Multiscale investigation of ductile fracture mechanisms and strain localization under shear loading in 2024-T351 aluminum alloy and 36NiCrMo16 steel

Ductile fracture mechanisms under shear loading have been investigated in 2024-T351 aluminum alloy and 36NiCrMo16 steel through interrupted torsion tests followed by SEM observations and through direct monitoring of damage during in situ torsion tests in a SEM. Strain localization was observed at meso-scale, but also at micro- and sub-grain scale. A significant axial elongation was measured in both materials during the torsion tests. This “Swift effect” might partly explain why in the aluminum alloy most voids elongate in one direction and shrink in the orthogonal one but do not completely collapse and why some voids even grow. The crystallographic texture and its evolutions - quite significant in the ductile 36NiCrMo16 steel - play a significant role. No void nucleation was observed in steel. Microcracks initiated at an early stage but did not grow up to a large shear strain. Due to some reorientations, clusters of grains sharing the same orientation appeared. This favored shear bands development and microcracks growth.