Edge crack evaluation in laser-polished AHSS via Diabolo test and multi-scale simulation

Abstract Dual-phase (DP) steels, particularly DP1000, are widely used in the automotive industry due to their excellent strength-ductility balance and crash performance. However, their high tendency to develop edge cracking during manufacturing processes such as blanking and trimming remains a significant challenge. This issue arises primarily from the sharp mechanical property contrast between the ferritic and martensitic phases. As a countermeasure, laser-polishing has been introduced to enhance edge quality by locally remelting and smoothing the cut surfaces, thereby eliminating burrs and micro-defects. This study investigates the effectiveness of laser-polishing in improving edge formability using a novel Diabolo test setup, which promotes pronounced deformation at the specimen edge due to its hourglass-shaped punch geometry. Experiments are conducted on 1.5 mm thick DP1000 sheets with varying edge morphologies, and surface strain evolution is captured using digital image correlation (DIC). To complement the experiments and gain insight into the multiple mechanisms behind the enhanced performance, a multi-scale simulation approach is applied. The model integrates the actual mechanical properties and topographical features of the laser-polished edge, incorporating both macroscopic and microscopic effects, including a calibrated surface factor. Results reveal a notable improvement in edge formability and global formability in laser-polished specimens compared to sheared specimens. The numerical predictions show both excellent agreement with the experimental force-displacement curves as well as strain fields.