Section 5 Approval of alloy steel used for intermediate shaft material

5.1.1 The requirements of Pt 5, Ch 6, 5 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, 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.

5.2.1 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 τ_c given by the formulae in Pt 5, Ch 8, 2.5 Limiting stress in propulsion shafting.

5.2.2 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.

5.2.3 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 6.5.1 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.

5.2.4 The measured torsional fatigue strength for continuous operation, τ_c, and torsional fatigue strength for transient operation, τ_t, are to be equal to or greater than the values given by the following formulae:

Where

5.3.1 The steels are to have a degree of cleanliness as shown in Table 6.5.2 Cleanliness requirements when tested according to ISO 4967 method A. Representative samples are to be obtained from each heat of forged or rolled products.