The instrumented 3-point bending test according to VDA238-100 test standard is increasingly used within the steel and automotive industry. Originally developed for aluminum hemming characterization, this bending test has been shown to be also relevant for local formability and crash foldability assessment originally of press-hardened steel grades and more recently for newly developed advanced and ultra high strength AHSS/UHSS steels grades. This instrumented bending test delivers bending load vs. bending angle curves. It is commonly assumed that material failure shortly happens beyond maximum load after a 30N load drop. The bending angle at maximum force aFmax characterizes then the bendability of the investigated material. The assumption maximum force = bending crack initiation, while being true for press-hardened grades, is in too many case not valid for steel grades with tensile strength ⩽1200MPa and cannot be universally trusted. An alternative approach is presented using passive acoustic emission sensors placed in the vicinity of the bending punch. The interpretation of such acoustic data is however quite subjective and still in trial status. Redundant crack detection systems based on load, acoustic as well as optical measurements may have to be considered together for increasing crack detection reliability within the VDA238-100 bending test specification.

Shear cutting introduces residual strains, notches and cracks, which negatively affects edge-formability. This is especially relevant for forming of high-strength sheets, where edge-cracking is a serious industrial problem. Numerical modelling of the shear cutting process can aid the understanding of the sheared edge damage and help preventing edge-cracking. However, modelling of the shear cutting process requires robust and accurate numerical tools that handle plasticity, large deformation and ductile failure. The use of conventional finite element methods (FEM) may give rise to distorted elements or loss of accuracy during re-meshing schemes, while mesh-free methods have tendencies of tensile instability or excessive computational cost. In this article, the authors propose the particle finite element method (PFEM) for modelling the shear cutting process of high-strength steel sheets, acquiring high accuracy results and overcoming the stated challenges associated with FEM. The article describe the implementation of a mixed axisymmetric formulation, with the novelty of adding a ductile damage- and failure model to account for material fracture in the shear-cutting process. The PFEM shear-cutting model was validated against experiments using varying process parameters to ensure the predictive capacity of the model. Likewise, a thorough sensitivity analysis of the numerical implementation was conducted. The results show that the PFEM model is able to predict the process forces and cut edge shapes over a wide range of cutting clearances, while efficiently handling the numerical challenges involved with large material deformation. It is thus concluded that the PFEM implementation is an accurate predictive tool for sheared edge damage assessment.

There is a growing interest in correlating usual tensile testing results with edge crack sensitivity testing from punched ISO16630 hole expansion ratio HER (10mm shear cut hole, 12% clearance, conical expansion tool). A new kind of tensile local ductility parameter has been developed lately based on broken sample surface of tensile specimens after testing. Reduction in area or thickness at fracture are more sensitive than conventional fracture elongation with a 50 to 80m gage length to characterize the local ductility potential of sheet steels. A representative amount (300 different sets of samples) of cold rolled sheet steels have been tested in the tensile strength range 600-1200MPa and thickness range 1-2mm with 3 replicates in the transverse and longitudinal direction with ISO 6892-1, type 2, A₈₀ tensile samples. Correlation levels of ISO16630 HER values with conventional tensile mechanical properties such as uniform & fracture elongation, yield & tensile strength, n-& r-values or derivatives are disappointing low for the investigated AHSS grades. There is however a massive improvement in the empirical statistical correlation when using local ductility properties based on fracture area or thickness reduction measurements on broken tensile samples. Logarithmic local ductility strains correlate generally linearly with logarithmic hole expansion ratio. Logarithmic true local ductility values are proving more suitable than engineering strains for correlations. Transverse direction improves slightly the correlation quality vs. longitudinal direction. The correlation is also higher for thickness reduction in comparison to reduction of area based properties.