Failure Analysis With a New Tool Geometry, X-Die, in Areas With High Tension/Compression Strains

• Sheet-metal forming involves a complex strain distribution over the part. The strains consist of tension, compression, and a mix of both. A geometry has been developed, the X-Die, in order to gain insight into the strain behavior of different materials. The X-Die enables strain paths far into the tension/compression region, thus creating the possibility to extend the experimental base both for definition and for further extrapolation of the Forming Limit Curve (FLC) in the tension/compression region, as well as to evaluate FE-simulation results for the same region.Today, evaluation of cracks is made by using FLC. In the conventional test methods, the strains only reach 40% compression (true strain) and often much lower percentages. In conventional test methods, the FLC for any region beyond these levels is extrapolated from existing data.The experimental test proposed in this work consists of a geometry, the X-die, which has shown that rates of 70% tension/compression can be reached (point 0.7/−0.7 in the FLC). Thereby, the region for prediction of cracks on the compression side can be extended in the Forming Limit Diagram (FLD). Furthermore, the strain paths are easy to follow and the limits when cracks appear can be evaluated. Furthermore, the experimental results show that the behavior depends on the material quality. Qualities such as Extreme High Strength Steel (EHSS) and Aluminum have a limited tension/compression rate due to failure in plane strain tension. Material qualities with high r-values, e.g. Mild steel and High Strength Steel (HSS), reach high tension/compression rates before failure and have regions with clearly defined strain signatures. This will be favorable for comparison with numerical simulations, especially for strain signatures in the tension/compression region. Furthermore, the experiments did not indicate any limitation in the compression region besides the one defined in the normal procedure in creation of an FLC.This geometry is favorable to calibrate simulation results, in order to analyze prediction of strains located on the left side in an FLD. ©2007 American Institute of Physics

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TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

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