PSI - Issue 28

J. Xue et al. / Procedia Structural Integrity 28 (2020) 1047–1054 Author name / Structural Integrity Procedia 00 (2019) 000–000

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failed elements from the global finite element model. Detailed crack profiles predicted by the DWTT bending and tension models are compared in Fig. 3. The crack profile is very similar in both cases. DUCTCRT is short for DUCTile damage initiation CRiTerion, and it’s defined as the ratio of effective plastic strain to the initiation strain ( ̅ � / � ). The initiation strain is defined in equation (2) as discussed in Section 2.

Fig. 3. Comparions of the crack profiles predicted by FEA and the interupted DWTT specimen

To measure CTOA, a python script was developed to automate the process of calculating CTOA at every increment of crack extension. The python script records the coordinates of crack tip and crack opening displacement at each time increment as shown in Fig. 4. The crack opening displacement was measured at a distance behind the crack tip, and the CTOA was calculated as CTOA = 2*arctangent (COD/2 / distance behind crack tip). Distance behind crack tip is 1 mm by default.

Fig. 4. Illustration of the method to determine CTOA

CTOA predicted using the current models agrees well with the test result as shown in Fig. 5. CTOA is consistent in DWTT specimens under bending and tension and both cases exhibit steady-state propagation. For the DWTT bending model, the CTOA on the surface is higher than that in the interior, which is in agreement with the experiments and consitent with the FEA results using explicit the X-Wmodel discussed in previous research by Simha et al. (2014). However, for the DWTT tension model, there is no signifiant difference between CTOA on the surface and CTOA in the interior.