Prediction of the blanked edge using only a tensile test
Citation for published version (APA):Goijaerts, A., Govaert, L. E., & Baaijens, F. P. T. (1999). Prediction of the blanked edge using only a tensile test. Poster session presented at Mate Poster Award 1999 : 4th Annual Poster Contest.
Document status and date: Published: 01/01/1999 Document Version:
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Prediction of the blanked edge using only a tensile test
A.M. Goijaerts, L.E. Govaert and F.P.T. Baaijens
Eindhoven University of Technology, Faculty of Mechanical Engineering,
Section Materials Technology,
P.O. Box 513, 5600 MB Eindhoven, the Netherlands
Introduction
The shape of the blanked edge can be very important for the functionality of a blanked product. Up till now it has not been possible to predict this shape, resulting in trial and error in the design of blanking processes. Critical issue is the prediction of ductile fracture initi-ation, which determines the aforementioned shape:
6 Blankholder Punch Sheet Die Blank Burr Fracture zone Shear zone Roll−over Clearance
Objective
To ensure wide applicability, easily accessible exper-imental tools are desired. Therefore, we aim at the prediction of the shape of the blanked edge using only tensile tests for the quantification of ductile fracture.
Ductile fracture initiation
Existing fracture criteria do not suffice. A new crite-rion is postulated, valid for both blanking and tensile testing under different pressures [1]:
¯εp
< 1 + 3.9 · σh/ ¯σ > ¯ε0p.63d¯εp= C (1)
with ¯εp the equivalent plastic strain andσh/ ¯σ the
hy-drostatic stress divided by the equivalent stress (tri-axiality). When the integral reaches the material pa-rameter C, ductile fracture initiates. This C can be de-termined using a tensile test and its FEM-simulation:
εp Views perpendicular to fractured neck: 0.00 0.25 0.50 0.75 1.00 1.25
The C is equal to the simulated value of the integral expression at the moment and at the location of duc-tile fracture initiation (considering the fractured neck).
Prediction of the blanked edge
As the C is determined in a tensile test, ductile frac-ture initiation can be predicted in the blanking process for different geometries using some advanced FEM-tools [2]. Predictions (left, colors depict the level of the integral expression of equation 1) are confronted withexperiments(right):
Prediction 0 1 3 6 10 15 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Clearance [% of thickness] P unch d is pl . a t fracture (a+ b+ c) [m m ]
Small cutting radii of tools
Large cutting radii of tools a
b
c
Experiment
Results for 4 materials
For every material one tensile test is performed to de-termine the C. Predictions are confronted with exper-iments: 1 3 6 10 15 0 0.2 0.4 0.6 0.8 1
Stainless steel (ferr.) Stainless steel (aust.) Deepdrawing steel Aluminum Clearance [% of thickness] P unch d isplacem ent at fr act u re [m m ]
Predictions for two materials are within or close to the experiments. Two other materials have maximum de-viations in the order of 10-15%.
Conclusion
We can predict the shape of a blanked edge for differ-ent blanking geometries for differdiffer-ent materials using only a tensile test.
References:
[1] A.M. GOIJAERTS:Prediction of ductile fracture in metal blanking, Ph.D. thesis, Eindhoven University of Technology, 1999 [2] D. BROKKEN:Numerical modelling of ductile fracture in blanking, Ph.D. thesis, Eindhoven University of Technology, 1999
