Specimen geometry for non-typical fatigue testing

[Drej]

A series of very low cycle fatigue-type tests are being carried out on a carbon steel material. The testing is not typically "fatigue" as such, in that the specimen will be cycled over many cycles of small strain. Instead, the specimen will be cycled approx 20 times under total strain limits of 10% (ie 10% strain range). The only material that is available is in billet form (300mm x 50mm x 150mm - length/thickness/width) and current testing of this type has always been carried out on cylindrical specimens with a gauge length to gauge diameter ratio < 1 (to avoid specimen buckling problems). Would anyone foresee any issues with using typical dog bone specimens of suitable dimensions to carry out testing of this type?

Cheers.


------------
See faq569-1083 for details on how to make best use of Eng-Tips.com

 

[metengr]

Yes, because you cannot compare fatigue data results obtained using this proposed specimen geometry with the current geometry you mentioned above. There are reasons for having specific specimen sizes and geometries to ensure valid test results.

If you decided to use the alternate approach you would need to run a battery of tests to validate or qualify this alternative specimen geometry by comparing the results to the current test method. Otherwise, you may be assuming incorrect results.