Crack tip plasticity in plastically graded Ni-W electrodeposited nanocrystalline alloys

In the present paper, it is analyzed the problem of a crack approaching a plastically graded microstructure along its path. The problem regards a nanocrystalline electrodeposited material in which the plastic properties (yield stress, hardness, UTS) vary much more than the elastic ones (Young modulus and Poisson ratio). In the present paper, the analysis has been conducted by employing ABAQUS simulations on nanocrystalline Ni-W alloys with 20 and 100 nm constant grain size; the results were compared with those of the plastically graded sheets with negative graded configuration in which the grain size varies between 20 and 100 nm from the surface to the bottom in a linear way and with positive graded configuration in which the grain size varies between 100 and 20 nm from the surface to the bottom in a linear way. The finite element study has conducted to the conclusion that the grade in the microstructure and consequent plastic mechanical properties of nanocrystalline Ni-W alloys leads to several changes in the driving force for fracture demonstrated by the different behavior of the effective J-integral at the crack tip in the different studied configurations. (C) 2007 Elsevier B.V. All rights reserved.