Physical modeling of intermittent plasticity during indentation-induced deformation in BCC metals

Pop-in phenomenon that corresponds presumably to local plasticity initiation or subsequent plastic deformation was detected on load-displacement curves with major parameters of critical load Pc and corresponding excursion depth Δh. Since the maximum shear stress underneath the indenter upon plasticity initiation is estimated in an order of a theoretical strength, the event can be understood as dislocation nucleation from defect-free region in a crystal. A probability of Pc for thousand measurements on [001] oriented bcc single crystal Fe shows Gaussian distribution, suggesting a thermally-activated process as an elementally step of the event. On the other hand, the second or later event indicates power-law function like Gutenberg-Richter model, which presumes a collective avalanche-like motion of preexisting dislocations.