Near-tip closure and cyclic plasticity in Ni-based single crystals

Fatigue crack growth was investigated in a 001 oriented single crystal specimen, made of a Ni-based superalloy, Haynes 230. Crack propagation was characterized with digital image correlation: crack closure, measured by analyzing the relative displacements of crack flanks, showed closure levels much lower than polycrystal alloys. Reversed plastic zones were calculated from regressed stress intensity factor ranges and compared to the strain field measured at the crack tip. Experimental results were compared to those provided by a numerical model, which considered both crack propagation and single crystal anisotropic behavior, in terms of crack opening levels and crack tip cyclic plastic zones. Results of the numerical simulations were in good agreement with the experiments.