Abstract
Results of an experimental-numerical evaluation of a new butterfly specimen for fracture characterisation of AHHS sheets in a wide range of stress states are presented. The test on the new butterfly specimen is performed in a uniaxial tensile machine and provides sufficient data for calibration of common fracture models. In the first part, results of a numerical specimen evaluation are presented, which was performed with a material model of a dual-phase steel DP600 taken from literature with plastic flow and fracture descriptions. In the second part, results of an experimental-numerical specimen evaluation are shown, which was conducted on another dual-phase steel DP600, which was available with a description of plastic flow only and whose fracture behaviour was characterised in the frame of this work. The overall performance of the new butterfly specimen at different load cases with regard to characterisation of the fracture behaviour of AHSS was investigated. The dependency of the fracture strain on the stress triaxiality and Lode angle as well as space resolution is quantified. A parametrised CrachFEM ductile shear fracture model and modified Mohr-Coloumb ductile shear fracture model are presented as a result of this quantification. The test procedure and results analysis are believed to contribute to current discussions on requirements to AHSS fracture characterisation.
Highlights
Driven by high energy costs and stringent legal regulations on CO2 emissions during production and use of new vehicles, light-weight materials such as advanced high-strength steels with the ultimate tensile strength above 550 MPa (AHSS), aluminium and magnesium alloys as well as plastics are becoming extensively used in the automotive industry
This increases the safety of fracture initiation at a desired stress state as demonstrated in figure 6
The strain paths in figure 12 are deliberately shown for small and medium strains only as at higher strains the data determined with digital image correlation (DIC) went corrupt due to excessive shear deformation of the paint pattern applied to the surface
Summary
Driven by high energy costs and stringent legal regulations on CO2 emissions during production and use of new vehicles, light-weight materials such as advanced high-strength steels with the ultimate tensile strength above 550 MPa (AHSS), aluminium and magnesium alloys as well as (fibre-reinforced) plastics are becoming extensively used in the automotive industry. With the help of this numerical evaluation, spatial distribution of the equivalent plastic strain and damage variable in the specimen as well as time variation of the stress state at the location of fracture initiation were investigated.
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