A Weibull perspective on the fracture of atom probe specimens.

Poster presented at M&M 2013.

Little is known and understood of the fundamental mechanisms underpinning the fracture of atom probe specimens during their analysis. Yet it is one of the main experimental limiting factors, as most experiments end with the specimen’s fracture. The stress associated with the electric field (electrostatic pressure) has been estimated via various methods and is known to be very intense, in particular towards the specimen apex, where the electric field is enhanced by the lightning rod effect. Observation of elastic deformation as well as stress-induced twinning have both been reported.

The investigation by Moy et al. made use of finite-element simulations to derive the stress distribution along the specimen, and demonstrated a strong dependence on the specimen geometry. Interestingly, the fracture is known to occur somewhere down the shank of the specimen and not where the normal stress is the most intense, at the specimen apex. For a long time, this was only poorly understood. Here we propose that the Weibull theory (i.e. theory of weakest link) of brittle fracture can be applied to the fracture of atom probe specimens.