申論題

2.(30分) A trimetallic bar is uniformly compressed by an axial force P = 12 kN applied through a rigid end plate (see figure). The bar consists of a circular steel core surrounded by brass and copper tubes. The steel core has diameter 10 mm, the brass tube has outer diameter 15 mm, and the copper tube has outer diameter 20 mm. The moduli of elasticity for steel, brass and copper are 210, 100, and 120 GPa, respectively.