Investigation of size effects on the plastic zone properties at crack tipWednesday (26.09.2018) 17:45 - 18:00 S1/01 - A4 Part of:
The erratic behaviour of short cracks propagation under low cyclic loading in ductile metals is commonly attributed to a complex interplay between stabilisation mechanisms that occurs at the mesoscopic scale.
Among these mechanisms, the interaction with the existing dislocation microstructure play a major role. The dislocation microstructure is source of plastic deformation and heat transfer that reduce the specimen stored elastic energy, screen the crack field due to its self-generated stress field or change the crack geometry through blunting mechanisms. In this study, these mechanisms are investigated with 3D-DD simulations using the Discrete-Continuous Model, modelling three different crack orientations under monotonic traction loading, promoting mode I crack opening.
Surprisingly, screening and blunting effects do not seem to have a key role on mode I crack stabilisation. Rather, the capability of the specimen to deform plastically without strong forest hardening is found to be the leading mechanism. Additional investigations of two different size effects (plastic zone confined introducing grain boundaries around the crack tip and reduction of the physical size of the system) confirm those results and show the minor contribution of a polarised dislocations density and the associated kinematic hardening on crack stabilisation