고체역학 (Gere) — Stresses in Beams (Advanced Topics): Problem 6.2-9

6.2-9 The cross section of a sandwich beam consisting of aluminum alloy faces and a foam core is shown in the figure. The width $b$ of the beam is 200 mm, the thickness $t$ of the faces is 6 mm, and the height $h_c$ of the core is 140 mm (total height $h = 152\text{ mm}$). The moduli of elasticity are 70 GPa for the aluminum faces and 80 MPa for the foam core. A bending moment $M = 4.5\text{ kN}\cdot\text{m}$ acts about the $z$ axis. Determine the maximum stresses in the faces and the core using (a) the general theory for composite beams and (b) the approximate theory for sandwich beams.