Section 6 Approval of alloy steel used for intermediate shaft material
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 2 Machinery and Engineering Systems - Part 3 Transmission Systems - Chapter 2 Shafting Systems - Section 6 Approval of alloy steel used for intermediate shaft material

Section 6 Approval of alloy steel used for intermediate shaft material

Parent topic: Chapter 2 Shafting Systems

6.1 Application

6.1.1 The requirements of Vol 2, Pt 3, Ch 2, 6 Approval of alloy steel used for intermediate shaft material are, in addition to the requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022, Ch 5, 3 Forgings for shafting and machinery, to be applied to the approval of alloy steel which has a minimum specified tensile strength greater than 800 N/mm2, but, not exceeding 950 N/mm2 intended for use as intermediate shaft material.

6.2 Torsional fatigue test

6.2.1 A torsional fatigue test is to be performed to verify that the material exhibits a similar fatigue life to conventional steels. The torsional fatigue strength of the material is to be equal to or greater than the permissible torsional vibration stress τc given by the formulae in Vol 2, Pt 5, Ch 1, 3.2 Limiting stress in propulsion shafting .

6.2.2 The test is to be carried out with notched and unnotched specimens respectively. For calculation of the stress concentration factor of the notched specimen, fatigue strength reduction factor β should be evaluated in consideration of the severest torsional stress concentration factor in the design criteria.

6.2.3 Test procedures are to be in accordance with Section 10 of ISO 1352 and the test conditions applied are to be in accordance with Table 2.6.1 Test Condition. Mean surface roughness is to be less than 0,2μm Ra with the absence of localised machining marks verified by visual examination at low magnification (x20) as required by Section 8.4 of ISO 1352.

Table 2.6.1 Test Condition

Loading type Torsion
Stress ratio R = -1
Load waveform Constant amplitude sinusoidal
Evaluation S-N curve
Number of cycles for test termination 1x 107
6.2.4 The measured torsional fatigue strength for continuous operation, τc, and torsional fatigue strength for transient operation, τt, are to be equal to or greater than the values given by the following formulae:
where
Ck = a factor for different shaft design features, see Table 1.3.1 Ck factors , Vol 2, Pt 5, Ch 1, 3.1 Symbols and definitions 3.1.4
Cd = size factor, see Vol 2, Pt 5, Ch 1, 3.1 Symbols and definitions 3.1.1
σu = specified minimum tensile strength of the shaft material, in N/mm2
r = speed ratio, N/Ns, see Vol 2, Pt 5, Ch 1, 3.1 Symbols and definitions 3.1.1

6.3 Material requirements

6.3.1 The steels are to have a degree of cleanliness as shown in Table 2.6.2 Cleanliness requirements requirements when tested according to ISO 4967 method A. Representative samples are to be obtained from each heat of forged or rolled products.

Table 2.6.2 Cleanliness requirements

Inclusion group Series Limiting chart diagram index l
Type A Fine 1
Thick 1
Type B Fine 1,5
Thick 1
Type C Fine 1
Thick 1
Type D Fine 1
Thick 1
Type DS - 1
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