PSI - Issue 28

Mohamed Ali Bouaziz et al. / Procedia Structural Integrity 28 (2020) 1039–1046 M.A. BOUAZIZ et al/ Structural Integrity Procedia 00 (2019) 000–000

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Table 2. DIC analysis parameters

DIC software

Correli 3.0 (Leclerc et al. 2015)

ROI size

800×1000 pixels

Element size

4 pixels

Mechanical regularization length

60 pixels (Tomičević et al. 2013) regularized sum of square differences Exact derivation of shape functions

Matching criterion Strain calculation Strain window size

Element size Figure 3 shows the longitudinal displacement and Green Lagrange strain fields measured via DIC at the surface of both tested samples for the last image acquired prior to failure. By observing the longitudinal strains fields, one notes strain fluctuations apart from the intensification due to the crack. Over virtually the whole region of interest, ellipsoidal areas of strain concentration appear thus forming a pattern whose amplitude is significantly higher than the noise floor levels. Visual inspection shows that these strain field patterns remained the same for most of the loading steps only with a change in amplitude. This pattern is not the same for the two tested samples. The zones of longitudinal strain concentrations in the 125 µm sample (Figure 3(d)) were larger in size than those observed in the 50 µm specimen (Figure 3(b)). These zones may be related to the fabrication process, and their sizes may be affected by process parameters such as the layer thickness. To study the relationship between layer thickness and strain concentration zone sizes, the latter was calculated for all loading steps.

(a)

(c)

(b)

(d)

Fig. 3. Kinematic fields at the end of the tensile tests. (a) Longitudinal displacement field for the 50µm sample (the colour bar is in pixels, 1pixel = 2.1 µm). (b) Corresponding longitudinal strain field. (c) Longitudinal displacement field for the 125 µm specimen (the colour bar is in pixel, 1pixel = 2.1 µm). (d) Corresponding longitudinal strain field.