PSI - Issue 71

Karthik K R. et al. / Procedia Structural Integrity 71 (2025) 210–217

215

Figure 8: Variation of J-integral along the crack front

J values evaluated for different cracks are given in Table 2. Lowest break-through stress reported is 137.9 N/mm 2 for a crack with a/t ratio of 0.9. It was assumed that breakthrough has happened just after crack initiation at the deepest point. From the above data, it is conservative to assume that the crack growth initiates when the J value reaches 4.8 mJ/mm 2 at the deepest point. Crack growth might have started near to the surface (subsurface) when the J value reached 4.8 mJ/mm 2, but it was not visible during testing. This value is further referred as critical J 1e. Table 2. J-integral values corresponding to Breakthrough stress for fracture test specimen Specimen details Test results (N/mm 2 ) FE analysis (mJ/mm 2 )

Break through stress

Failure stress

Thickness (mm)

*J at breakthrough (Deepest point)

*J at breakthrough (Maximum)

a/t

a/2c

Sl no.

1 2 3 4 5 6 7 8 9

7.64 7.71 7.65 5.84 7.73 3.33 7.68 3.28 7.63 3.25 3.25 7.65 7.59 7.58 6.02 5.99 9.63 9.75 9.65 9.73

0.45 0.14 0.64 0.14 0.66 0.29 0.73 0.25 0.79 0.45 0.81 0.27 0.81 0.15 0.82 0.15 0.83 0.14 0.86 0.3 0.86 0.45 0.89 0.15 0.89 0.45 0.91 0.3 0.92 0.3 0.87 0.15 0.87 0.3 0.89 0.31 0.88 0.3 0.8 0.15

208.7 193.4 203.2 193.7 192.9 172.4 173.1 162.9 152.4 176.5 151.8 134.5 137.9 166.9 158.6 161.3 168.2 175.1 162 153

217.6 209.3 213.7 209.6 205.3 196.5 198.6 194.4 185.1 191.4 195.9 209.6 188.9 215.8 211.7 218.6 211 204 201.3 202

63.57

63.57

60.1 59.9

60.1

66.12 37.38 58.24 22.28 34.42

37.38 42.61 20.11 34.42 34.89 10.36 14.81 22

22

34.89

10 11 12 13 14 15 16 17 18 19 20

11.703

17.85 11.56

8.34

15.687

15.687

8.99

13.27

4.8

6.76

17.78

19.31

34.4

34.4

18.89 23.62 34.08

21.24 25.98 34.08

Similarly, FE analyses were carried out for LUL test specimens at peak stress also, results are shown in Table 3. Table 3. J-integral values corresponding to maximum stress of LUL test specimen