PSI - Issue 60

K. Mariappan et al. / Procedia Structural Integrity 60 (2024) 444–455 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

452

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the transition to long range stresses occurs earlier at 823 and 873 K as compared to that at lower temperatures during prior plastic deformation [Vijayanand et al (2011)].

Type 316 L(N) SS 3x 10 -3 s -1

(a)

1600

(b)

Type 316 L(N) SS 3x 10 -3 s -1

0.9

300 K 823 K 873 K

1500

0.8

0.7

K 1

1400

n 1

0.6

1300

0.5

300 K 823 K 873 K

1200

0.4

0

10

20

30

40

50

0

10

20

30

40

50

Fatigue Life Fraction (% N f )

Fatigue Life Fraction (% N f )

Type 316 L(N) SS 3x 10 -3 s -1

(c)

Type 316 L(N) SS - 0N f 3x 10 -3 s -1

(d)

6

6.0

0

-6

5.5

K 2

n 2

-12

-18

5.0

300 K 823 K 873 K

300 K 823 K 873 K

-24

4.5

0

10

20

30

40

50

0

10

20

30

40

50

Fatigue Life Fraction (% N f )

Fatigue Life Fraction (% N f )

Fig. 9 Variation of Ludwigson parameters (a) K1, (b) n1, (c) K2 and (d) n2 with varying prior fatigue life fractions at 300, 823 and 873 K.

3.3.2. Variation of Voce Parameters with Prior Fatigue Damage The physical significance of Voce equation is that it exhibits a saturation in stress values at high strains. Thus, Voce relation better describes the flow curves, which exhibit saturation in the  - ε p curve. Figure 10a shows the variation of Voce parameters  i and  s and Fig. 10b shows that of n v for the 316L(N) SS exposed to various prior fatigue damage up to 0 N f , 0.05 N f , 0.1 N f , 0.3 N f and 0. 5N f at 300, 823 and 873 K. Choudhary et al (2001) observed that both Voce and Ludwigson equations can describe the flow behaviour of 316L(N) SS with equal confidence between 523 and 773 K; however, at higher temperature up to 873 K, Voce equation was found to be more suitable. Vijayanand et al (2011) and Girish et al (2007) in their study on Titanium bearing modified austenitic stainless steel and 316L(N) SS respectively found the Voce equation to be more accurate at higher temperatures up to 1023 K. In the present study both Ludwigson and Voce relations could be applied with equal confidence at 823 and 873 K The recovery stage designated as stage III in the θσ - σ plot (Fig. 7a) can be associated with the parameter n v of Voce equation. The value of n v can in turn be associated with various mechanisms controlling recovery. High slope observed in stage III was indicated by increase of absolute values of n v with the increase in the amount of prior strain cycling.