If there is no S-N curve for a steel material, we could calculate a typical fatigue life using its tensile strength (I will call it a common S-N curve, here). When calculating its endurance limit, some correction factors, so called marine factors are applied. Here I have a question. What about Notch factor?
The S-N curve from the tensile strength is usually applied to a fully reversed condition (R=-1), as far as I know. I need to see if a bolt has inifinite life or not. But it is just standard bolt and its S-N curve is not specified. So, I have to use the common S-N one. But, you know, the stress at its minimum section of the external thread is amplified so the notch factor should be considered, I think.
But someone said it does not need to be considered when checking out the endurance limit. Is it correct? I cannot imagine it in my head. If it is correct, only the normal stress affacts the material's infinite life and its stress concetration just impacts on the finite fatigue life. Is that true?
If it's not, could you please let me know how to apply the notch factor to the common S-N curve? It is based on the unnotched geomatry. Normally, notched S-N ones are used for the stress-concentrated geometry. So, I have no idea how to use the notch factor with the common S-N curve.
Thanks
Have a nice day
@Claudio Pedrazzi
Thank you for your replay and sorry for reading it late due to a sudden busy work.
Regarding the "common SN curve", what you understand is correct. A half of the ultimate strength is commonly used as the endurance limit, if there is not a specific experimental SN curve. Using the marine factors, the limit can be lowered.
However, what about notch factor? If I apply it to the limit, it is too conservitive as you know. I have no idea of it.
Oneday, I heard indirectly that the notch factor can be ignored to the typical SN curve. I cannot understand why it can be.
If you have any clues, please let me know.
Thanks and have a nice day~ :)
- Badges
- Science topic