PSI - Issue 28

Florian Vlădulescu et al. / Procedia Structural Integrity 28 (2020) 637–647 Vl ă dulescu and Constantinescu / Structural Integrity Procedia 00 (2019) 000–000

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For the three analysed cases of crack propagation, starting from an initial crack of 50 mm, the total deformations of the bracket are shown in Fig. 9. Two concentrated forces of 500 kN each are applied on the external edges of the two holes, opening the crack. The symmetric crack propagates, as expected, along the axis of symmetry. The 30º off axis crack (Fig. 9b) turns for the initial propagation as predicted by the MTS criterion and then, following the principle of local symmetry, propagates parallel to the axis of symmetry of the bracket. The 60º off-axis crack (Fig. 9c) cannot propagate at this force.

a) c) Fig. 9. Total deformation after SMART crack propagation: a) symmetric; b) 30º off-axis; c) 60º off-axis. b)

The distribution of the stress intensity factors along the crack front can be plotted in global views for each contour or in the Graph windows for all contours, that is steps in crack propagation, starting from the Contour Start value and ending at the Contour End value; representation is done from point 1 to point 2 (both being on the free surfaces) along the bracket thickness on the abscissa. SMART uses the number of contours as a reference to determine the remeshing volume and 4 to 6 contours are usually used; here 6 contours were used. During crack propagation for 3-D crack geometry, every node along the crack front has the same number of contours. In Fig. 10 are given in a global view the Mode I SIFs for a symmetric crack and a 30º off-axis crack, suggesting that SIFs remain mostly constant along the crack front after crack propagation. For the inclined crack SIFs are smaller as in mixed mode energy is released to eliminate Mode II.

a) b) Fig. 10. Variation of Mode I SIFs along the crack front after SMART crack propagation: a) symmetric; b) 30º off-axis.

However, it is to be mentioned that the obtained SIFs values are greater than the imposed fracture toughness K Ic = 800 MPa√mm of the material. This issue must be further analysed, as it is not clear if the cause is due to data input inconsistency or initial mesh refinement along the crack front.