Markus Feucht

A Phenomenological Damage Model to Predict Material Failure in Crashworthiness Applications

The present contribution will focus on one of the most urging challenges in crashworthiness simulations, namely alternative or enhanced constitutive for-mulations to predict failure and cracking of structural parts made from high strength steel sheets. In order to achieve a more accurate prediction, the consideration of pre-damage resulting from a foregoing deep-drawing process seems to be an important extension of the proven processes. This leads to the necessity of considering damage in Finite Element Simulations of forming processes, allowing for the results to be used further on in what has to become the simulation process chain of sheet metal part manufacturing. In a broader sense, this simulation process chain may be termed as “producibility-to-serviceability”. Up to now, the driving force behind forming simulations usually is the question if a certain part may be produced on certain press equipment with a defined number of forming stages, starting from specific sheet material of given initial thickness. Carrying over the forming results to other simulation disciplines, like crashworthiness or NVH, where the serviceability of the designed structure is investigated further, will eventually give more insight into the effects of pre-straining and possible pre-damaging emerging from the production process to the target discipline. Nowadays, the crashworthiness of bodies in white is assessed to a major extent by finite element simulations without taking the production history into account. Therefore, making use of pre-damage data offers promising opportunity to the simulation engineer to enhance simulation accuracy. Regarding this, experience shows that high strength steel qualities are expected to be more problematic. The present contribution discusses engineering driven approaches to improve the predictiveness of crashworthiness simulations, and to close the constitutive gap between the forming and crashworthiness world.

The Challenge to Predict Material Failure in Crashworthiness Applications: Simulation of Producibility to Serviceability

In recent years, the requirements on passive safety of cars have grown to high standards, leading to a permanent demand on an increase in simulation accuracy. Additionally, demands on fuel efficiency and CO2 – reduction are confronting the car body designers with the need of substantial weight reduction. Here the increasing use of high and ultrahigh strength steel grades for bodies in white can be identified as major trend. At the same time simulation techniques are urged to predict formability and crashworthiness performance better and better. The present contribution will focus on one of the most urging challenges in sheet metal forming and crashworthiness simulation for high strength steels, namely alternative or enhanced constitutive formulations to predict failure and cracking of the blank and furthermore the inclusion of forming results in crashworthiness finite element models in order to predict material failure in such numerical investigations. In a broader view this simulation process chain may be termed as ’producibility to serviceability’ since the diving force behind forming simulations used to be the question if a certain part can be produced on certain press equipment with a defined number of forming stages from a specific material of given initial thickness. Carrying over the forming results to other simulation disciplines like crashworthiness or NVH, where the serviceability of the designed structure is investigated further, will eventually give more insight into the effects of pre-straining and possible pre-damaging emerging from production processes on the target discipline. The whole topic is rather demanding since nowadays the crashworthiness of bodies in white is assessed to a major extend by finite element simulations without taking the production history into account. In this context, high strength steel qualities are known to be more problematic. The present contribution discusses two possible engineering driven approaches to close the constitutive gap between the forming and crashworthiness world.