Evolution of voids during ductile crack propagation in an aluminium alloy sheet toughness test studied by synchrotron radiation computed tomography

The anisotropy of fracture toughness in AA2139 (Al-Cu-Mg) alloy sheet has been investigated via synchrotron radiation computed tomography of arrested cracks in Kahn tear test pieces for different loading cases. The three-dimensional distribution and morphology of pores and defects in the as-received state are seen to be anisotropic, with chains of voids and void elongation in the L (longitudinal) direction. For toughness testing in L-T orientation (T is long transverse), voids ahead of the crack grow and link in the L direction. In T-L tests, voids ahead of the crack tip also grow in the loading direction, although a high degree of alignment is retained in the L direction. The present work provides quantitative microstructural data that can be used as input for and validation of recent idealized model formulations, and it is shown that the measured void dimensions and evolution are consistent with measured toughness anisotropy. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.