PSI - Issue 23

Keng Jiang et al. / Procedia Structural Integrity 23 (2019) 451–456

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Keng Jiang et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3. FE modeling and simulation

To prepare FE models, the EBSD-based modeling approach proposed by Kayser et al. (2018) is applied in this work. Fig. 2 shows a 50 μm × 50 μm × 1 μm sample model of a WC-6 wt.% (weight percentage) Co hardmetal, which is subjected to a cyclic loading. The stress ratio equals 0.1 and the maximum applied stress is 800 MPa. The model captures more details of the microstructure when compared to previous SEM-based reconstruction. Individual WC grains are separated by WC-WC grain boundaries, and each grain is assigned the realistic local orientation exported from EBSD analysis system. The application of two-and-a-half-dimensional model by extruding two-dimensional morphology by 1 μm in the thickness direction aims at suppressing side effects, e.g. the under- or overestimation because of the plane stress or strain state assumption (Chen et al. (2016)). (a) (b) (c)

applied effective stress

10 µm

Fig. 2. (a) Morphology of the microstructure of studied hardmetal sample; (b) boundary condition of FE model; (c) cyclic loading profile.

The computational formulation of damage and failure is realized by introducing a field variable. At the end of each time increment, the updated damage according to equation (1) and equation (4) is assigned to the field variable. When the predefined failure criterion is reached, its stiffness parameters listed in Table 1 and Table 2 (except Poisson’s ratio) are set to minimal values. The material is tagged as failed and nearly loses its bearing capacity. The virtual element elimination technique allows modeling the incubation and evolution of microcracks. The functionality is realized by composing the user subroutine USDFLD and connecting with the commercial FE solver Abaqus/Standard.

4. Results and discussion

(a)

(b)

(c)

Fig. 3. Simulated damage evolution process without residual stress over loading cycles : (a) = 25 ; (b) = 70 ; (b) = 142 .