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论文题目： Multi-scale crystal plasticity finite element simulations of the microstructural evolution and formation mechanism of adiabatic shear bands in dual-phase Ti20C alloy under complex dynamic loading

发表时间：Available online 21 June 2020

刊源：Journal of Materials Science & Technology 59 (2020) 138–148 [ 点击下载PDF ]

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A multi-scale CPFEM method is proposed for extracting load infor-mation from the macro model, and then progressively applying thisinformation to the micro grain models. Firstly, microregion of interest is selected from the interior of the ASB, anda set of the micro region boundaries is established in LS-DYNA. Secondly, a model with the same size as the micro region of interest,and a finer mesh method (than previously employed) is established. The region near theedge of Ti20C sample was selected as the observation area, andSEM and EBSD measurements were performed after the edge ofthe sample was bombarded uniformly with focused ion beam.

Fig. 4. (a) Process of extracting load information from the macro to the micro model and (b) phase distribution and grain orientation distribution based on the grainmicrostructure.

The microstructure inside the ASB is characterized by means of TEM (see Fig. 7(a) for the obtained image). Micro regions consisting of multi-phase and multi-grain regions with large residual stresses occur in the ASB. Details of the grain orientation and grain boundary are captured accurately by means of PED (the measured grain orientation distribution is shown in Fig. 7(b)). Using the soft-ware Image-Pro Plus V6.0 reveals that the shapes of grains inside the ASB can be divided in two types: Type 1: elongated large grains with length of ∼4 nm (i.e., 2–5 times the grain width) along the ASB direction. The intragranular orientations are basically the same; Type 2: small equiaxed grains (diameter: 500 nm).

Fig.7. Microstructure inside the ASB of TI20C: (a) TEM image and diffraction pattern; (b) grain orientation distribution captured by means of PED.

The adiabatic shear deformation of the microcrystalline grains was investigated by using the crystal plastic finite element simulation method. Two α-phase grains (Gα1, Gα2) and a β-phase grain (Gβ1) are chosen as research objects. The elements at the centroids of the grains are referred to as Eα1, Eα2, and Eβ1, respectively. These elements all undergo yielding, and the effective stress decreases with continued deformation, indicating that stress softening has occurred in these elements during the plastic deformation process. The softening effect is strong in Eα1 and relatively weak in Eα2 and Eβ1. Therefore, the stress of each element decreases quickly due to the effect of thermal softening, which may eventually lead to adiabatic shear failure.

Fig.8. Simulation results of the micro model: (a) schematic showing the positions of grains Gα1, Gα2, Gβ1, and the centroid elements Eα1, Eα2, Eβ1; (b) effective stress historyof the centroid elements.