Single shear joint fastener flexibility comparison to FEM

[BragiBaldursson]

Can an FEA expert with access to Abaqus/Nastran see if they can match this simple problem of a single shear joint with riveted fasteners. Fasteners are to be modeled as beam elements (circular) tied to the doubler and skin (1 inch apart). Fastener diameter is calculated from Tom Swift´s fastener flexibility to be 0.406 inches in diameter and fastener length of 1 inch. I would like to know if the hand calculations compare well with FEM results for the bearing and bypass loads.

 

[BragiBaldursson]

You missed the point rb1957. The excercise was all about using a fastener length of 1 inch.

 

[rb1957]

well, yeah, I missed that point. I thought you were trying to solve a real problem. As shown in your first pic, the three vertical arrows (which look like axial load on the fasteners) should be horizontal, as these are shear loads in the fasteners.

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

 

[BragiBaldursson]

rb1957 still a real problem to determine bearing and bypass loads

 

[rb1957]

not with 1" long fasteners. fastener length should be (AFAIK, AFAIC, IMHO, IMAO) (tsk+tdblr)/2. By using 1" long fasteners you're using an artificially high shear stiffness, to capture the behaviour of much shorter fasteners. The real problem is easily solved with a compliance model, which is equally easily transferred into the FEM world (oh, but then that's the point of the post ... you're starting with fastener shear compliance, based on the Boeing stiffness calc [1]). You're modelling a 3/16" rivet that is joining two sheets, 0.05" and 0.04" thk, as a beam 0.406" diameter and 1" long ... and this makes sense ? what kills the problem solution is the increased offset between the load and the reaction (what should be 0.045" is now 1") ... this is not good modelling. I'm not sure what you're learning (or supposed to learn) from this.


[1] an interesting take away is how different are the formulations for fastener stiffness (compare Boeing, Douglas, Huth)

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

 

[BragiBaldursson]

Rb1957 explain to me in detail how you would setup a finite element model to model this? I actually like this approach because it makes it very visual especially if you have several straps. The offset between applied load and the reaction is the same as I have adjusted the diameter of the fastener as well to be artificially big and hence you get correct results as expected.

 

[Ng2020]

Bragi, nobody uses this method.
You could try (nastran) celas elements if you want to visualise the individual straps.
See also eng tips thread825-358723

 

[LiftDivergence]

I'm also confused by the direction this thread is going...

which is equally easily transferred into the FEM world (oh, but then that's the point of the post ... you're starting with fastener shear compliance, based on the Boeing stiffness calc [1]). You're modelling a 3/16" rivet that is joining two sheets, 0.05" and 0.04" thk, as a beam 0.406" diameter and 1" long ... and this makes sense ? what kills the problem solution is the increased offset between the load and the reaction (what should be 0.045" is now 1") ... this is not good modelling.

Rb1957 explain to me in detail how you would setup a finite element model to model this?

From the start it seemed like the question was not regarding the 1D load transfer analysis itself. OP stated they had that worked out but either didn't trust the results or just wanted to verify them using FEA. Problem is OP doesn't have access to FEA software and was asking someone in the forums to do it for them instead.

I said:
1. This has been studied extensively and there are probably a plethora of papers doing that exact type of verification
2. You don't need software necessarily to do simple FEA.
3. Myself and others pointed out the questionable usefulness of this effort since 2D plates width actual width will not perfectly approximate the 1D compliance model results, and also secondary bending due to eccentricity needs to be accounted for.

OP basically cast some insults and now the discussion has shifted to:
-people giving advice on how to perform 1D compliance model calculations (not the question at hand)
-discussion of specific FE modelling practices, even though OP has stated they don't have access to any software.

Overall there is a lack of clear communication in what we're looking for. So OP, are you still looking for someone to create a FEM for you, or are you simply looking for any software which will automate your hand calcs? Because that is not the same as validating. If you are using the tool ESPcomposites linked to, that is not a verification, it will be using the same method you've already done by hand.

Keep em' Flying
//Fight Corrosion!

 

[BragiBaldursson]

This is getting to be quite the exciting post. If you read my original post I was working a problem from a Boeing 777 structures course by hand and I wanted to know how it compared with FEM as the course suggests and the modeling it suggests. That was the question and that is all. I have since then found a suitable FEM software to work it as suggested and got the result I was hoping to get. My hopes from the community was to get details out of it how you model in FEM. Ng2020 offered up using Mystran and bush elements in a 1D problem, which is another alternative. I wanted to know how state of the art modelers model a problem like this with the little details and explain it to the community.

 

[ESPcomposites]

Oh, I forgot, 1D Elements can handle this problem as well (

https://www.structuralfea.com/1D_Elements/1D_Elements.html

). It uses MYSTRAN and I attached an example.

Brian

http://www.espcomposites.com

 

[BragiBaldursson]

Problem solved see

https://www.eng-tips.com/viewthread.cfm?qid=490812

Either method can be used actual 1 inch beams of large diameter or springs.

 

[Stress_Eng]

Just to let you know (FYI), I’ve got a calculation template using the compliance model. I know the method as strain matching. Using the information provided (with the swift equation), I obtain the following fastener loads, 300.6 lbf, 189.5 lbf and 259.9 lbf.

 

[rb1957]

there's one (a compliance model) in Niu. It's simple to set up in excel.

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

 

[rb1957]

and please don't post your email ... at least not without disguising it I think you should edit that post.

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