Fatigue EFR stress

[PriamEngineering]

When looking at fatigue problems. I have often been asked to present to non analysts and managers. The normal method I used to employ was to plot critical points on a Goodman Diagram. Of course this relied on the audience understanding how a Goodman diagram was constructed. Which I am sure you will agree is not always the case. The story of the “Emperors new clothes” applied and I felt that a large proportion of the audience just didn’t get the message and didn’t want to appear stupid by admitting so.

To better engage with the audience I have been experimenting with dispensing with the Goodman approach and using the ‘Equivalent Fully Reversed’ (EFR) stress approach. This has two advantages.
1. It allows the finite element model fringe plot to be retained. Keeping up the amount of ‘eye candy’ holds the interest a bit more than the Goodman diagram.
2. The audience can readily assess the factor of safety of the component as you are comparing one number (the EFR stress) to another (the fatigue limit).

I don’t know of many people who use this approach and I would be interested to hear of others who have some experience with it (good and bad).

Numerically the EFR stress = alt/1-(mean/UTS)


I have an Ansys Macro which allows you to plot the EFR on a model. A better explanation may be found here…

http://www.priamengineering.co.uk/efr1.htm

Obviously this only applies to uniaxial loading. I am working on a combined macro which uses EFR in the Miners rule summation.

Regards

Derek Ferguson

http://www.priamengineering.co.uk