Effect of grain disorientation on early fatigue crack propagation in
face-centred-cubic polycristals: A three-dimensional dislocation dynamics
investigation
Three-dimensional dislocation dynamics simulations are used to study
micro-crack interaction with the first micro-structural barrier in face-centred
cubic bi-crystals loaded in high cycle fatigue conditions. In the examined
configuration, we assumed that micro-crack transmission occurs due to surface
relief growth in the secondary grain ahead of the primary crack. This indirect
transmission mechanism is shown to strongly depend on grain-1/grain-2
disorientation. For instance, small grain disorientation induces plastic strain
localisation ahead of the crack and faster transmission through the first
barrier. Conversely, large grain-1/grain-2 disorientation induces plastic
strain spreading similar to crack tip blunting yielding slower indirect
transmission. A semi-analytical micro-model is developed based on the present
simulation results and complementary experimental observations highlighting the
original notion of first-barrier compliance. The model captures well known
experimental trends including effects of: grain-size, grain disorientation and
micro-crack retardation at the first barrier
