PSI - Issue 12

Venanzio Giannella et al. / Procedia Structural Integrity 12 (2018) 479–491 V. Giannella/ Structural Integrity Procedia 00 (2018) 000 – 000

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Figure 11. Load spectrum built on K eff values.

Figure 12. DBEM Crack Growth Rates. In particular, two load cycles come out, a major cycle 0-LC1 and a minor cycle 0-LC4: the latter provides K values along the crack front lower than K ℎ for the material under analysis (2000 psi*in^0.5 at the highest temperature to be on the safe side, Tab. 1) and for the chosen initial crack. Therefore, such secondary cycle does not give any contribute during the initial crack-growth steps, providing an (slight) impact on the propagation only when the crack becomes sufficiently large, with a size whose corresponding SIFs exceed such K ℎ . The step-by-step crack propagation simulation is set up with 20 steps, each comprehensive of the following phases: • crack adder , with the crack inserted into the DBEM uncracked model; • crack loading , with the crack faces loaded by FEM stress results; • solve , with DBEM model solved and SIFs computed; • crack life , with the CGRs computed from Eq. 1; • crack extend , with prediction of the new crack front.