Intergranular fracture prediction via multi-scale simulations
Abstract
Observations of intergranular fracture initiation during slow strain rate tests highlight two relevant mechanisms occuring at grain boundaries (GB): stress concentrations induced by the impact of slip bands and selective internal oxidation in water environment. The pile-up theory modeling a slip band as a slip plane of negligible thickness in a continuum elastic medium is generaly used with the Griffith criterion. However this approach leads to large underestimation of the remote stress to GB fracture. Slip band of finite thickness (20-200 nm) inducing more realistic singularities are investigated by using crystalline finite element calculations. A new approach using quantized fracture mechanics in conjunction with a double criterion permits to deduce a model of intergranular crack initiation. This multi-scale analytical model is used with molecular dynamics results of oxide grain boundaries decohesions for assessing the oxidation embrittlement of the interface. An extensive application of the model is carried out for numerous materials. Predictions are in good agreement with experimental results.