STRESS CONCENTRATION FACTOR, SHORT CHAMFER IN EDGE OF CIRCULAR APERTURE 3

[StressMan2506]

Fellow Stress Engineers:

Do any of you know of a reference to a stress concentration factor in-way-of a chamfer over a small proportion of the circumference of a circular aperture; see attached view.

Thanks in anticipation.

StressMan

 

[rb1957]

i doubt there's a solution for such a specific geometry. You might have more luck if you consider just the OD of the CSK as a "bump" on the hole contour. A conservative model would be to consider the large cut-out but use the CSK as the corner radius.

another day in paradise, or is paradise one day closer ?

 

[edmeister]

Obviously this is an upper skin plank; primary structure related to an access hole cut-out. This is no simple fix! If you have the loads - then you have to calculate the critical crack length; and set up a threshold / repeat inspection. Only if the intervals are less than OEM specified detailed wing inspections intervals for that location; will allow removal of this additional special inspection. Never the less - in either case, the inspection interval has to be worked out and submitted to the authorities (Damage Tolerant analysis - DER approval).
- If you do not have the loads or cyclic loading - than this is a good time to get acquainted with the OEM.
- For an added margin of safety - the blended location will have to be NDT crack checked; roto-peened & corrosion-resistance treated.
* Wing plank damage around cut-outs is regarded as significant damage - regardless how small the defect.

 

[GrandpaDave]

Peterson's text on stress concentration factors was, and still is, the bible for stress engineers. There
is a 3rd edition that I don't have since being retired for quite some time.
R. Roark's "Formulas for Stress and Strain" has some tables for concentration factors... not very complete.
G-pa Dave

 

[StressMan2506]

Thanks, guys.

The blend is at a systems penetration in a wing rib. To design, fatigue life is very high. Treating the blend as a chamfer around the entire circumference and calculating an effective plain hole diameter leads to a stress increase at the attachment holes - no problem. I am left however, with what to do at the blend. edmeister's reply indicates that it is not trivial.

StressMan

 

[banag]

I remember the example for stress concentration superposition.
Considering the following case: 1) A hole in a plate 2) A notch at the edge of the hole
Stress concentration for each calculated separately.
1) Hole - Kt of 3
2) Notch - Kt of 2
Stress concentration superposition (assuming the notch is located at peak kt location of the hole - normal to loading direction)
Total kt = Hole kt x notch kt = 3 x 2 = 6 (Stress raises too much!)
For this case, chamfer can be assumed as notch, since chamfer is extended to the most of the thickness.

 

[rb1957]

it's hard (for me) to see that much of the problem from the pic posted. It looks like it's protruding from a larger cut-out. If it's in the corner of this larger cut-out, that's going to be a problem. If there's a lot of shear, travelling around the larger cut-out, that's going to be a problem.

You might get somewhere if you consider the problem similar to a hole with a bump, and assume the Kt increases by the same ratio ... Kt = Kt_cut-out*Kt_circle_with_bump/Kt_circle

another day in paradise, or is paradise one day closer ?

 

[MNLiaison]

The URL below is to a paper that I found a few years ago and thought it may be useful in the MRB / Liaison role. Seems very relevant to your discrepancy.

http://espace.library.uq.edu.au/view/UQ:131820/A1.3.pdf

Regards

 

[StressMan2506]

Special thanks to MNLiaison. The linked paper certainly looks pertinent to my case. Thorough study will tell.

Regards,
StressMan