3D cellular automata finite element modelling of cleavage and ductile fracture

In the present research work, a three-dimensional Cellular Automata Finite Element (CAFE) multi-scale model was developed to simulate, ductile fracture, cleavage and the ductile-brittle transition in a structural steel. For the simulation of the ductile-brittle fracture, at least two Cellular Automata arrays are needed, one to represent the ductile material properties and the other one to account for the brittle fracture process. The cell sizes in both arrays are independent of each other and of the finite element size. The cell sizes in each Cellular Automata array are related to the microstructural process of each fracture mechanism. The finite elements size is chosen to represent the macro strain gradients accurately. The model was implemented through the user define material behavior subroutine VUMAT in the finite element program ABAQUS Explicit Version 5.6. In the CAFE model, the material information is moved from the structural response of finite elements and stored in the appropriated number of Cellular Automata (CA) arrays. In the present CAFE model, the Rousselier ductile damage model was applied to each ductile cell. The critical value of the maximum principal stress was used to assess the failure of each brittle cell. In the brittle CA arrays, four different cleavage fracture nucleation micromechanisms, found experimentally at te.st temperatures down to -196øC in a ferritic-pearlitic Grade A ship plate steel were included in the model. This was done in order to simulate the real microfeatures nucleating cleavage in ferritic steels. In this model, the physical damage parameters of the ductile and brittle parts were calibrated separately. After calibration the CAFE model simulated the experimentally measured distribution of brittle microcracks generated in the notch region of blunt four point double-notch bend tests performed at test temperatures from 25øC to -196øC. The ductile part of the CAFE model was calibrated with the simulation of tensile and impact Charpy tests performed at room temperature. Subsequently the model was applied to simulate the ductile-brittle transition of Grade A ship plate steel. When numerical against experimental data was obtained, the parameters were considered true material model parameters of the steel under analysis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo