m of Fatigue

hello ,everyone
I have doubt about m in the Fatigue Calculation
I see many paper about fatigue,values of m are 3-5 if the matrial is steel ,and alues of m are 8-12 if the matrial is composite.I don’t understand the dfference between the m=3 and m=4,Are they different steel matrial ?As we know if the m is different, the lifetime we calculated is different.Can you tell me how to distinguish the m,and how we choose the appropriate m .

Best Regard


Hello Ruiliang,

a value of 3 for m is appropriate for the most steel tubes appearing in offshore structures. However, there are cases, where you need a value of 4 (small thickness exponents). Please have a look at the recommended practice RP-C203 by DNV-G, section 2. This document helps you to get an overview of offshore structure fatigue calculation.

Best regards,