PSI - Issue 28

V. Iasnii et al. / Procedia Structural Integrity 28 (2020) 1551–1558 Author name / Structural Integrity Procedia 00 (2019) 000–000

1555

5

2     N

, p



(5)

where N is the numbers of loading cycles. According to Fig. 4, the Odqvist's parameter is linearly proportional to the lifetime and is described well by the dependence . f AN B    (6) The dependence of the dissipated energy density on the number of cycles to failure at 0 °C and stress ratio R = 0 and 0.5 were shown on Fig. 5. The dissipated energy density value corresponds to the stabilization region at the number of half-cycles to failure. The dissipated energy per cycle was calculated as the difference between the areas of loading and unloading lines under stress–strain curves by means of numerical integration. The dependence of dissipation energy density on the number of cycles to failure in the case of low cycle fatigue is described by the following empirical equation: . d f Wd W N    (7) The parameters  W d and γ, that are given in Table 1.

100 120 140 160

10

b

a

R=0 R=0,5

Power law fit (R = 0) Power law fit (R = 0.5)

3

0 20 40 60 80

1

2 N f ꞏ Δε, %

W d , MJ/m

R=0 R=0,5

Linear fit (R = 0.5) Linear fit (R = 0.5)

0,1

0 1000 2000 3000 4000 5000

1

10

100

1000 10000 N f , cycles

N f , cycles

Fig. 4. Dependence of the Odqvist’s parameter on the number of loading cycles at R = 0 and R =0.5.

Fig. 5. Dependence of the dissipated energy density on the number of loading cycles at R = 0 and R =0.5.

Fig. 6. shows the dependencies of the damage parameter on the number of cycles to failure the stress ratio R = 0 and 0.5, that were calculated by formulas (1) and (2), respectively. It should be noted, that the austenite Young's modulus E A and maximum stress σ max on the stabilization region were employed for calculating elastic strain energy density according to the formula (2). In general, the presented results could be described by power law for various stress ratios . m t f Wt W N    (8) The parameters  Wt and m in equation (8) are presented in Table 1.