An S-N curve is a graphical representation of the cyclic loading, plotted as stress amplitude versus the number of cycles the material goes through before it fails.
Dewesoft offers an editor which allows you to add or modify S-N curves. The database is located in the system folder. To change the database location go to Settings -> Files and folders:
The S-N curves editor can be found in Options -> Editors -> S-N curves.
When you enter the editor, the following window appears:
Here you can add and delete S-N curves. You can also modify the existing curves to match the stress specifications of your materials.