Fracture mechanisms under monotonic and non-monotonic low Lode angle loading

• Monotonic and non-monotonic low Lode angle experiments.
• Effect of pre-strain at low stress triaxiality on ductile fracture.
• Negative stress triaxiality cut-off value for fracture under low Lode angle loading.
• Analysis of double curvature specimens and punching tests.

Ductility of high-strength low-alloy steel S420MC was investigated by means of experiments and finite element analyses. Monotonic and non-monotonic low Lode angle experiments were carried out using double curvature specimens and punching tests. Punching tests allow investigating material behavior under zero Lode angle and from low to high stress triaxiality ratios. Investigated material exhibits significant increase of ductility with stress triaxiality decrease. Under low enough stress triaxiality, loss of load carrying capacity and fracture were not observed. Even if fracture is not observed under these conditions, pre-strains under very low stress triaxiality induce relative loss of ductility when the material is loaded again at higher stress triaxiality.