PSI - Issue 2_A

S Choudhury et al. / Procedia Structural Integrity 2 (2016) 736–743 S. Choudhury, S. K. Acharyya, S. Dhar / Structural Integrity Procedia 00 (2016) 000–000

742

7

0 10 20 30 40 50 0,000000

100 150 200 250 300 350 400

y = 94.61x + 6.429

2 )

2 )

J M‐pl (N/mm

G fr (N/mm

Gfr versus Temp

Temp=‐80C

0 50

‐100

‐50

0

50

0,250000

0,500000

Temperature (°C)

Crack Growth (mm)

Fig 11. J M-pl versus Crack growth at -80°C

Fig 12. G fr versus Temperature at varying temperatures

Table 2. Comparison of estimated G fr from two different approaches for different a/w ratio

Table 3. Estimated G fr values at varying temperatures

G fr

G fr from the slope J m-pl -Δa curve

G fr from the slope J m-pl - Δ a curve

Sl. No

Sl. No.

Temperature

a 0

a/W

For 1mm crack growth

For 2mm crack growth

1 2 3 4 5 6 7

22

336.1 307.2 310.0 323.0 295.9 209.8 54.61

1 2 3 4 5 6

22.68 22.82 25.99 24.52 27.50 27.88

0.45 0.46 0.51 0.49 0.55 0.56

308.13

306.98 331.67 306.40 330.40 277.85 244.93

277.2 379.6 382.1 336.9 273.6 232.0

0

-20 -40 -60 -70 -80

333.8

311.22 333.63 283.65 265.62

5. Conclusion

i. G fr values have been estimated for the material 20MnMoNi55 steel for different crack lengths using both graphical approach and from the slope of J m-pl method (Table 1 and Table2). It is observed using both the approaches the G fr values are very close to each other and almost constant for different a/w ratios for the material 20MnMoNi55 steel. The deviation in the estimation of G fr for varying geometries is ±17% using J m-pl method whereas for graphical approach the deviation is around ±9%. ii. The G fr values estimated from the slope of J m-pl –Δa curve for low temperature is somewhat expected as we can see from Table 3. With the decrease in temperature there has been a considerable amount of decrease in the values of G fr. Since the contribution of ductile stretch is almost negligible at -80°C so the G fr has dropped down very steeply as shown in Fig 11. As the crack growth is very low at-80°C so the G fr has been estimated from the slope of J m-pl –Δa curve at a low regime of crack growth. iii. In the lower temperature regime multiple tests and evaluation of G fr is required to characterise it. iv. A combined model consisting G fr to capture the contribution of temperature dependent ductile stretch and energy for brittle fracture can be useful to characterise fracture toughness in DBTT.