PSI - Issue 28

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

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Fig. 2. Crack tip location methodology combining DIC measurement and FE modeling. The method was run for each image acquired during the tensile test on the µSENT sample so that one crack tip position was obtained for each considered loading step. The behavior of the ABS material obtained by FDM was assumed to be elastic and ort otropic. The elastic properties were as follows E 1 = 1680 MPa, E 2 = 1414 MPa, ʋ 12 = 0.37, and G 12 = 545 MPa, where the longitudinal direction of the layer is 1, and the transverse direction is 2. The crack tip was considered to be at the position giving the minimum value of the identification error as shown in Figure 2 (step3). Figure 3(a) shows the crack extension history. At the beginning of the second part of the test, the crack advanced rapidly before slowing down from step 660 on when ∆ a reached what looks like a plateau. This trend is probably due to the geometry of the specimen but also to the mesostructure of the material. The latter is highlighted by superimposing the successive positions of the crack tip (green points in Figure 3(b)) with the orientation of the filaments given by the nozzle trajectory during printing. A zoom was operated on the region of interest observed under the microscope and in which the kinematic fields were measured by DIC. The strain field shows strained zones with a linear shape at +\- 45° following the interface area of fused filaments. It exemplifies the effect of the printed mesostructure on the mechanical behavior. This figure shows that the crack progressively grew in the two filaments forming the notch root but this propagation was slowed down by a knot formed by the superposition of two corners in two successive layers. The study of the second phase of propagation shows that the FE-based method identified small crack lengths as well as larger ones.