PSI - Issue 13

T.D. Joy et al. / Procedia Structural Integrity 13 (2018) 328–333 T. D. Joy et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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4. Discussion of Simulation Results and Future Work In A DAPCRACK 3D crack growth is performed by calculating the cyclic compara tive stress intensity factor, Δ K V , as given in Schöllmann et al. (2001) and comparing it with the threshold value Δ K th . The threshold for the simulations is 220N/mm 3/2 and the fracture toughness for both the simulations is set to 3700N/mm 3/2 . If unless specified in the discussion, the results from crack labelled as 2 are considered.

Fig. 4. (a) Initial crack; (b) crack fronts with inside pressure; (c) crack fronts with inside pressure and temperature boundary condition.

During all the simulations performed in A DAPCRACK 3D the crack grows till the outer surface of the Y-strainer without reaching fracture toughness at any point earlier. The simulation which had only pressure on the inner surface had a maximum Δ K V of 1396.21N/mm 3/2 in the 37 th step and it took 46 steps to reach the outer surface. On the other hand, the simulation which has both pressure and temperature loading conditions had a higher value because of the extra stress caused by the temperature difference in the model. The maximum value of Δ K V calculated in the second model is 2300N/mm 3/2 . In this case where there are two loading situations, it took the crack only 36 steps to reach the outer surface. The loadcycles needed for the crack in the model with only pressure to reach the outer surface are 598,899 and for the one with both the loading conditions are 131,931.Thus it can be concluded that compared to the other model the crack growth is faster for the model which has the additional temperature boundary condition and reaches the outer surface earlier and thereby terminating the simulation. Additionally, as seen in Fig 4 c and for crack number 1 the extra stresses cause the crack in the second model to broaden through the model while growing towards the outer surface as compared to Fig. 4 b where it was having the semi-circular shape thoughout the simulation. On the contrary, the crack 2 in Fig. 4 b broadens while growing to the outer surface. But it can be concluded that for cases with temperature both the cracks reach the outer surface earlier. Besides, as seen in Fig. 5 a and Fig. 5 b, Δ K V was more or less constant throughout the simulations.

Fig. 5. (a) Δ K V with inside pressure; (b) Δ K V with inside pressure and temperature boundary condition.