PSI - Issue 71

Ganesh Nigudage et al. / Procedia Structural Integrity 71 (2025) 218–225 Here, is Yield stress (MPa), is Tensile strength (MPa), ε t is total elongation(%), h o is initial specimen thickness(mm), F 0.1mm, offset is force at the intersection between the test record and a line parallel to the slope of the initial linear region with an offset of 0.1 mm (N), F m is maximum force in SP test (N), is punch displacement at maximum force (mm). The tensile properties obtained from SPT of thermal aged specimens are compared with as-fabricated condition and shown in Fig.2. Insignificant change in tensile properties was observed for the ageing time studied.

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Fig.2. Variation of tensile properties with thermal ageing (a) yield strength, (b) tensile strength, (c) total elongation.

3.2. Evaluation of DBTT by SPT

The small punch fracture energy (E SP ) was calculated from load displacement plot of SPT of as-fabricated base by integrating till displacement where force dropped to 20% of maximum value i.e. v f then it was normalized by peak load (F m ) to obtain E n (normalized energy). The normalized energy is plotted against test temperature in Fig.3. The DBTT could not be estimated because the test temperature could not reach region of lower shelf energy.

Fig.3. (a)Variation of SP fracture energy with test temperature for as-fabricated base, (b) load-displacement plots of as-fabricated base specimen at different test temperature. 3.3. Hardness Examination results The average VHN hardness of as-fabricated and 1200h aged specimens was around 220VHN and of