Framework for adjusting for both stress triaxiality and mesh size effect for failure of metals in shell structures

The current paper provides a procedure for adjusting the failure strain of shell elements based on both mesh size and stress triaxiality. This procedure is a general framework that gives a homogenisation of a neck over the entire length of an element and it uses an arbitrary forming limit diagram (FLD) and stress triaxiality-based failure criterion as input. In the example given in this paper, a Swift FLD is used together with the plane stress version of the modified Mohr-Coulomb failure locus. The results of this study show that simply scaling a failure locus is not correct. The proposed method produces the same mesh size correction for uniaxial tension as prior studies, but it produces different levels for other states of stress. In the limit of very large element sizes, it degenerates to the FLD.