Fatigue Testing, effect of test frequency 1

[brianvh]

Does anyone know where I can get info on the effect of test frequency on fatigue testing? It is my understanding that it has an effect on plastic and cast iron but only at high frequencies. But, I don’t know what a high frequency would be, over 100 Hz or 1000 Hz or higher.

 

[ArtFabrication]

Contact StressWave Inc. In Kent, Wa

 

[TVP]

I meant to post something sooner, so I hope this is still of use to you. The following information is taken from the "Ultrasonic Fatigue Testing" section of ASM HANDBOOK Volume 8 Mechanical Testing:

In general, testing by ultrasonic fatigue (~ 20 kHz)produces fatigue data that differ only slightly from those observed at more conventional frequencies. Some data reveal a shift in the ultrasonic fatigue stress-life data (S-N) for a given stress level toward increased lifetimes relative to conventional frequency results. Other reports indicate no shift in the S-N behavior. Most reports indicate that fatigue degradation at ultrasonic frequency occurs by the same sequence of events as at conventional frequencies, namely, saturation of rapid hardening, formation of persistent slip bands, formation and growth of intrusions, and crack propagation.

Materials that exhibit clearly defined endurance limits at conventional frequencies usually exhibit endurance limits at similar cyclic stress amplitudes at ultrasonic frequencies. Similarly, materials that exhibit threshold stress intensities for fatigue crack growth at conventional frequencies also exhibit this behavior at ultrasonic frequencies. Shifts in S-N fatigue behavior to higher stress levels and longer lifetimes or da/dN behavior to slower crack growth rates do not occur for all materials tested at high frequency. Recent testing shows that the effect of frequency on S-N and da/dN performance is primarily a function of the microplasticity and slip character of the material under test.

I would add that this applies basically to metals. I am not sure what the upper frequency limit is for fatigue testing of plastics before hysteric heating and other effects make the results questionable. Corrosion fatigue can be a problem area-- the duration of exposure of the crack tip to the corrosion environment has been shown to have an effect on fatigue performance. You can find more information on fatigue testing in Volume 8 and Volume 19 Fatigue and Fracture, which are available from ASM International at

http://www.asminternational.org

.

 

[borjame]

I think you're talking about failure due to HCF or high cycle fatigue, where a part fails below yield. It affects most materials I'm familiar with (metals, not just iron). A high cycle would be well over 1000 Hz probably a magnitude higher. Try looking up info on Campbell and Goodman diagrams, or Miners Rules. Miners Rules in particular will deal with cyclic loading in the region between LCF and HCF.

 

[CoryPad]

High cycle fatigue refers to the total number of cycles, not the cycle frequency.

For most metals, there is no frequency effect up to ~ 100 Hz. After that, it may become an issue.