Improved Fracture Characterization of High Strength Steels due to a new Test Method for Shear Tension Specimen on uniaxial Tensile Testing Machines

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In order to maintain the dominating position of advanced high-strength steels (AHSS) as compared to other lightweight materials in automotive industry, there is a need for continuous development of AHSS as well as a better utilization of their lightweight potential. The numerical analysis of forming processes on basis of FEM provides an effective method to improve this utilization.In contrast to the conventional method for the description of fracture strains in sheet metal forming processes with the help of FLD, stress-based fracture models can be used for forming processes with non-linear strain paths as well as multi-stage forming processes, and furthermore, besides ductile fracture also shear fracture can be predicted. The calibration of stress-based fracture models has not been standardized yet. Therefore, estimated fracture strains of AHSS available in literature often differ much from one author to another because of different testing procedures with varying developments of the stress state in the fracture initiation zone of the specimen. The objective of the project is to develop a procedure for uniaxial tensile testing machines based on shear tension tests, whereby it is possible to calibrate precisely the fracture behaviour of AHSS for a wide range of stress-states. For this purpose, an already developed butterfly specimen will be used and a new test device will be developed. This device will allow adjusting continuously the angle between the specimen and the force direction of the testing machine during the test thus a constant stress state in the specimen can be maintained.