Determination and modling of dynamic material characteristics for FE crash simulations

• Applicants: Professor Dr.-Ing. Xiangfan Fang; Professor Dr.-Ing. Sebastian Münstermann
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391544620

Large deformations with high strain rate range of 1000 1/s occur during a real vehicle crash, which must be correctly described for the FE-simulation of vehicle development. The experimental determination of the material characteristic has been carried out by using three different techniques due to the system ringing effect of the test installations. The material data for FEM are partially inaccurate and incomplete. Some material parameters must be calculated by using a reverse engineering method. This approach is non-physical. During the pre-works of the applicant, a new specimen geometry has been developed with which a force measurement, without any system ringing can be realized. Additional material parameters can also be measured.In phase 1 of this project the physics behind the new ringing free force measurement have been understood by using a 1-dim. wave model and based on dislocation damping. The principles were then applied on five different notched specimens, with which different stress triaxialities were realized. The yield and the fracture locus were exactly measured at speed of up to 10m/s which is far beyond the state of the art. It can be observed that the expansion of the yield and fracture locus as a function of strain is non-uniform and depends on the stress state and the strain rate. The undesired strong increase of the strain rate after the specimen necking has also been solved for quasi-static tests completely. For dynamic tests, the most promising concepts are still being investigated. After almost all of the planed goals in phase 1, which were proved by DFG, have been successfully met, the project should be continued in the phase 2. This project continuation application follows the statement of DFG that one additional project partner of material science should be involved. In this way, in addition to the improved description of plasticity and damage of the investigated steels as well as the macroscopic material modelling, further knowledge about the microscopic influences on plasticity, damage and fracture should be gathered. This should be done by using a multi-scaled modelling concept.At first, the non-uniform expansion of the yield surface in stress space should be modelled and implemented into the continuum mechanical (CM) damage models. To carry out the multi-scaled modelling, 3D-SRVEs will be built in which the constitutive material behaviours will be described by CP-models. In this way, the material mechanisms during the crash event can be modelled and understood. In addition, the non-measureable “damage initiation” parameter for the CM-models should be also calculated by 3D-SRVEs. The “reverse engineering” is then not needed anymore. At the end of the project a method will be developed which enables a quantitative relationship between microstructure, dynamic properties of the materials and the crash behaviors of car component.

• DFG Programme: Research Grants