Equivalent sandwich thickness

[kribri]

Hi,
I'm trying to calculate the equivalent thicknesses of the elements in a composite sandwich compared to a steel plate with steel stiffeners (three types of stiffener: flatbar, tbar and angle)

How do I do this?

Krish

 

[msquared48]

What for? Shear? Bending? Deflection?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[kribri]

Sorry, forgot to write that.
I need to compare the bending stiffness (flexural rigidity).

 

[desertfox]

Hi kribri

You need to work the "I" value out for each built up section using the parallel axis theorem have a look at this site, (you might have to scroll down a bit)

http://www.emu.edu.tr/mugp101/PHYS106/architecture/461_lectures/461_lecture28/461_lecture28.html

desertfox

 

[kribri]

desertfox: sorry for causing all this trouble with the double posting.

I have looked at the approach of using a Uneven I-beam (

http://www.efunda.com/designstandards/beams/UnevenIbeam.cfm).

If you can I would we very greatful if you could take a quick look at the calculation in the excel sheet?

kind regards
Kristoffer

 

[desertfox]

Hi kribri

What is the figure to the right of the uneven I beam.
I'll have a look and come back later.

desertfox

 

[kribri]

The figure to the right is a composite sandwich plate. Steel-polyurethan-steel.

I am very greatful for you help.

Krish

 

[desertfox]

Hi kribri

If the uneven "I" beam is all steel then Your spread sheet for the figure on the left is ok.
You only need the "I" value for the beam which you have worked out, at that stage you don't need to multiply by E unless your going to work out the deflection.
The figure on the right I cannot clarify because I am not sure what you have done, however if you have two different materials sandwich together the first thing you need to do is convert one of the materials into the equivalent of the other ie steel-plastic-steel you need to convert the plastic to the equivalent steel section or vice versa.

http://www.freestudy.co.uk/c105/t6.pdf

The link should provide how to do the above you need to scroll to page 11

desertfox

 

[msquared48]

Same idea as converting steel to concrete or vice versa using the "n" value.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[cntw1953]

msquared48 is correct, using transform method to obtain an equivalent section is the first step. Then you would need to verify there is adequate bond strength in between layers to validate the section acts as a composite. From there, you can check stresses and deflections using beam theory.

 

[EdR]

But remember that when using the transformed section method you never change the section depth....only the section width...

If you change the depth then the bending assumptions used in developing the transformed section do not apply.....

The reason I make this caution is that the question was about determining equivalent "thicknesses" which I take to mean the section depth.......

Ed.R.

 

[desertfox]

Hi EdR

Thats a fair point however if he follows the link I posted he won't make that mistake.

desertfox

 

[kribri]

Thank you for all the response. This helps a newbie alot.

To explain: I'm comparing a SPS panel with a stiffened steel panel. What I want to find out is what thicknesses for the steel-faces and the polymer-core can be used for the SPS panel to get equivalent flexural rigidity as the stiffened steel panel.

I see now I probably should have written this in the first post. Sorry for this.