Innovative toughness characterization for steel sheets and thin-walled structures

  Schlagzugversuch Copyright: IEHK Tensile impact test on 50J pendulum

The crack-arrest capacity of a material can be described by the impact toughness determined in the Charpy-V-notch test. In this case, a loading situation is provided which on the one hand is characterized by a notch in the specimen and on the other hand by the high impact speed of the hammer. The values determined in the Charpy-V-notch test can be used for the design of components in order to protect against a catastrophic failure of the material in a brittle fracture. However, the applicability of the Charpy-V-notch test is limited to larger sheet thicknesses since a standard sample must have a cross-section of 10 x 10 mm. Even smaller specimens with a cross-section of 3 x 4 mm cannot be used for sheet metals, which are frequently used in automotive engineering. For a long time this was not relevant for the component design, since a ductile failure of the material was to be expected in the range of conventional operating temperatures. Due to the development of multi-phase steels with complex microstructures, this cannot longer be assumed without any restrictions. The hard phases in these materials create an inhomogeneous stress state in the material, which can shift the tendency to failure into a brittle fracture in relevant temperature ranges. The project presented here therefore deals with the development of a tensile impact test, which can be used for the toughness characterization of thin sheets or thin-walled structures. With the help of a damage mechanics material model, a connection to the Charpy-V-notch test is possible so that the new test technology also provides values for the use in current design standards. Furthermore, a sample catalogue should be developed, which enables a selective check of individual stress states. This catalogue allows the user to meet the requirements of the material toughness, which can then be tested in a fast process.