PSI - Issue 14

Sachin Bandgar et al. / Procedia Structural Integrity 14 (2019) 330–336 Sachin V Bandgar/ Structural Integrity Procedia 00 (2018) 000–000

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Table 5. Steel B at R=0.1

∆K

30

35

40

45

50

da/dN(mm/cycle) a(mm)

1.25 x 10 -4 17.01

3.04x 10 -4 19.97

2.79 x 10 -4 22.41

4.67 x 10 -4 24.43

4.38 x 10 -4 26.16

3.2. FCGR at load ratio of 0.5 FCGR test of steel A was conducted at constant load corresponding to ∆K value of 15 MPa*m 0.5 with a load ratio of 0.5. The plotted data of da/dN vs ∆K is shown in Fig 4. The scatter data obtained smoothened by sixth order polynomial and then fitted by power law to obtain 'm' and 'C' values. Similar procedure was followed for obtaining FCGR of steel B with a load ratio of 0.5. From the table it is evident that there is decrease in the value of 'm' for steel B than steel A at load ratio of 0.5.Whereas the value of intercept 'C' increased by one order of magnitude considerably for steel B.

Fig 3.da/dN vs ∆K (a) SteelA R=0.1; (b) Steel A R=0.5

Fig 4.da/dN vs ∆K (a) Steel B R=0.1; (b) Steel B R=0.5

3.3. Effect of load ratio In case of Steel A, FCGR test at R= 0.1 and 0.5 reveals that the value of Paris slope 'm' increases with increase in 'R' ratio. Similar behaviour is found in the case of steel B. However, the increase in the absolute value of 'm' was found to be higher (around 70% more than that of R=0.1) for steel A which has Ferrite-pearlite microstructure. Whereas in the case of steel B, the increase in 'm' value was around 50% more than that of R=0.1 which has