Aluminum plate welded to aluminum plate section modulus 1

[Sean99]

If two plates of Aluminum (both are 2" tall, and 1/2" thick) were placed over each other (see photo 1) and then welded together all around the perimeter of the second plate (the blue one) as indicated by the yellow lines in photo 2, then would the moment of inertia be calculated as if the local section (only where they are connected) was 2" by 1"? And would the same apply if the second plate was bolted to the first plate using many bolts?

second moment of area/moment of inertia = "I" in the bending stress formula sigma = My/I

 

[SWComposites]

First, this has nothing to do with composite materials.
For first question, Yes.
For second question, Maybe, depending on number and placement of bolts, and their torque level, and the loading level at which “I” is used, and the type of analysis performed, and what this structure is, etc, etc.

 

[Sean99]

Thanks for your response. Can you tell how it is you know the answer to the first question is true? Some kind of proof? I want to know the why of it.

 

[Sean99]

Actually wait! I have one more question. What if you didn't weld directly around the perimeter, but instead welded a perimeter smaller than the total height and width of the second plate like in this new photo attached? You wouldn't be able to then consider it as one piece then right?

 

[SWComposites]

Proof? Basically do the two sections deform together or not.

And I don’t understand at all your second figure.

What real problem are you trying to solve?

 

[Sean99]

You're right, I keep reading that in various place, if two pieces of the same material deform together then they're basically the same piece.

I'm looking into the beam analysis of a tailsitter with two motors, could you take a look at my other post that relates to this? It would be a huge help.

https://www.eng-tips.com/viewthread.cfm?qid=503038

 

[Ng2020]

Hi Sean99. See if you can find a short introductory/intermediate level course on solid mechanics. It will give you the background to answer both this question and the beam internal loads question.