PSI - Issue 82

Sigbjørn Tveit et al. / Procedia Structural Integrity 82 (2026) 112–118 S. Tveit et al. / Structural Integrity Procedia 00 (2026) 000–000

117

6

&' [MPa] 235.4 313.8 155.9 96.11

[-]

[MPa] ( [MPa] ) [-] ) [-]

Table 2. Model parameters.

Material

Mild steel (1) Hard steel (1)

0.0309 (2) 0.1384 (2) 0.3930 (2) 0.1433 (2)

2.411 25.86 17.31 61.86

374.1 681.1 433.0 180.9

0.35 0.35

-0.1 -0.1

Duraluminum (1) 3%C cast iron (1)

1.0

-0.04 0.08

0.35 (1) = 10 * and = = 1 were used for all materials. (2) Calculated as = ) [ ( (10 + ∙MPa) ⁄ ] + ) , according to recommendations in the FKM Guideline, where ( is the ultimate stress, and ) and ) are empirical parameters provided for different material types.

(b)

(a)

(d)

(c)

Fig. 2. Model predictions and experimental data for (a) in-phase loading, and out-of-phase loading with (b) = 22.5° , (c) = 45° , and (d) = 67.5° . The solid lines represent the generalized formulation (cf. Section 2), and the dashed lines represent the original formulation by Ottosen et al. (2008) (i.e. = 0 ). The filled markers represent the fatigue limits used to determine the model parameters. For 3%C cast iron, application of the generalized model format substantially improves the prediction accuracy, and the model closely matches the fatigue limits across the different stress angles and phase shifts. For mild steel, hard steel and duraluminum, the model captures the moderate increase of the fatigue limit as → 90 for the stress angles = 22.5° and 67.5° , but clearly exaggerates the effect for = 45° , resulting in an overestimation of the fatigue limits. The results obtained with the original model formulation (i.e. = 0 ) display an increase in %,#&' of 32.2 %