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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
Research Student Awards

PhD Thesis: Coupled finite element and cellular automata simulations of plastic flow and microstructural evolution

Author: QIAN, Ming

Year: 2007

Supervisor(s): Xiao Guo

The focus of the project is to establish a modelling approach that couples Cellular Automata (CA) and Finite Element (FE) methods to simulate microstructural variation due to concurrent deformation and recrystallization. Firstly, a 2D CA model for Dynamic Recrystallisation (DRX) was designed and validated by experiment. The bridging methodology and computational code were developed to enable smooth data transfer between the CA and the FE (CAFE) to simulate morphology of microstructure and its effect on macroscopic flow behaviours. The CAFE code transfers the data after each certain incremental time step to imitate simultaneous plastic deformation and microstructural evolution. The CAFE code was applied to two initialised microstructures for a two-phase alloy (Ti6A14V) using different plastic deformation models in FE. The first was carried out, using a conventional static elasto-plastic FE module, where effective plastic strain was transferred as a scalar in CAFE. The second improved the initial microstructures and deformation model by means of a set of strain rate dependent equations based on a quasi-static module. The key parameters transferred in the CAFE were the recrystallised strain tensor, the effective stress and the critical strain. The stress-strain curves in relation to microstructure evolution were successfully simulated. The actual nucleation rate was also simulated under different deformation conditions using a linear probability nucleation criterion. A time dependent expression for nucleation rate was developed by analytical data fitting, and takes into account the effects of deformation temperature, strain rate and straining. The simulated results show much improved predictions of the plastic flow and microstructural evolution during high temperature deformation. The CAFE code was also proved to be capable of simulating discontinuous phenomena and handling complex physical changes.