Cellular automata finite element (CAFE) model to predict the forming of friction stir welded blanks

The main aim of the present work is to develop a cellular automata coupled finite element (CAFE) model to predict the grain size distribution during friction stir welding (FSW) and the influence of weld defects (like voids) on the forming of FSW sheets. In order to achieve this, FSW process is simulated just by applying thermal and strain-rate analytical models on the elements constituting the FSW blanks by using ABAQUS6.8 finite element (FE) code with the help of DFLUX sub-routine. A uniform grid mesh within each finite element for cellular automata to accommodate grain size is generated for the calculation. The sheet used is Al6061-T6 with a dimension of 300 × 100 × 2.1 mm. The final grain size and yield strength are predicted by generating transition rules, relating them to temperature, strain-rate and strain evolved during friction stir welding. The computed results are compared with experimental results for validation. The forming (true stress–strain) behavior was predicted for FSW blanks containing defects by two different methods and their accuracy was compared. The thermal and strain-rate models followed in this work predict the temperature and strain-rate distribution across the weld region consistently. The results are matching well with the available data. The grain size and yield strength distribution predictions through CAFE model are agreeing well with the experimental results for all the FSW conditions. The true stress–strain behavior of a FSW blank obtained from CA model (containing grain size and strength history after FSW) coincides well with the stress–strain behavior predicted from FE simulations. The CAFE model, with a stress concentration factor, successfully predicts the influence of defects on the tensile behavior. The forming behavior obtained from both the methods (METHOD 1 and METHOD 2) is coinciding well with each other, except at the initial stages of forming.

► The temperature distribution prediction is consistent with the available results.
► The strain-rate distribution prediction is consistent with the available results.
► The grain size predictions by CAFE model agree well with the experimental results.
► The effect of defect has been successfully predicted by CAFE approach.
► The tensile behavior obtained from the proposed methods agrees well with each other.