PSI - Issue 71

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

60

z values. 7448 = 2 (1− 2 ) 2 7448 = 2 (1− 2 ) 2

+ . . . + + + (0.46) . (0.46) +

(3)

(4)

Though, the usage of BS 7448 based CTOD is massive compared to ASTM 1820, but it is estimated by CT specimen is least found in literature. CT specimen is used in applications of aircraft critical parts crack assessments. The crack characterization in many applications may demand both J -integral and CTOD . J IC estimation from ASTM 1820 and δ IC from BS 7448 are proven characterizing parameters for many crack assessments. Hence, a comparison between CTOD estimated from different standards is essential to improvisations needed in making CTOD as a reliable fracture toughness parameter similar to J. In this work, the estimation of m, for CT, DCT and SENB are re-examined. The nature of constraint parameter, m , variation for change in strain hardening of the material designated as S yt /S ut in Equation (2) is verified for CT, DCT, and SENB. The S yt /S ut will be varied between 0.5 and 1, along with a/W between 0.2 and 0.8. Based on the nature of variation of m , for the change in a/W and S yt /S ut , new equations (if needed) will be proposed and verified for CT, DCT and SENB. Further, a comparison between CTOD estimated from ASTM 1820 and BS 7448 is carried out. Fracture toughness tests were conducted on AA2050-T84 made CT specimen to determine the J IC and load vs. CMOD curves. The experimental data further utilized to estimate the CTOD as per BS 7448 and ASTM 1820. Finally, a comparison among the CTOD from both standards for different S yt /S ut will help to realize the current state of CTOD as a fracture parameter. 2. Experimental details 2.1. CT specimen and material details The CT specimen with dimensions used for both experimental and numerical analysis is shown in Fig. 1. The dimensions of the CT specimen were in accordance with BS 7448 and ASTM 1820. A fatigue pre-cracked notch is introduced to emulate the natural crack. The thickness of the specimen and crack length were considered as 12.7 mm. The width of the specimen is taken as 25.4 mm to achieve a/W = B/W = 0.5. AA2050-T84 alloy is used for modern day transport aircraft wing parts. The crack assessment of these wing parts is essentially carried out using CT specimens. The salient mechanical properties of AA2050-T84 alloy for different testing temperatures are shown in Table 1. The stress-strain curves and properties in Table 1 are adopted from the work of Ekabote and Kodancha (2021).

Fig. 1: CT specimen.