Fatigue curve for bolting

[Xianglu]

I have an application in which the fatigue cycle numbers exceeds the ASEM VIII-2 FIG 5-120, which only has maximum cycle number of 1 million. Our cycle numbers is in the range of 10 million. How should I deal with this case?


Thanks in advance.

Henry

 

[metengr]

Review ASME Section VIII, Div 2 mandatory Appendix 5, 5-120 once again. I quickly perused it and in 5-120 there is a provision to use the higher cycle design fatigue curves in 5-110 (with an appropriate stress concentration factor), depending on the specified tensile strength of the bolt material.

 

[Xianglu]

Thank you Metengr.
I noted. Now the question is: the 5-110 curve only applies to UTS<100 ksi as per 5-120(a); if I use 5-110 curve, should I assume that the high strength materials have a UTS of only 100ksi despite the fact that they (eg B7, L7) have higher strength?
Thx, Henry

 

[metengr]

Xianglu;
See paragraph (b).

 

[Xianglu]

So Metengr, you mean that (b) is stating: “High strength alloy bolts and studs MAY be evaluated ...by the methods of 5-110 using (EITHER CURVE 5-110 OR) the design curve of Fig. 5-120.1 provided:...

By checking these two curves, at 1 million, 5-110.1.1 gives a Sa of 20 ksi and 5-120.1 gives Sa of 15 ksi. I do not quite understand that 5-110 allows a higher Sa than 5-120. Would you please give me some clues?
Thanks again!

 

[metengr]

Xianglu;
Your interpretation of (b) is not totally correct. You can use the method in 5-110. However, paragraph (b) the way I understand it still requires the use of Figure 5-120.1