Numerical and Experimental Analysis of Necking Instability in Metallic Sheets under Superimposed Stretch-Bending Loading
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Predicting the onset of localized necking is a critical challenge in sheet metal forming, particularly when complex strain paths are involved. This research investigates the influence of superimposed bending-deformation modes on the formability limits of metallic materials during stretching operations. To ensure a comprehensive analysis, three distinct materials were characterized to capture a wide range of plasticity and fracture behaviours. The study integrates a dual approach: experimental stretch-bending tests and advanced numerical simulation. Initial material characterization was conducted following ISO 12004 standards to establish a baseline for formability. Subsequently, the localization process was monitored during stretch-bending experiments using various detection criteria. These experimental results serve as the foundation for developing precise constitutive material models. Utilizing Finite Element Analysis (FEA), the insertion of bending components into the stretching process was numerically reproduced to evaluate its effect on the strain-path evolution and necking delay. The findings delineate the validity limits of standard Forming Limit Curves (FLCs) when bending is present and highlight the necessity of advanced numerical strategies to predict failure in complex forming processes.