PSI - Issue 60

Chinnam Sivateja et al. / Procedia Structural Integrity 60 (2024) 245–255 Sivateja et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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MPa·m^0.5; in contrast, the CMAS samples showed a Kc value of 26.5 MPa·m^0.5. Notably, these fracture toughness values fall within the range of reported values for 2024-T3 alloy in the literature (MIL-HDBK-5J, 2003). However, these values are notably lower than the plane stress fracture toughness. In cases of thin specimens, crack growth in the vicinity of failure may involve stable tearing. This lower fracture toughness estimate could be attributed to challenges in accurately measuring and distinguishing such stable tearing regions during SEM analysis. Nonetheless, the distinct fatigue surfaces confirmed the reported minimum fracture toughness values. The Stress Intensity Factor (SIF) for both CAA and CMAS is most pronounced at angles of 0 and 180 degrees, as shown in Fig. 7, corresponding to the width side of the specimens. It may have been caused by the unstable crack followed by failure in the width side once the critical SIF (fracture toughness) is reached.

Fig. 6. Thumbnail crack sites of (a) CAA and (b) CMAS specimens tested at σ max of 350 MPa

Table 3. Fracture Toughness calculation from the Thumbnail dimensions of specimens Al 2024-T3 σ max c K c

a (µm)

(MPa)

(µm)

(MPa.m1/2)

Specimens

CAA

350

1095

3864

23.9

CMAS

350

987

3576

27.5

Fig. 7. Variation of the Stress Intensity Factor on the crack front of CAA and CMAS- AA, at σ max of 350 MPa

In both CAA and CMAS-AA specimens, cracks initiate at the surface and subsequently propagate in a thumbnail like manner, as illustrated in Fig. 8. These initiated cracks extend outward in thickness and width directions, as depicted in Fig. 8(a). Further progression reveals striation marks within this region, as displayed in Fig. 8(b); notably,