FE Simulation and Full-field Strain Measurements to Evaluate the Necking Phenomena

During airbag production, many parts are obtained by plastic deformation such as the lid of the gas generator. Since the airbag gas generator is a significant vehicle safety part, several pressure tests have been developed in order to prove the reliability of this product. A ductile fracture problem initialized by a localization of the deformation is observed along the blending radius. In order to understand the mechanical processes involved in the forming operation, a numerical and experimental study was developed. A tensile test specimen extracted from the sheet of study, undergoes elastic deformation that is followed by a transition to plastic deformation. Although during this stage of the test the deformation is stable, the strains begin to localize within a relatively broad zone known as diffuse necking. The stable deformation, with continuously rising load, is followed by the instability whereby a local neck or shear band is produced due to strong localization of deformation. The localization is explainable by the inhomogeneity in macroscopic material properties in the specimen. The necking behavior is a vital precursor to the final failure. A Digital Image Correlation (DIC) method is used in 2D and 3D to evaluate the necking and localization of deformation, which shows clearly the two stage of necking phenomena. Moreover, a numerical modeling was developed of tensile test under ABAQUS commercial software. In this model we use Gurson Tvergaard Needleman (GTN) ductile model of damage to predict the necking phenomenon. Furthermore the results from FE simulations are compared with experimental results from uniaxial tensile tests. Finally we develop the numerical model of the lid of the gas generator obtained by forming process