PSI - Issue 28

Mohamed Ali Bouaziz et al. / Procedia Structural Integrity 28 (2020) 393–402 M.A. BOUAZIZ et al/ Structural Integrity Procedia 00 (2019) 000–000

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(a) (b) Fig. 3. (a) Crack extension history. (b) Sample mesostructure obtained by the nozzle trajectory during printing. The green points depict the position of the crack tip for each analyzed loading step. A zoom was operated on the region of interest observed under the microscope and in which the kinematic fields were measured by DIC (see one example of longitudinal strain field at the end of the test). By focusing on the second part of the crack extension history (from step 660 on), it is noticed that the crack growth is slow and discontinuous. The discretization of the domain adopted in the location method may be the cause of these discontinuities. The distance between two nodes in this FE model was 12 µm, which induced a constant level ∆ a if the real propagation step was less than that distance. An interpolation of the values of the identification error about the minimum level provides a position that is generally located between two nodes of the mesh. As expected from Figure 2, the variation of the error as a function of crack tip position was parabolic. A parabolic fit was performed for every loading step (Figure 4(a)), and the crack tip position was assumed to be that of the minimum of the interpolated identification error. Figure 4(b) shows the effect of this enhanced method on the crack extension measurements.

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Fig. 4. Crack tip location enhancement. (a) Parabolic interpolation of the identification error (step 660). (b) Crack extension history obtained by both FE-based methods.