Strain controlled Fatigue testing - what strain rate?

[will123123]

I am going to run some ambient temperature strain controlled fatigue testing (for the first time) on stainless steel (13-8PH). I am working in accordance to ASTM E606-04, but while the standard recommends testing to a constant strain rate, it does not advise a value. Could anyone provide guidance on appropriate strain rate?

Also what is the best way to determine a good starting point for the strain amplitudefor the first specimen.

Thank you.

 

[metengr]

will123123;
It may help to understand what you intend to do with the strain- life fatigue results. For example, what is the application for the stainless steel in service?

 

[TVP]

Conventional fatigue testing is done on servohydraulic load frames that cycle around 20-50 Hz. 1000 Hz machines have been developed and available from MTS. More recent testing in the very high cycle fatigue (VHCF) regime has been done on resonance equipment that cycles at even greater frequencies. Here are some links that you might find helpful:

http://www.mts.com/en/products/application/materials-testing/metals/high-cycle-fatigue/index.htm

http://www.lbl.gov/ritchie/Library/PDF/ROR-HCF_99.pdf

http://144.206.159.178/ft/718/555701/12396352.pdf

 

[metengr]

In addition to the above information, for strain-life fatigue testing one is looking at low cycle fatigue applications, in lieu of high cycle fatigue applications, where the stress-life approach is more common.
For the OP, there is no standard value for strain rate. What I would suggest is look at the purpose of the fatigue testing and decide on a strain range. Once this is known, you can select a frequency as mentioned above, and know you have a defined strain rate (strain/cycle, cycle/second). The unknown is total strain range and this must be defined by the service application.

 

[will123123]

The reason for the testing, as mentioned by Metengr is to investigate the low cycle fatigue response of the material. Previously I have only carried out stress/load controlled testing.
The intention is to establish values for the following parameters to enable more accurate FEA modelling of life limits for highly loaded components: -
Cyclic strain hardening coefficient and exponent.
Fatigue strength co-efficient and exponent
Fatigue ductility coefficient and exponent