# Thread: Determining Ductility and also Fatigue Strength

1. ## Determining Ductility and also Fatigue Strength

I'm trying to come up with an fatigue strength value for Haynes 230 at 1600F. I can't find a published value anywhere so I've been researching methods to calculate it. I found the Manson-Hirschberg Universal Slopes Equation which predicts strain using ultimate tensile strength, elastic modulus, cycles to failure, and % Reduction in Area.

I guess the 2 questions that arise are: Can I calculate % Reduction in Area from Poisson's Ratio and % Elongation? Once I calculate strain using the Universal Slopes Equation can I use that to calculate the stress and use that number as a fatigue strength?

Attached is a pdf with the calcs I've done. Not sure if I'm off my rocker on this.

2. I assume you first checked here...
http://www.haynesintl.com/230HaynesAlloy.htm

3. Yes, I've used the Low Cycle Fatigue data there as a check for the strain I calculated using the Universal Slopes Equation and it checks out.

I guess the important question is whether or not calculating Stress from the Total Strain Range and Elastic Modulus is a valid way to determine the fatigue strength.

In the end I need to know if the stresses I'm seeing during vibration simulation are going to be problematic.

4. If fatigue life is going to be an issue for your application, then the only sure way is destruction testing to build a database of conditions and results. it is not just for the fun of seeing things break that they life-cycle-test airplane wings to destruction.

5. I will be doing vibration testing as part of my qualification plan. I'd like to have some assurance that I'll make it through the test before I start. Any thoughts on the calculations I have done?

6. Nicely presented calculations and what you have done appears good, but still hard to say what is going to happen with actual testing. Still too many unknowns to form much of an opinion. To be fair, not an area I have had a great deal of experience in and certainly not at that elevated temp.

Try a PM to Zeke for an opinion, he seems to have had more experience in that arena -- I think.

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