Tony - This site may be useful www.campusplastics.com
In most of the cases your supplier should be able to get the information. I have heard that Moldflow has wide range of material library and S-N curves for them.
Wow that was fast.
Unfortunately, it turns out that fatigue data is hard to get. You can have it measured, but
its expensive. I figured I'm probably not the first person to need this kind of information,
and find it odd that generic curves for some of the more popular commodity plastics aren't
What is "Moldflow"?
SW, as you know, has a few built in but they appear to be exclusively for metals.
I'll dig around Campus, but its like finding a needle in a haystack.
I cannot recall ever seeing S-N curves for plastics - I believe it's because fatigue failure modes of soft materials (relative to metals) are better characterized using "strain-to-failure" fatigue data, as opposed to "stress-to-failure" (typically seen on S-N curves for metals), probably because the area can change so much (compared to metals), and it may be much easier to directly measure "large" values of deflection... Additionally, I have seen reference to failure criterion where they talk about exceeding the "fatique toughness" of the material - which apparently concerns the total amount of energy it can absorb before it fails. What I'm saying is, I believe you will have to contact manufacturers directly and perhaps resort to a different failure criterion. Please let us know what you find - highly sought after!
Thanks -- that reaffirmed some of my suspicions. I did manage to find a curve for polycarbonate, however
unreliable that might be. This may be sheer coincidence, but based on the strains in my static analysis,
"gut feel" told me this part might last about 10,000 actuations (order of magnitude).
It is a simple cantilever snap -- granted a bit big -- but still a simple cantilever in plastic.
I used the curve for PC.. again, this might be just a strange coincidence, but Simulation predicts
approximately 14,000 cycles to failure.
I really just went through the paces as a learning exercise at this point. What I did find curious, however,
is that the fatigue analysis only gave what seem to be reasonable results with fully reversible loading.
Zero-based loading (such as this snap would see), always reported the max life cycles that my S-N
contained (10^8), even though stress in the static analysis is uncomfortably close to yield.
At any rate, thanks again to all who responded.
I found curves for PC, ABS, and M-PPE in a google books result (Characterization and Failure Analysis of Plastics): https://books.google.com/books?id=RJWiilJLdxYC&lpg=PA59&ots=L2OZkKFwcR&dq=s-n%20curve%20polycarbonate%20pc&pg=PA59#v=one…
you can refer to this book - Atlas of SN Curves / fatigue curve