A Novel Method to Nondestructively Measure the Shear Edge Properties for Edge Cracking Evaluation with Advanced High Strength Steels

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. Microhardness measurements were taken to compare the trends obtained from the NDE tool with the hardness values. To evaluate the edge formability, half-specimen dome testing (HSDT) was conducted for the edges sheared at various clearances. A digital image correlation (DIC) system was used to record deformation during the HSDT. The failure strain of sheared edges was correlated with the NDE measurements for each clearance to assess the application of an NDE measurement in determining edge quality. The developed NDE method has great potential for significant financial and technical impact on blanking and piercing operations for blank processors or stampers, particularly for AHSS.