Single point incremental forming of AA6061 thin sheet: calibration of ductile fracture models incorporating anisotropy and post forming analyses

Nowadays, single point incremental forming (SPIF) process is gaining popularity for fabrication of various asymmetrical intricate sheet metal components in automobile, aerospace, ship-building, additive manufacturing and also in biomedical sectors. In the present work, a SPIF set up was designed and developed in-house to perform forming experiments using AA6061 thin sheet material. The fracture forming limit diagram (FFLD) was assessed experimentally using punch stretching test, and it was validated with the optimized SPIF test data. Further, an effort was made to modify the existing seven damage models implementing Hill48 anisotropy plasticity theory. Consequently, the effective plastic strains at the onset of fracture were predicted and compared with experimental data. All the critical damage parameters of investigated ductile fracture models were successfully calibrated using uniaxial tensile test data, and the theoretical FFLD was also estimated incorporating the anisotropy plasticity theory. Among the seven damage models, the Bao-Wierzbicki (BW) damage model was found to be the most efficient damage model with an average absolute error of 2.71%. Additionally, the influence of sheet metal anisotropy on the effective fracture strain was studied by comparing the fracture strain in 2D (η, LP) and 3D (η,LP,ε¯f\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \eta, {L}_P,{\overline{\varepsilon}}_f $$\end{document}) fracture locus. In order to get insight into forming behaviour and surface roughness, the microstructural examination on the truncated dome fabricated using optimised parameters was carried out through micro texture analyses.