A beam element has the same material composition throughout and therefore the same mechanical properties at every position in the material. Therefore, the modulus of elasticity E is constant throughout the beam element. A member in which the material properties varies from one point to the next in the member is called inhomogenous (non-homogenous). If a beam is composed of different types of materials, then it must be divide up into elements that are each of a single homogeneous material, otherwise the solution will not be exact.
The left figure shows a composite beam composed of brass and aluminum. This structure can be divided into two elements as shown on the right, one element for the brass with E1 = 15 x 106 psi and one for the aluminum with E2 = 10 x 106 psi.