Comparative study of fracture criteria through bona fide experimental–numerical examinations on AA2024-T3

Lightweight aluminium alloys have been recognized as key actors in the aerospace industry due to their excellent strength-to-weight ratio. Appropriate formability estimators and deeper knowledge on the fracture behaviour would therefore benefit this preliminary production time. This paper aims to unprecedentedly complete comparative study of multiple promising fracture criteria on the 1.2-mm-thick AA2024-T3 sheet aluminium alloy through reliable practical forming processes to achieve the most faithful understanding of its fracture nature. Four fracture criteria–namely, Hill’48-R-MMC, Hill’48-S-MMC, Hill’48-R-Lou-Huh and Hill’48-S-Lou-Huh–in the form of fracture loci (FLs) are developed by means of numerical optimisation against the measured fracture strains at varying states. The strain data are extracted from the conventional fracture forming limit curve (FFLC), experimentally determined with the help of both standard Nakajima stretching and notched tensile tests. Two industrial forming parts like a classic square cup and an x-cross-shaped cup are employed to verify those four criteria. The criteria are put into service via the element-deletion feature in ABAQUS 2017, by which any element whose damage value reaches a certain limit is removed. In terms of final drawing depth, all four criteria produce satisfactory results; the best one from the Hill’48-R-Lou-Huh square cup has a slight error of 0.3%, whereas the two least acceptable ones from both Hill’48-S-based cross-die samples have an equal error of only 11%. In contrast, all Hill’48-S-based simulated cups have more matching crack appearances than Hill’48-R-based ones do.