Considering damage history in crashworthiness simulations

Crashworthiness simulations using explicit Finite Element methods are a central part of the CAE process chain of car body development. Since crash tests of prototype cars at an early development stage are very expensive, a maximum in predictive performance of crash simulations can make a substantial contribution to a cost-efficient car development process. A central issue to ensure this, is an accurate prediction of crack formation in crashworthiness simulations. As the use of advanced high-strength materials in modern car body structures is increasing, crack formation is more likely to occur in such parts of the body-in-white. Typically, structural parts of a car body are manufactured by means of deep-drawing processes. Due to this, the local properties of these parts can be changed remarkably compared to the unprocessed material. In order to be able to accurately predict crack formation, the damage history including local plastic strain and pre-damage has to be considered. Since the use of forming simulations has become usual practice for sheet metal manufacturing, a damage model suitable to be used for both forming and crashworthiness simulations will be presented in the following. Based on the well-known failure criterion of Johnson and Cook, a generalized formulation is proposed that can account for complex failure modes in modern high strength materials. Numerical examples will be presented to demonstrate the practical use of the damage model for the process chain of sheet metal manufacturing.

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