Characterization of fracture loci in metal forming

•New analytical framework to characterize fracture loci in metal forming under plane stress conditions.•Characterization of fracture loci in metal forming in the light of crack separation modes I, II and III.•Independent treatment of surface cracks for sheet and bulk metal forming processes.•Representation of fracture loci in the principal strain space and in the space of the effective strain at fracture vs. stress triaxiality.

Fracture in metal forming can occur in three different modes: (i) tensile; (ii) in-plane shear; and (iii) out-of-plane shear (respectively the same as modes I, II and III of fracture mechanics). The circumstances under which each mode will occur are identified in terms of plastic flow and microstructural ductile damage by means of an analytical framework to characterize fracture loci under plane stress conditions that also takes anisotropy into consideration.Experimental results retrieved from the literature give support to the presentation and show that plastic flow and failure in sheet forming results from competition between modes I and II whereas in bulk forming fracture results from competition between modes I and III.