3D CAFE modelling of transitional ductile fracture in steels

A coupled Cellular Automata - Finite Element (CAFE) three-dimensional multiscale model was applied in this work to the simulation of transitional ductile brittle
fracture in steels. In this model material behaviour is separated from the representation of structural response and material data is stored in an appropriate number of cellular automata (CA). Two CA arrays, the "ductile" and the "brittle", are created, one is to represent material ductile properties, another is to account for the brittle fracture. The cell sizes in both arrays are independent
of each ot her and of the finite element (FE) size. The latter is chosen only to represent accurately the macro strain gradients. The cell sizes in each CA array
are linked to a microstructural feature relevant to each of the two fracture mechanisms. Such structure of the CAFE model results in a dramatic decrease of the
!lumber of finite elements required to simulated the damage zone. Accordingly the running times are cut down significantly compared with the conventional FE
modelling of fracture for similar representation of microstructure. The Rousselir continuing damage model was applied to each cell in the ductile CA array.
The critical value of the maximum principal stress was used to assess the failure of each cell in the brittle CA array. The model was implemented through auser material subroutine for the Abaqus finite element code. Several examples of model performance are given. Among them are the results of the modelling of the Charpy test at transitional temperatures. For a laboratory rolled TMCR
steel the model was able to predict the transitional curve in terms of the Charpy energy and the percentage of brittle phase, including realistic levels of scatter, and the appearance of the Charpy fracture surface. The ways in which material data can be fitted into the model are discussed and particular attention is drawn upon the significance of the fracture stress distribution.