PSI - Issue 68

Alen Marijančević et al. / Procedia Structural Integrity 68 (2025) 1203 – 1207 A. Marijancˇevic´ et al. / Structural Integrity Procedia 00 (2024) 000–000

1205

3

(a)

(b)

Fig. 1: Intermediate shaft: (a) Campbell diagram, (b) Shear stresses from steady state analysis.

    

     ,

     c 11 0 0 c 41 0 0 0 c 22 − c 32 0 c 52 − c 62 0 c 32 c 22 0 c 62 c 52 c 41 0 0 c 44 0 0 0 c 52 − c 62 0 c 55 − c 65 0 c 62 c 52 0 c 65 c 55

    

m 11 0 0 m 41 0 0 0 m 22 − m 32 0 m 52 − m 62 0 m 32 m 22 0 m 62 m 52 m 41 0 0 m 44 0 0 0 m 52 − m 62 0 m 55 − m 65 0 m 62 m 52 0 m 65 m 55

M =

C =

(1)

In the preliminary analysis, a torsional steady state analysis was performed, while the influence of flexion cycles was included in such a way that sailing in a calm sea was assumed, whereby due to the specific load of the deformed ship’s hull as explained in Murawski (2005), there was a stationary deformation of the elastic line of the propulsion shaft as shown in Fig. 2(a)

2.3. Low and high cycle fatigue criteria assessment

The DNV class guideline DNV (2021) distinguishes 4 cases of loading of the thrust shaft of large ships. The first refers to the change of load from zero to full load and back to zero. It is expected that the thrust shaft should withstand 10 3 to10 4 cycles during operation. The shaft in this case should be checked for low cycle fatigue (LCF). A commonly used equation that describes the low-cycle fatigue behavior is the Co ffi n-Manson relation Cazin et al. (2020). Based on experience, it is known that axial stresses in direct coupled propulsion plants can generally be neglected. In this case of loading, it is also allowed to ignore bending stresses. Repetitive nominal peak torsional stress should meet the condition: τ max = ( τ + τ v ) max ≤ σ y 2 SK L (2) where σ y is yield strength, S = 1 . 25 is a safety factor, and K L is a component influence factor. In this study a forged carbon steel JIS G3201 SF 590 A is selected with ultimate tensile strength σ B ≥ 590 N / mm 2 and yield strength σ y ≥ 295N / mm 2 . According to DNV (2021), bending is expected to contribute to High Cycle Fatigue (HCF). In this case a HCF criterion  τ v τ f  2 +  σ b σ f  2 ≤ 1 S 2 (3) have to be fullfiled, where τ v is nominal vibratory torsional stress for continuous operation, τ f is high cycle torsional fatigue strength, σ b is nominal reversed bending stress amplitude, σ f is high cycle bending fatigue strength and S is