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The present study deals with both numerical and experimental evaluation of failure strain and fracture pattern during shock tube impact forming of 1.5 mm thick AA 5052-H32 sheet. A hemispherical end nylon striker is propelled to deform the sheet at different velocities. Here the main objective is to understand the effect of flow stress models and fracture models on the forming outputs. The experimental situation is modelled in two stages, i.e., incorporating the pressure in the first stage, and displacement of the striker in the second stage in finite element simulation using the finite element (FE) code (DEFORM-3D). A new strategy followed to evaluate the rate-dependent flow stress data from the tensile test of samples sectioned from shock tube-based deformed sheet is acceptable, and finite element simulations incorporating those properties predicted accurate failure strain and fracture pattern. Out of all the flow stress models, the modified Johnson-Cook model has a better flow stress predictability due to the inclusion of the non-linear strain rate sensitivity term in the model. During the prediction of the failure strain and necking location, Cockcroft-Latham failure model, Brozzo failure model, and Freudenthal failure model have a fair agreement with experimental data in combination with the two flow stress models, i.e., Johnson-Cook model and modified Johnson-Cook model.

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In the present study, a high-velocity sheet metal forming experiment has been performed using a hemispherical end nylon striker inside the shock tube. The striker moves at a high velocity and impacts the sheet mounted at the end of the shock tube. Three different velocity conditions are attained during the experiment, and it helps to investigate the forming behavior of the material at different ranges of velocity conditions. Various forming parameters such as dome height, effective strain distribution, limiting strain, hardness, and grain structure distribution are analysed. The dome height of the material increases monotonically with the high velocity. The effective-strain also follows the similar variation and a bi-axial stretching phenomenon is observed. The comparative analysis with the quasi-static punch stretching process illustrates that the strain limit is increased by 40%-50% after the high-velocity forming. It is because of the inertial effect generated on the material during the high-velocity experiment, which stretches the sheet further without strain localization.