Simple Stress Analysis: Plat Plate with Hole

[Saladsamurai]

Hello All,

I have a fixture that is used for lifting an engine. See attached image for the part in question. You can see in the 'front' view the hole where a pin passes through the part and the lifting lug of the engine. You can also see the loading.

We want to machine the part down such that the .144 dimension goes down to .070. I am just wondering what king of analysis I can do on this? I have a view with the assumed simplified area for analysis. Here is what I am thinking of doing:

1. Shear stress on front face. Do I use only the blue-shaded area? Or do I use the full area with some sort of consideration for the hole? If the latter, do you know where I can learn about such a model?

2. The pin makes contact with the hole along its thickness so I would need to look at the normal stress on the inside of the hole. The surface is cylindrical so I am wondering if there is a common practice for this? If so, where can I see it?


I am going through "Roark's Formulas for Stress and Strain" and "Shigley's" to see what I can come up with, but if someone with some experience could chime in, that would be great. I don't have a lot of support at my company (yet, we're hiring some experience now).

Thank you for your time.

Using NX 7.5.3 & Teamcenter 8

 

[MikeHalloran]

Please do not use "Simple" to describe a problem that you cannot solve.

.070" is typical of the tolerance on engine decking equipment, not the nominal dimension.
Why, pray tell, are you proposing to thin an already flatted shackle ear?







Mike Halloran
Pembroke Pines, FL, USA

 

[Saladsamurai]

Hi Mike,

Do you have any advice to offer? Or just complaints?

It's "simple" in the sense that I am looking to do hand calcs only (if possible), not an in-depth FEA. "Why" we need to thin the part has nothing to do with this post.

If anyone has any constructive advice, that would be great.

Thanks again.


Using NX 7.5.3 & Teamcenter 8

 

[rb1957]

look up "lug shear tear-out" ... you are reducing the strength of the lug. the simple, easy, solution would be to analyze the lug with a reduced OD (of 0.79" ?)

Quando Omni Flunkus Moritati

 

[Saladsamurai]

look up "lug shear tear-out" ... you are reducing the strength of the lug. the simple, easy, solution would be to analyze the lug with a reduced OD (of 0.79" ?)

Hi rb1957: I see, so we would just treat the fixture as a lug itself. Makes sense intuitively, thanks so much, I will start digging.


MikeHalloran: Perhaps I should not have responded the way I did. I should have taken the high road and simply ignored your post. Looking at your profile, you clearly have a lot of knowledge to offer, it's too bad you came off as condescending. Perhaps I misconstrued.

Using NX 7.5.3 & Teamcenter 8

 

[kingnero]

Please do not use "Simple" to describe a problem that you cannot solve.

Why shouldn't he? It is, after all, a rather simple problem.
I do not agree with the geometry changes he proposes, but that doesn't change the underlying problem.

I am not a specialist of USA codes, but I do believe it is all fairly well explained in the "Below The Hook" code.

 

[MikeHalloran]

The problem as presented should be soluble, or estimable, with BTH codes, as noted.

The point that I didn't quite make is that the part is entirely too delicate for my taste, in realizable materials, with undimensioned features proportional to the dimensioned ones in the sketch, even before you start trimming it.

... and the nature of the trim suggests there are severe clearance problems just below the pin, so another point that I didn't quite make is that you need to expand the scope of your investigation and figure out if trimming the lug is indeed the least awful solution to whatever the larger problem might be.

... and IMHO, even if you restrict yourself to just analyzing the part disclosed so far, you can't ethically just cover the case where the load P is downward. You also have to cover the case where at least one of the other engine lift points has failed or otherwise come adrift, so that there is a moment being applied to the extant part, said moment comprising a generally downward force as shown, and a generally upward force where the intended clearance has been taken up by unintended rotation of the engine.

I.e., because you have to trim the lug to clear something, you cannot then assume that the load on the lug is always just a simple radial force, because obviously you can't swing the load (whatever the pin carries) around the pin axis freely without destroying the clearance you want to provide, so you have to cover the case where the clearance goes away. ... or provide the clearance all around any reasonable arc of rotation.

WE don't need to see the rest of the assembly, or the larger scope in which the extant problem resides, but YOU certainly should take a look at it with a very jaundiced eye.

Said as politely and as constructively as I possibly can...



Mike Halloran
Pembroke Pines, FL, USA