Taylor-based nonlocal theory of plasticity: numerical studies of the micro-indentation experiments and crack tip fields

Recent advances in strain gradient plasticity have provided a means to quan titatively characterize the experimentally observed size effect at the micr on and submicron scales. The introduction of strain gradients in the consti tutive model has increased the order of governing equations and therefore r equire additional boundary conditions in some theories of strain gradient p lasticity. Is it possible to develop a micro-scale plasticity theory that p reserves the structure of classical plasticity? The Taylor-based nonlocal t heory (TNT) of plasticity (Int. J. Solids Struct. 38 (2001), 2615) was deve loped from the Taylor dislocation model for this purpose. We have proposed a finite element method for TNT plasticity, and have applied it to study mi cro-indentation experiments. The micro-indentation hardness predicted by TN T plasticity agrees very well with the indentation hardness data. We have a lso studied the crack tip field in TNT plasticity, and have found that the stress level in TNT plasticity is significantly higher than that in classic al plasticity. This provides an alternative mechanism for cleavage fracture in ductile materials observed in Elssner et al.'s experiments (Scripta Met all. Mater. 31 (1994) 1037). (C) 2001 Elsevier Science Ltd. All rights rese rved.