PSI - Issue 47

Artur Mugatarov et al. / Procedia Structural Integrity 47 (2023) 654–659 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

657

4

3.2. Models comparison Comparison of models (2) was carried out for the group 1 experimental data. Figure 2 shows the obtained approximations of the fatigue sensitivity curves and the corresponding damage function derivatives. Models parameters are κ =2.8195, λ =0.24205, α =0.31277, β =0.08718, m 1 =0.33851, m 2 =12.3195, q =0.25582. The determination coefficients are equal to 0.847 (WL), 0.853 (BD) and 0.879 (MM). All the approximations give excellent fit to the experimental data. The model, which was proposed by Mao and Mahadevan, gives the best fit, however it shows very slow ultimate strength reduction at the end of aggravation stage, which seems to be implausible. Fatigue sensitivity curves obtained by WL and BD models are very similar, so all of the next experimental data was approximated using Weibull-law based model. 3.3. Maximum stress value influence The influence of the stress maximum value during the cycle on the fatigue sensitivity (samples groups 1, 2 and 3) was studied (Wildemann et al. (2019, 2020)). Obtained model parameters for σ max / σ u 0 =0.4 are κ =16.952, λ =0.30610, for σ max / σ u 0 =0.6 they are κ =3.6804, λ =0.25028. It can be noted that the fatigue sensitivity curves parameters dependence on the maximum stress value is non-linear and non-monotonic. With decreasing amplitude, the form factor κ changes more than 5 times, scale factor λ changes low. Also, the decrease in the loading level leads to the sharper properties reduction at the initiation stage, while the stabilization stage is longer and has a lower damage value growth rate. Fitting fatigue sensitivity curves are shown in Figure 3.

1.0

1.0

WL BD MM

0.8

0.8

0.6

0.6

ω ' B

K B

0.4

0.4

Exp WL BD MM

0.2

0.2

0.0

0.0

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

n

n

Fig. 2. Models comparison: fatigue sensitivity curves (left side) and damage value derivative (right side)

1

1

0.4 0.5 0.6

0.8

0.8

0.4 ω ' B 0.6

0.6

0.4 K B

0.4 0.5 0.6

0.2

0.2

0

0

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

n

n

Fig. 3. Maximum stress value influence: fatigue sensitivity curves (left side) and damage value derivative (right side)