3. A simply supported composite beam (L = 4.5 m) is subjected to a positive bending moment (680 N-m) at both ends. The beam is made of two materials in a square cross-section. Material 1 is 50x50mm and is surrounded by a 25 mm shell of material 2. Solve for the maximum stress in each material. E1 = 100 GPa, E2 200 GPa. (10 pts)

Fig: 1