PSI - Issue 71

Nagaraj Ekabote et al. / Procedia Structural Integrity 71 (2025) 58–65

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Table 1. Mechanical properties of AA2050-T84 alloy

Temperature ( o C)

S yt (MPa)

S ut (MPa)

E (GPa)

% elongation

S yt /S ut

-20 24 200

520 473 490

605 564 540

9.9 12.5

68.5

0.86 0.84 0.90

75 65

8.7

2.2. Load vs. CMOD curves The CT specimen is loaded through holes in the y-direction, which is perpendicular to the crack length termed as Mode-I loading. A notch lesser to a/W of 0.5 is machined in CT specimens. Further, the fatigue load is applied to get sharp crack tip in CT specimens to attain the final a/W of 0.5. The clip gauge is attached at the knife edges of the CT specimen and the tensile load is applied gradually through holes. Correspondingly, the load vs. CMOD values were recorded and plotted. The test set-up for CT specimen and the recorded load and CMOD curve at 200 o C is shown in Fig. 2. Similarly, the load vs. CMOD curves were recorded for other temperatures. These values were further processed to obtain the J and CTOD of the alloy as per ASTM 1820 and BS 7448. 3. Numerical analysis details A CT specimen with the identical dimensions mentioned in Fig. 1 is considered for numerical analysis. ABAQUS 6.14 software is used to carry out the elastic-plastic fracture analysis. Upper half of the CT specimen is modelled in ABAQUS 6.14, owing to the symmetry of the specimen and is shown in Fig. 3. The properties of AA2050-T84 mentioned in Ekabote et al., (2022), Ekabote and Kodancha (2022) were assigned for the model. 20-noded brick elements with reduced integration were used for meshing the model. Very finite and smaller elements near the crack surroundings were assigned to ensure finer plasticity distribution, resulting in accurate measurements of J and CTOD . Along the crack ligament length, the y -symmetry boundary condition and the tensile load along the hole is applied as shown in Fig. 3. The J is computed by taking 5-counters at crack surrounding and averaging the last 3 counters. A detailed procedure to obtain J is mentioned in software and discussed in the Ekabote et al., (2022).

(b)

(a)

Fig. 2: (a) Experimental testing of CT specimen (b) Load vs. CMOD curve @ 200 o C.

Fig. 3: Symmetrical CT model with boundary conditions.