Hardening and Final Thickness Data Used in the Quasistatic Nonlinear Analysis of Stamping Parts

Abstract

During the development stages of automotive products, the use of numerical simulation tools to evaluate the structural performance of a particular component is essential, since it avoids spending on trial and error, reducing design time while optimizing the shape and function of the component. Most of these numerical simulation tools are based on finite element techniques, with appropriate formulation to solve linear static, dynamic linear, quasi-static non-linear and nonlinear dynamic (impact). Among the tests quasi-static non-linear can cite the simulations of indentation and contact known in the automotive sector such as "palm-printing", "oil-canning" and "elbow-dimpling". These analysis simulate a situation of contact between a given indenter (with different formats) and the external surface of a vehicle component, involving material nonlinearities (plasticity), boundary nonlinearities (contact) and possibly geometric nonlinearities (large displacements and buckling). These external components may be parts of the body as well as fenders, doors and hood. In these simulations, typically are used finite element methods where the sheet metal is modeled with Kirchhoff plate element, with implicit integration for the load and robust formulations enough to consider the presents nonlinearities. Among the main geometric and material input data of the problem, it takes the thickness of the component and the stress-strain curve of material. These data are obtained through tests on specimens of the flat plate (data from the rolling process). External components of an automotive body are manufactured from a stamping of sheet metal plane resulting in a final product with variable thickness due to different levels of stretch and a heterogeneous distribution of residual plastic strain. Generally, these informations are not considered in numerical simulations of the product and may cause considerable errors in the analysis of stamped parts involving nonlinearities. This study aimed to simulate an event called palm-printing in an automobile fender, with and without the consideration of the final data of the numerical simulation of the stamping process (final thickness and residual plastic strain per element) and the results compared with those obtained experimentally. Results showed that the consideration of stretching and hardening from the stamping process can improve the correlation of final results in analysis involving small material and geometric nonlinearities.