1 Introduction and motivation
- When designing formed components, light weighting potential is not fully exploited because damage cannot be taken into account and higher safety factors have to be used instead.
- When designing the forming process itself, not all influencing factors on the performance of the component are taken into account.
2 Vision and scope
- Research of damage-controlled forming processes In order to be able to specifically adjust the damage during forming, it is necessary to understand how the load paths (strain path, temperature, triaxiality, load angle, etc.) can be influenced in the individual forming processes and how these load paths interact with the metal-physical damage mechanisms. An important aspect is to survey methods of controlling the damage level in classical forming processes and hence increase the performance of the components. First applications of this approach for sheet forming and bulk forming are presented in [9].
- Research of measuring techniques for the quantitative detection of damage In order to develop a model description of damage, the metal-physical damage mechanisms located on different length scales must be precisely resolved. In order to describe the damage initiation phase in multi-phase steels in particular, high-resolution characterization methods, such as in-situ testing technology in scanning electron microscopy, must be developed further. While ductile damage is usually the dominant mechanism during forming, the performance of a component in many cases also depends on its cyclic strength. Here it is to be expected that pores caused by ductile damage influence in particular the incubation and short crack growth phases during subsequent cyclic loading. For this reason, the fundamental question must be answered which experimental methods can characterize, quantify and separate the interaction of ductile and cyclic damage mechanisms. A recent comparison of several methods to determine the damage value [4] concludes that different methods can yield quantitatively different results where some additionally exhibit large margins of uncertainty.
- Modelling and prediction of the initiation and development of damage Although the modelling of damage is not fundamentally new and a large number of different, partly empirical models are known in literature, their validation is usually only based on a specific application, so that the knowledge gained cannot be generalized. Accordingly, the fundamental questions as to which different mechanisms govern the different forming processes and how these mechanisms are influenced by common process parameters are still largely unknown. Similarly, the possibilities for healing damage and the effect of damage on component performance are not yet fully understood. These deficits are due to the intrinsic multi-scale nature of the damage: Damage on the macroscopic scale (e.g. a crack) depends on damage on the microscale (e.g. initiation and development of microcracks and micropores). Furthermore, in contrast to other multi-scale problems in modeling, damage is usually associated with material softening. This firstly results in the necessity of regularization as highlighted before [3] and secondly in the fact that damage can merely be described by classical homogenization methods so that further research is required.