PSI - Issue 14

Viswa Teja Vanapalli et al. / Procedia Structural Integrity 14 (2019) 521–528 Viswa Teja Vanapalli/ Structural Integrity Procedia 00 (2018) 000 – 000

526

6

Table 2. Analyses of Three-point bend specimens: geometrical details; cohesive zone parameters and ‘q’ parameter. Specimen B (mm) B N (mm) a 0 /W W (mm) Cohesive Energy, G (kJ/m 2 ) Peak Stress, T (MPa)

‘q’ parameter

T082B T082C T083A T083B T085B T122A T123B T123A T125C T125B T252B T252A T253A T253B

8.18 8.14 8.12 7.90 8.06

6.98 6.76

0.244 0.305 0.347 0.356 0.513 0.275 0.354 0.362 0.430 0.505 0.189 0.200 0.342 0.354

25.10 25.08 25.06 25.06 25.06 25.08 25.08 25.08 25.08 25.02 50.18 50.14 50.20 50.28

220 220 220 220 220 220 220 220 220 220 220 220 220 220

1275 1300 1300 1275 1275 1700 1600 1625 1825 1700 1700 1750 1825 1775

0.32697 0.33388 0.31896 0.32574 0.30957 0.30772 0.30764 0.30341 0.28148 0.26774 0.27268 0.26977 0.24349 0.23761

6.7

6.46 7.00

12.68 12.58 12.72 12.64 12.48 25.32 25.18 25.24 25.20

10.14 10.12 10.12 10.14 10.10 20.80 20.50 20.52 20.46

Table 3. Analyses of Straight pipe with through- wall cracks: geometrical details and ‘q’ parameter. Specimen Outer diameter (OD) mm Wall thickness (t) mm Outer Span Mm Inner Span Mm

Crack angle (2θ)

‘q’ parameter

SPBMTWC8-1 SPBMTWC8-2 SPBMTWC8-3 SPBMTWC16-1 SPBMTWC16-2 SPBMTWC16-3

219 219 219 406 406 406

15.15 15.10 15.29 32.38 32.15 32.36

4000 4000 4000 5820 5820 5820

1480 1480 1480 1480 1480 1480

65.6 93.9

0.31878 0.328761 0.351526 0.332117 0.330341 0.349647

126.4

96

126.3 157.8

3. Variation of cohesive zone parameter ‘T’ with crack tip stress triaxiality

3.1. An Empirical Relation

A significant dependency of peak stress ‘T’ on stress triaxiality is observed in Fig. 6a. It is also observed that ‘T’ increases with the increase in constraint level. The value of T saturates close to 1800 MPa for SA333 Grade 6 Steel for a value of ‘q’ less than 0.26. Similarly, the value of ‘T’ saturates close to a value of 1000 MPa for ‘q’ more than 0.36. The equation of best fit sigmoidal curve between these two parameters is as follows.

, where 0.24 < q < 0.35

(5)

Fig. 6. (a) Plot of ‘q’ vs. peak stress (T) for SA333 Grade 6 steel ; (b) Typical peak stress values at different Z scores for ‘q’ value of 0.31878 .