Tables 2.5 and 2.7 (D1.1-2008) show various configurations and geometries that are categoried as A, B, C, etc.

Once the engineer has determined which fatigue category applies and once he has determine the stress range (highest stress minus the lower stress) and the number of cycles requires fatigue to be considered, the appropriate "curve" is selected from the S-N graph. One thing to remember is that the stress range does not have to involve a complete stress reversal (compression to tension to compression) for fatigue to become a factor in the design.

Best regards - Al

Hi

I don't think there is a specific definition for each stress category. Rather, the stress category is chosen by reading the description, and inspection of the illustration. By knowing the particular stress category, the designer knows which design equations to use, and what "constants" etc to use for those calculations.

Hope that helps.

Regards
Niekie