Choose a Boundary Condition and Calculate! 


Constitutive 
The constitutive equation describes how the direct stress s and direct strain e within the beam are related.
Direct means perpendicular to a beam cross section; if we were to cut the beam at a given location, we would find a distribution of direct stress acting on the beam face,
Beam theory typically uses the simple 1dimensional Hooke's Equation,
Note that the stress and strain are functions of the entire beam cross section (i.e. they can vary with y). 