Experimental and numerical analysis of toughness anisotropy in AA2139 Al-alloy sheet

Toughness anisotropy of AA2139 (Al–Cu–Mg) in T351 and T8 conditions has been studied via mechanical testing of smooth and notched specimens of different geometries, loaded in the rolling direction (L) or in the transverse direction (T). Fracture mechanisms were investigated via scanning electron microscopy and synchrotron radiation computed tomography. Contributions to failure anisotropy are identified as: (i) anisotropic initial void shape and growth; (ii) plastic behaviour including isotropic/kinematic hardening and plastic anisotropy; and (iii) nucleation at a second population of second-phase particles leading to coalescence via narrow crack regions. A model based in part on the Gurson–Tvergaard–Needleman approach is constructed to describe and predict deformation behaviour, crack propagation and, in particular, toughness anisotropy. Model parameters are fitted using microstructural data and data on deformation and crack propagation for a range of small test samples. Its transferability has been shown by simulating tests of large M(T) samples.