Edge cracking and stretch-flangeability evaluation
Optimised Hole Expansion Test (HET)
An optimised HET methodology has been developed through the investigation of the main parameters affecting the hole expansion ratio (HE) such as clearance, tool wear, burr position and time from punch to expand. An experimental test configuration has been developed to objectively measure crack initiation and propagation and obtain reliable and repetitive values of HER.
Half Specimen Dome Test (HSDT)
The Half Specimen Dome Test (HSDT) permits to determine the edge cracking behaviour of an open cut contour during sheet metal flanging. Compared to hole flanging tests, HSDT is a more time and cost-saving test for evaluating edge cracking. Another advantage is that is unaffected by aspects related to the tools manufacturing for cutting the holes, as the coaxiality between punch and die. The HSDT is combined with Digital Image Correlation (DIC) to obtain relevant edge fracture strain data for forming simulations.
Local damage evaluation of shear edges
Micromechanical techniques as nanoindentation tests and Electron Back-Scatter Diffraction (EBSD) allows to assess the local damage and properties of sheared areas. The extension of local damage in sheared areas can be evaluated measuring the Young’s modulus variation by a methodology developed using the nanoindentation technique. EBSD permits to evaluate the damage by the quantification of phase transformations, grain distributions and grain size variations, recrystallised grains and texture due to the cutting and forming processes.
