Composite beam flexural modulus

[Rhodes]

If I have a composite beam or an T beam where the top of the T is of significantly higher stiffness than the vertical part.

is it true that the further a stiffness material is from the neutral axis the greater the effect on the overall stiffness is? is it possible to calculate a new flexural modulus, that takes into account for this increased stiffness material the further it gets from the Neutral axis?

 

[SteamKing]

Take a look at this article about analyzing bending of "composite beams":

http://www.roymech.co.uk/Useful_Tables/Beams/Beam_theory.html

The stuff you're interested in is at the bottom, but the first part is a good reference, too.

 

[Rhodes]

Thanks however I have seen this and the problem is it calculates the stress at the two faces under compression and tension.

I am hoping for a comparison for flexural modulus.

probably impossible because I am trying to place a dimension to a dimensionless property.
unless there is a way and I am wrong in which i would be very grateful

 

[Chestermiller]

You want to know how to determine the flexural stiffness of a composite beam. SteamKing's article has it, if you study the article some more. The trick is to assume that the axial strain is a linear function of position through the thickness of the beam. If you specify a radius of curvature, then you know the slope, but not the depth at which the strain is zero. You treat that as an unknown, and integrate to get the axial force on the beam (taking into account that the modulus changes from material to material through the depth). Assuming that you are only applying a moment to the beam, the axial force has to be zero. This tells you the depth at which the strain is zero. You then integrate to get the bending moment. Once you know the bending moment and the radius of curvature, you know the flexural stiffness.

Chet