P-1268P-1268

P 1268 – Characterization and crash modelling of notch effects through mixed joints in components made of high strength steels

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P 1268 – Characterization and crash modelling of notch effects through mixed joints in components made of high strength steels

The necessity to reduce the fuel consumption of modern vehicles requires the reduction of the car body mass. In particular, the multi-material construction shows considerable potential for weight savings with a high level of passive safety at the same time. The combination of press-hardened steel with aluminum is therefore widely used in the development of modern car bodies. It has to be minded that the multi-material construction poses particular challenges for the joining technology, since different types of materials cannot be welded easily. Therefore, alternative joining techniques such as the selfpiercing riveting or the resistance and friction element welding are used more often.
These joints are always technical notches within the component, whereby the type of notch effect can be differentiated based on the used joining process. Mechanical joining techniques result in a geometrical notch due to the punched hole, with high plastic strains at the edge of the hole. Thermo-mechanical joining techniques result in a metallurgical notch due to the heat-affected zone, which develops during the joining process due to the induced heat.
In this research project, the influence of different notch effects due to various joining techniques (self-piercing riveting, semi tubular self-piercing riveting, resistance element welding, friction element welding) on the load bearing capacity of component structures is investigated experimentally and numerically. Therefore, tests under quasi-static and dynamic load were conducted with specimens, which have been notched due to the investigated joining techniques. Furthermore, LWF-KS-2-tests have been performed under quasi-static and dynamic load in order to characterize the load bearing  capacity of the investigated joining techniques under various different loading angles. Finally, the on specimen level observed findings where validated based on component tests, which have been conducted under quasi-static and dynamic load.
Based on the experimental results of the notched specimen tests substitute models have been developed, which are able to detect specimen failure due to notch effects under in-plane load. Additionally *CONSTRAINED_SPR3 (model 2) substitute model parameters have been determined based on the results of the LWF-KS-2-tests in order to represent the load bearing capacity of the joint itself within the simulation. The calibrated models have been validated for more complex load cases based on the experimental results of the component test. Based on the results of this research project, users of the investigated joining techniques are able to estimate the influence of the induced notch effects on the load bearing behaviour of component structures. With the help of the developed modelling strategies for the notch-related component failure in the substitute modeling of joints, this failure case can be taken into account early in component development.

Published in:
2021

Authors:
Prof. Dr. rer. nat. P. Gumbsch, Prof. Dr.-Ing. G. Meschut