PSI - Issue 52

Long Jin et al. / Procedia Structural Integrity 52 (2024) 12–19

17

6

Author name / Structural Integrity Procedia 00 (2019) 000–000

(1)

0.07

As-received:

/ 2 777.84 (2 ) f N σ − ×

∆ =

(2)

0.08

450 C 1000h: °

/ 2 831.72 (2 ) f N σ − ×

∆ =

The relationship between the strain amplitude and the number of reversals to failure can be expressed by the Basquin-Coffin-Manson Eq. (3). As shown in Fig. 8a, with the fatigue life increases, the strain amplitude gradually decreases, and the data has a small dispersion in a certain life range. Furthermore, aging causes a noticeable loss of fatigue life. The curves of as received and aged data are fitted and shown in Eq. (4) and Eq. (5), respectively. As depicted in Fig. 8b, the scatters of elastic strain amplitude before and after thermal aging are almost on the same straight line, however, the plastic strain amplitude is obviously lower after thermal aging, which can be understood that the differences in the low cycle fatigue behaviour are mainly caused by the different plastic strain amplitudes after aging. As listed in table 2, fatigue ductility exponent c drops evidently after thermal aging, implying a degraded elongation of the material after aging, which is in agreement with the tensile results in Fig.4. ' ' / 2 / 2 / 2 (2 ) (2 ) f b c t e p f f f N N ε ε ε ε ∆ =∆ +∆ = + (3) where, Δ ε t /2 is the total strain amplitude, Δ ε e /2 is the elastic strain amplitude and Δ ε p /2 is the plastic strain amplitude. σ f ’ is the fatigue strength coefficient, E is the Young’s modulus, b is the fatigue strength exponent, ε f ’ is the fatigue ductility coefficient, c is the fatigue ductility exponent and 2 N f is the number of reversals to failure. E σ

(a)

(b)

Fig. 8. (a) Total , (b) elastic and plastic strain amplitude versus the number of strain reversals for as-received and aged specimens

(4)

0.0828

0.508

As-received:

/ 2 ∆ =∆ +∆ = / 2 ε

/ 2 0.00428 (2 ) N ×

0.350 (2 ) N

−

−

t ε

e ε

+ ×

p

f

f

(5)

0.0979

0.557

450 C 1000h: °

/ 2 ∆ =∆ +∆ = / 2 ε

/ 2 0.00485 (2 ) N ×

0.423 (2 ) N

−

−

t ε

e ε

+ ×

p

f

f

Table 2. The detailed experimental parameters of low cycle fatigue

Parameter

’

’

σ f

b

ε

c

f

As-received

871

-0.0828

0.350

-0.508

450 ° C 1000h

970

-0.0979

0.423

-0.557