Strength verification for surface hardened components acc. FKM guideline

[dh21]

Has anyone experience in performing strength verifications (static as well as fatigue) for surface hardened components acc. FKM guideline or similar guidelines?

Let's say we have a notch, which is loaded in a pure compressive state acc. FKM chapter 5.3.3 the surface hardened component (surface as well as core below surface layer) are to be evaluated acc. The maximum principle stress theory with sigma 1 (tension). This would mean, that in a case with purely compressive principle stresses (even sigma 1 negative) no verification can be performerd acc. guideline or has not to be performed acc. The guideline respectively as compressive stresses might not be relevant for brittle materials/areas/surfaces.

Can anyone confirm this or has a different approach to perform a strength verification in this case?

 

[dcascap]

FKM 5.3.3 is only for fatigue right? I would say that you can check statically for compressive failure (which would be unlucky to occur but it could).
With respect to fatigue, compressive cycles don't really have an effect on it as you cannot open/grow cracks with it...

 

[mfgenggear]

Hertz hardness is verified for ball bearings and aerospace gears. There tons of white papers on the subject. Not if this is applicable to op questions.

 

[drawoh]

Has anyone experience in performing strength verifications (static as well as fatigue) for surface hardened components acc. FKM guideline or similar guidelines?

Let's say we have a notch, which is loaded in a pure compressive state acc. FKM chapter 5.3.3 the surface hardened component (surface as well as core below surface layer) are to be evaluated acc. The maximum principle stress theory with sigma 1 (tension). This would mean, that in a case with purely compressive principle stresses (even sigma 1 negative) no verification can be performerd acc. guideline or has not to be performed acc. The guideline respectively as compressive stresses might not be relevant for brittle materials/areas/surfaces.

Can anyone confirm this or has a different approach to perform a strength verification in this case?

Are you verifying your design, or inspecting parts?

 

[dh21]

Are you verifying your design, or inspecting parts?

I do want to perform a static as well as a fatigue strength verification for a surface hardened component.

Even though I do think it is conclusive, that compressive cycles are not damaging, I mean we do take these into account in every other basic strength verification where it is necessary to determine the occurring stress amplitudes.

In the FKM guideline it literally says that the maximum principle stress theory is to be used considering the maximum sigma_1_amplitude and sigma_1_mean.
But how could this be interpreted?

A)
sigma_a = The maximum of (Sigma_1_t=2 - Sigma_1_t=1) and (sigma_3_t=2 - sigma_3_t=1)?
Thus, considering the maximum principal stress in terms of values.

B)
assuming |sigma3_t=2| > |sigma1_t=2| && |sigma1_t=1| > |sigma_3_t=1| --> sigma_a = sigma_3_t=2 - sigma_1_t=1?
Thus, considering the total stress amplitude like in every other standard verification

C)
Only considering the positive component of the sigma_1's?
--> sigma_a = sigma_1_t=2 - sigma_1_t=1 (with sigma_1_t=x = 0, if it is < 0)

Hopefully you guys can understand what I am trying to depcit.

It would surely help, if anyone already ever performed a strength verification according FKM guidline chapter 5.5