PSI - Issue 37

Jin Kim et al. / Procedia Structural Integrity 37 (2022) 282–291 Kim et al./ Structural Integrity Procedia 00 (2021) 000 – 000

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Johnson-Cook (J-C) plasticity model is commonly used to represent the mechanical deformation characteristics in the machining of aluminium alloys: = ( + ) (1 + ( ̇ 0̇ )) (1 − ( − − ) ) , (1) where is the von Mises flow stress, is the plastic strain, ̇ and 0̇ are the strain rate and reference strain rate, respectively in s -1 , , , , , , are empirical constants, is the melting temperature and is the transition temperature. Johnson-Cook damage model was used to simulate a shear failure model which initiates and propagates the chip formation process. The failure strain is obtained as: = [ 1 + 2 ( 3 ( ))] [1 + 4 ( ̇ 0̇ )] [1 + 5 ( − − )] , (2) where 1 to 5 are the damage model constants, is the mean stress and is the equivalent stress. Fracture during the turning process was modelled according to the cumulative damage law given in ABAQUS/Explicit software: = ∑ ∆ , (3) where ∆ is the increment of equivalent plastic strain and is the equivalent strain at fracture. We use a similar modelling strategy to represent the deformation and damage as in previous studies of MMCs by Zhou et al. (2010). The workpiece was discretised using linear coupled temperature-displacement hexahedral elements with reduced integration (C3D8RT) available in ABAQUS. To allow material removal, the element deletion technique was used, with a maximum degradation of 0.9 and distortion length ratio of 0.1. The cutting tool was modelled with discrete rigid elements, effectively assuming no wear, which is akin to using a PCD tool. 4. Results and discussions 4.1. Cutting force results for Exp. 1 & 2 The average cutting forces in three orthogonal directions (tangential, radial, feed in terms of 217XG workpiece) using a carbide tool are shown in Fig. 2.

The graphs show average forces in the three orthogonal directions during UAT when compared to CT. At lower cutting speeds, the reduction in cutting force in UAT is larger. In general, the amount of reduction was intensified at Fig. 2 Average cutting forces results by varying at =0.1 mm (left) and varying at = 30 m/min (right) for 217XG