my question is regarding calculation of deflection of a composite beam, ie a beam with a cross section made up of 2 separate homogeneous materials. the methods i know for calculating deflections in homogenous beams are energy methods(catiglianos 2nd) and the elatic curve equations(second integral of the bending moment) my problem is that in both of these methods(and any other method) i need to use E and I, my question is what E and what I should i use here? originally i thought i could move over to an equivalen x-section as i would do co calculate stress from bending, expanding one material and then use the E of the other mateerial. something just doesnt seem right doing that,, (if i used the opposite i would get totally different answers) please help, agaain the question is mainly about which E and I to use.
I guess you'll have to determine where the neutral axis or centroid is in the cross section, this will be skewed towards the material with the higher young's modulus. then to determine I, you can determine I for each of the parts of the cross section then use the parallel axis theorem to determine their moment of inertia about the centroid and add them up like any composite material.