Prediction of limiting strains and fracture toughness of deep drawing quality steel using stretching and incremental forming processes

Products made of sheet metal are widely used in aerospace, automotive, and architecture due to their lightweight, strength, and formability. However, unexpected fractures during forming pose a challenge. This research paper examines the fracture thresholds of deep drawing quality steel sheets by utilizing both forming limit diagrams and fracture forming limit diagrams, which were developed through stretching and incremental sheet forming. Oyane's damage model predicts theoretical fracture limits, aligning with experimental incremental sheet forming results within a 7.47 % error. Fracture toughness, measured via double notched tensile tests and incremental sheet forming, shows a strong correlation (R = 274.2 kJ/m 2 and R = 280.2 kJ/m 2 , respectively). Hemispherical cups were formed using single and multi‐stage incremental sheet forming, with multi‐stage strategies mitigating failures observed in single‐stage forming. In multi‐stage shaping, a novel theoretical model forecasts sheet thickness. Experimental testing and finite element simulations are conducted to analyze forming forces and deformation energy. Fractographic analysis confirms ductile failure, as evidenced by the presence of dimples and voids.