Lug G Factor - Coupled Effect of Out of Plane Bending and Local Bore Deformation due to Fastener

[Cevers1988]

It has been a while since my last post, so hello again!

Firstly, Is anyone aware of this empirical factor? Its purpose is augment the inplane stress due to axial loading on either a single or double shear configuration?

The parameters considered are:
- Ratio of male to female lug thickness, e/e'
- Ratio of fastener Stiffness to lug Stiffness, Ef/Ee’
- Ratio of 'studied lug' thickness to fastener diameter, e'/d.

Essentially the question relates to the scope of variables that impact on the two effects captured by this factor. And the most obvious to me is that there should, in my opinion, be an aspect of relative plate stiffness included, Ee/Ee’. Just like in a load transfer calculation, the relative plate stiffness dictates the level of bypass and bearing etc. Hence, the tilt or deformation of the fastener within the studied plate would be directly affected by the level of fixation the adjacent plate provides.

Let me set the scene with regards to the derivation of said factor and it may shed light on what limitations this factor may have due to the scenario in which the data was gathered.

+ All the calculations were created using DFEM results derived from models with congruent materials for male and female… Effectively eliminating this potential effect.
+ Transition fit
+ Loading direction deemed negligible on the effect

What I cannot do is confirm that; given the introduction of material differential the G factor will retain its behavior relative to those given ratios stated above. Without the use of a new DFEM study (which is not a possibility at this point in time).

Along with this caveat, given I am correct, what other conditions may influence this couple of bending and hole distortion?

Kind Regards,

Evo

 

[GrandpaDave]

Evo... You might want to look at the following about the NASA Astonautics Structures Manual.
There is an entire chapter devoted to classical lug hand analysis in Section B. Sorry, I can't help you specifically.
Maybe there's a NASA stress engineer here that can help. The days of good old fashion hand stress analysis are fading away.
G-pa Dave

NASA/TM-X-73305 (VOLUME I), NASA TECHNICAL MEMORANDUM: ASTRONAUTIC STRUCTURES MANUAL (AUG-1975) [SUPERSEDING VOL. I AND II, NASA TM X-60041 and NASA TM X-60042, RESPECTIVELY]., This document (Volumes I, II, and III) presents a compilation of industry-wide methods in aerospace strength analysis that can be carried out by hand, that are general enough in scope to cover most structures encountered, and that are sophisticated enough to give accurate estimates of the actual strength expected. It provides analysis techniques for the elastic and inelastic stress ranges. It serves not only as a catalog of methods not usually available, but also as a reference source for the background of the methods themselves. An overview of the manual is as follows: Section A is a general introduction of methods uses, and includes sections on loads, combined stresses, and interaction curves; Section b is devoted to methods on strength analysis; Section C is devoted to the topic of structural stability; Section D is on thermal stresses; Section E is on fatigue and fracture mechanics; Section F is on composites; Section G is on rotating machinery; and Section H is on statistics. These three volumes supersede NASA TM X-60041 and NASA TM X-60042.

 

[Cevers1988]

G-pa Dave,

Cheers for the NASA reference, unfortunately I didn't stipulate the structural arena; this is a fatigue study, essentially looking into the local effect of a fastener on the bore. This local deformation increases the Kt or stress raiser/intensity factor of the feature. The analysis on Lugs typically found in older resources are limited to static consideration and hence fastener rupture and tear out are the drivers.

I guess a 'fatigue' Huth formula is what I am after which can be applied to the lug.

Cheers,

Evo