Im new to fatigue analysis and I cant quite figure out what im doing wrong.

Im getting this message saying no damage (first picture) but if I run it anyway the damage plot goes way high. If I drop it to 100% its all red (second picture). So why am I getting the no damage message when there seems to be huge damage in a very short time? What am I missing?

Model is here: Dropbox - Shaft.rar - Simplify your life

Hello Conrad,

I had a look at your model and I can provide some clues.

I'd first like to make a couple of points:

I identified three things I would like to point out to you.

==> In your fatigue study, you are using Stress Intensity to evaluate the alternating stress. The minimum stress in your S-N curve is 199.999996 MPa, and the max Stress intensity is 193.3 MPa. Hence the error message

==> You defined an event with 100 million cycles. But the last datapoint in your S-N curve is for 1 million cycles. Therefore, the program cannot know wht the damage would be at 100 million cycles. the program assumes that 1 million cycles (the last point in the S-N curve) corresponds to the end of life = 100% damage. Therefore, 100 lillion cycles is 100 times more, = 100 * 100% = 10,000%

==> Be careful, the use of such curves is specifically for pressure vessels and boilers. It doesn't seems like it's appropriate for your shaft. Instead, consider the suggestions in Solution ID: S-018810 - "Fatigue curve calculation for steels" to evaluate a more realistic S-N curve.