Microstructural modelling of creep crack growth from a blunted crack

The effect of crack tip blunting on the initial stages of creep crack growt h is investigated by means of a planar microstructural model in which grain s are represented discretely. The actual linking-up process of discrete mic rocracks with the macroscopic crack is simulated, with full account of the underlying physical mechanisms such as the nucleation, growth and coalescen ce of grain boundary cavities accompanied by grain boundary sliding. Result s are presented for C*-controlled mode I crack growth under small-scale dam age conditions. Particular attention is focused on creep constrained vs. un constrained growth. Also the effect of grain boundary shear stresses on lin king-up is investigated through shear-modified nucleation and growth models . The computations show a general trend that while an initially sharp crack tends to propagate away from the original crack plane, crack tip blunting reduces the crack growth direction. Under unconstrained conditions this can be partly rationalized by the strain rate and facet stress distribution co rresponding to steady-state creep.