Estimating the S-N Curve for Steel Alloys

The information presented in this blog post is for educational purposes only. It should not be used for engineering design or relied upon as engineering advice.

The high cycle fatigue performance of a steel alloy can be characterized by an S-N curve. The high cycle fatigue approach is generally used for structures that will be exposed to 1000 or more loading cycles. The S-N curve plots cyclic stress, S, versus cycles to failure, N. The EngineeringPaper.xyz sheet below estimates the S-N curve for a steel alloy. This estimate follows the procedure outlined in the North Machine Design book [1] and accounts for the loading condition, size, surface condition, operating temperature, and desired reliability for the structure being considered. 

Even though this approach to estimating the S-N diagram for a steel alloy is useful for initial design exploration there are several limitations as discussed in the introduction section of the sheet below. It should be noted that this approach should not be used as a substitute for actual fatigue testing using the geometry, loading, material processes, and environmental conditions of the actual system being analyzed. This sheet can only be used for steel alloys and cannot be used for other materials such as aluminum since an endurance limit is assumed and many materials, including aluminum, do not have an endurance limit. Also, the correction factors used in this sheet are based on test data for steel alloys and would be different for other materials.

The S-N data generated by this sheet can be entered into a SolidWorks fatigue analysis. See the SolidWorks fatigue study tutorial video below for details of how to define a custom S-N curve in a SolidWorks fatigue study.

[1] Norton, R.L. "Machine design, A integrated approach, 5th Editi." (2013).

This S-N curve calculator for steel alloys may also be opened in a separate tab.

Estimating the S-N Curve for Steel Alloys
by u/mgreminger in EngineeringPaperXYZ