Institute for Forming Technology and Forming Machines Research Aktuelle Projekte
Improved failure characterisation of high-strength steel sheet materials using a new test methodology for shear tensile tests in uniaxial tensile testing machines

Improved failure characterisation of high-strength steel sheet materials using a new test methodology for shear tensile tests in uniaxial tensile testing machines

E-Mail:  fem@ifum.uni-hannover.de
Year:  2019
Funding:  German Research Foundation (DFG)- Project number 405334714

Stress-based failure models offer advantages compared to conventional used forming limit curves (FLC). Non-linear strain paths in modern forming processes and various failure modes such as shear cracks and edge cracks, which occur when using higher strength steels, cannot be described using an FLC. However, to establish stress-based failure models in research and industry the following challenges must be dealt with:

  • Specimen failure due to crack initiation at free specimen edges
  • Insufficient resolution of process-relevant stress states
  • Inaccurate optical determination of the degree of failure deformation
  • A high variation of the stress state at the material point of crack initiation

To overcome these challenges this project aims to develop a new methodology for the determination of stress-based failure surfaces. The test method uses butterfly shear specimen and a test fixture that allows the variation of the force application angle to set different stress states in the range from shear to uniaxial tension in the specimen. In order to ensure a constant stress state, the force application angle is actively controlled and adjusted during the tests. The control is carried out by coupling the angle control with an optical measuring system as well as by supporting numerical simulations. The use of this new test methodology should increase the accuracy of damage modelling and thus of simulation-based design of sheet metal forming processes using high-strength steel sheet materials. In turn, this should enable better utilisation of the high potential of high-strength sheet steel materials for cost and weight reduction in automotive engineering.