PSI - Issue 14

Digendranath Swain et al. / Procedia Structural Integrity 14 (2019) 207–214 Author name / Structural Integrity Procedia 00 (2018) 000–000

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visible in DIC strain fields. Therefore, the AE signals seen prior to the visible crack in DIC strain field were correlating with the growing nature of an inhomogeneity or void inside the specimen. Therefore, it can be ascertained that whenever microscopic growth of any defects occurs it is captured with AE much ahead of its surface appearance. The severe non-linearity of all AE parameter observed as compared to the non-linearity seen in the parameters extracted from DIC is evidence to the above inference.

Fig. 4. Correlation of AE data with DIC for SCT specimen-1; (a) comparison of CCOD measured with DIC and cumulative hits obtained in AE (b) comparison of strain fields in the vicinity of the crack tip and AE signal amplitudes, (c) the cumulative AE energy, and (d) cumulative AE duration measured during the entire loading process. Here the following nomenclature has been used; 1-initiation of internal yielding, 2-stable internal crack growth, 3- severe plastic deformation, 4-unstable crack growth and failure.

Fig. 5. (a) DIC longitudinal strain map for PT specimen-1 at just before failure, (b) photograph of the PT specimen-1 failure through severe necking, (c) DIC longitudinal strain map for PT specimen-2 at 1459 MPa, (d) photograph of the cracked PT specimen-2 without any necking.