compared to the ISO standard hole diameter of 10 mm. A larger hole diameter was determined to be sensitive to edge cracking using the finite element method (FEM) based sensitivity analyses with various hole sizes. A die punching tool was developed to replicate typical production blanking conditions. An inline monitoring system was developed to visually monitor the hole edge cracking during the test and synchronize with the load-displacement data. Two AHSS materials, DP980 and TRIP780, and an aluminum alloy, A1 5182-O, were experimentally evaluated.

Practical evaluation and reduction of edge cracking are two challenging issues in stamping AHSS for automotive body structures. In this paper, the effects of the shear clearance and shear rake angle on edge cracking were investigated with three different grades of AHSS; TRIP780, DP 980, and DP 1180. Five different shear clearances, between 5% and 25% of material thickness, were applied to the flexible shearing machine to generate samples for the half specimen dome test (HSDT). The shear loads and the shear edge quality were thoroughly characterized and compared. The HSDT created the edge forming limits as compared to the base material forming limit diagram. The load-displacement curve was acquired by the load-cell and the strain distribution was measured using a digital image correlation (DIC) system during the dome test.

The automotive industry applies Laser Welded Blanks (LWB) to increase the material utilization and light-weighting of the vehicle structure. This paper introduces a novel tensile testing method to characterize the hardening behavior of the weld material with a digital image correlation (DIC) and apply it as a constitutive hardening model in forming simulations with the LWBs of GEN3 steel. Formability tests under biaxial conditions were performed with LWB of GEN3 steel. Experimental results were correlated with finite element analysis (FEA) predictions that were conducted with and without the weld material model. The results show the weld material model for the LWB improves the accuracy of FEA predictions of both necking failures on the base metal as well as cracking on the weld.

Nondestructive Evaluation (NDE) techniques are widely used in the manufacturing industry to control the quality of materials or final products. In the automotive industry, eddy current (EC) testing is one of the most extensively used NDE techniques for automatic in-line inspection of ferrous materials such as advanced high strength steels (AHSS). In addition, shearing is a very common forming operation in the automotive industry. With the increase of shearing clearance, the sheared-edge experiences significant work-hardening that normally decreases the formability of the sheared edge. In this paper, a novel, real-time monitoring NDE method based on the EC sensor was developed to characterize variations in shear edge quality for a DP980 steel. The developed NDE method was applied to scan the edges sheared at various clearances between 5% and 25% of the material thickness. The signal received was correlated with pre-straining introduced during the shearing process at various clearances.

As the automotive industry increasingly adopts Advanced High Strength Steel (AHSS) for the vehicle light-weighting and crashworthiness, the edge cracking significantly increases in stamping AHSS. Different lab-scale test methods such as the ISO standard hole-expansion test and the half specimen dome test are available to evaluate edge formability. However, none of these lab-scale testing methods emulates production conditions such as various shear clearances, part complexity, and shearing speed associated with the mechanical or hydraulic press operation. To address these limitations of the available testing methods, a new punching and stamping test was developed. This paper introduces the simulation and experimental approach in developing this unique testing method to design the peanut-shaped hole that is sensitive to edge cracking in stamping.