Design Ideas for a "Fused" Solution 2

[Adz123]

Hi guys,

I am currently working on a development project and I am looking for some ideas for a "fused" solution, see attached image.

In simple theoretical form, the design utilizes 2 beams that are attached together, see attached image.

Beam 1 is fixed on one end. beam 2 is fixed to beam 1, the method of attachment is currently TBD depending on the fuse solution.

2 different overload cases are considered, namely:
Load A acting in the vertical direction at the most outer edge of beam 2.
Load B acting horizontally, again at the most outer edge of beam 2.
The 2 loads ae acting independently and separately (i.e. not simultaneously)

The requirement is to design a "fused" solution that prevents the overloading on beam 2 (load A or B) from being reacted by Beam 1. This will be accomplished by demonstrating that the margin of safety is the lowest at the fused location, so that when X load is applied in the directions of Load A or B, beam 2 should fully detach at the fused location, and not just yield/bend (and this is the challenge).

The single fuse point should work for both load cases and should be as close to the beam1-beam2 attachment a possible.

Any ideas?

 

[MintJulep]

Loads A and B applied separately or at the same time?

 

[MintJulep]

Ok, here's my solution.

Vary L and d to get what you need to match your loads A and B.

 

[Adz123]

Loads A and B applied separately or at the same time?

Thank you for the idea. Loads A & B are applied separately.

As for your proposed solution, can you clarify what the following is?

Also, how many fuse bolts are you proposing to attached the two beams together? As a minimum 2 are needed to prevent rotation, and Ideally 4 as best practice, however how can we guarantee that all fuse bolts will fail simultaneously rather than some shearing and some bending? I cant see how the failure mode will only be shear.

 

[MintJulep]

It's a ball bearing retained in comical holes in both plates.

It allows:
Plates to yaw in response to load A.
Plates to pitch in response to load B.

With that, you only need one bolt, avoiding the simultaneous failure problem

Failure mode for load A is shear.

Failure mode for load B is tension (and a bit of bending maybe).

 

[3DDave]

MJ - nice solution.

 

[rb1957]

why not just shear the (4) bolts at some design load ... the load you'll permit into the supporting structure ?

or a stress concentration notch.

How far apart are the typical service loads and this defined failure load ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[SWComposites]

how can we guarantee that all fuse bolts will fail simultaneously rather than some shearing and some bending? I cant see how the failure mode will only be shear. you need to carefully design the notch in the fasteners to ensure a shear failure mode. and if you want a precise failure load, you need to make and test the special notched bolts for each batch of fasteners and adjust the notch machining to dial in the required shear failure load.

 

[rb1957]

looking at MJ's very creative solution ... the ball bearing is in compression, but is on the compression side of the reaction. What if we flipped it 180 degrees, so that the ball bearing is in compression as the bolt is tightened, then the applied load tries to unload this compression and eventually the joint would lose moment capability (it'd fall to "heel and toe" prying and then to nothing.

"Of course" we don't need a ball bearing ... if we had a step so something could contact the support beam first as the bolt is tightened. You could add a spring on the bolt to tighten against.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[BrianE22]

MJ's proposal looks nice - I only question the amount of preload you can get on the bolt.

 

[MintJulep]

To clarify a bit.

L[sub]A[/sub] controls the response to Load A
L[sub]B[/sub] controls the response to Load