Micromechanics-based modified ductile fracture criterion for extruded aluminum alloys under multi-axial loading

Abstract

Aluminum alloys are increasingly finding applications in various construction projects, particularly in significant public buildings, and their ductile fracture under extreme situations is worth noting. While many ductile fracture criteria have been developed for metals, their applicability to structural aluminum alloys has not been systematically investigated. This paper focuses on the ductile fracture criteria of aluminum alloys over a wide range of stress states. Experimental studies were conducted to demonstrate the significant effect of stress states on the fracture ductility of aluminum alloys (6061-T6, 6082-T6, and 6063-T5). Through a finite element unit cell-based micromechanics analysis, the influence laws of stress triaxiality and Lode angle on ductile fracture are elucidated, and a modified fracture criterion (Modified Johnson-Bai) is proposed. Subsequently, the prediction accuracy of two classical fracture criteria and the modified criterion is systematically discussed. The modified fracture criterion exhibits the highest accuracy with an acceptable number of fracture parameters to be calibrated, indicating its sufficient flexibility and operability in fracture prediction of structural aluminum alloys. Finally, a parameter calibration procedure applicable to commonly used thin-walled members was established and validated by a group of newly designed specimens, providing a reliable framework for predicting fracture in structural applications involving aluminum alloys.