PSI - Issue 60

208 S.K. Chandra et al. / Procedia Structural Integrity 60 (2024) 203–213 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000 the crack profile from the tip was selected for determination of (Fig.4) using the following equation: ( ) ∆ =( ) ∆ (1) where is the distance between the two points located at the location , and is the distance between the crack tip and the location . CTOA from the 5 −∆ data, designated as ( 5 ) here, was determined from numerical differentiation of the test generated 5 −∆ data (Schwalbe et al., 2005): ( 5 )= ∆δ 5 ∆a (2) 6

Fig. 4. 2-point method for CTOA determination.

3. Results and discussion 3.1. Selection of CTOA ( ) measurement basis Accurate measurement of CTOA requires proper selection of the length to avoid size and geometric effects (Darcis et al., 2008). For , ASTM standard (ASTM E2472, 2012) specifies a range from 0.5 mm to 1.5 mm. For the SENT and DENT specimens tested at a ramp rate of 0.006 mm.s -1 , initially three different values, namely 0.5 mm, 1 mm and 1.5 mm, were chosen, and accordingly, three measurements for CTOA were carried out on each photograph. Figures 5(a) and 5(b) present the results.

(a)

(b)

Fig. 5. Choice of CTOA measurement basis L for (a) SENT and (b) DENT geometries.