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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Tempered martensite microstructure. As regards it was found that the decrease in intercept 'C' when load ratio was increase to 0.5 is significant in case of steel A than steel B. This indicates that effect of 'R' ratio is significant for steel A than steel B. Table 6. 'm' and 'C' values

Material

Load ratio R=0.1 R=0.5 R=0.1 R=0.5

Paris slope(m)

Y intercept(C)

Steel A Steel A Steel B Steel B

2.353 4.008 2.223 3.363

8.59E‐8 5.39E‐10 1.03E‐7 2.28E‐9

Fig 5.a vs N (a) Steel A at R=0.1 &R=0.5; (b) Steel B at R=0.1 &R=0.5

Fig 6. ΔK vs Kmax (a) Steel A at R=0.1 & R=0.5; (b) Steel B at R=0.1& R=0.5

3.4. Effect of K max In the conventional approach, for a fatigue crack growth to propagate, ΔK is often identified as effective driving force representing intrinsic material behaviour. However in an Unified Approach, proposed by Sadananda and Vasudevan [K. Sadananda (2004)], both parameters Kmax and ΔK are considered and they contribute to two crack tip driving forces . It must be noted that both Kmax and ΔK has a threshold value which must be met for the crack to grow. From this it can be further deduced that in the case of Paris region, for crack to grow at a given growth rate, a