Anisotropy in fracture behavior of thin Al 7075-T651 plates

The objective of this study was to relate, if possible, the anisotropy in fracture resistance with the anisotropy in elastic properties of thin (6.38 mm) plates of aluminum alloy 7075-T651. Fracture resistances, as characterized by fracture toughness K-Q associated with the plane-stress condition, were measured in L-T, L + 30, L + 60 and T-L orientations. These tests revealed a significant anisotropy in K-Q values with the K-Q in the T-L orientation being 20.6% smaller than K-Q in the L-T orientation. Tension tests revealed anisotropy in the elastic properties (elastic modulus and Poisson's ratio) too, with the Poisson ratio in the longitudinal direction being 2.68% larger than in the transverse direction. The Strain-Energy-Density (SED) and the Maximum=Tangential-Stress (MTS) criteria were used to correlate the anisotropy in elastic properties with fracture resistance. Calculations, based on the SED and MTS criteria, showed that the anisotropy in elastic properties was inadequate to explain the large anisotropy in K-Q values. Copyright (C) 1996 Elsevier Science Ltd