Problem 2.1 The composite bar shown in Fig. 1-20(a) is rigidly attached to the two supports. The left portion of the bar is copper, of uniform cross-sectional area 80 cm² and length 30 cm. The right portion is aluminum, of uniform cross-sectional area 20 cm² and length 20 cm At a temperature of 26°C the entire assembly is stress free. The temperature of the structure drops and during this process the right support yields 0.025 mm in the direction of the contracting metal. Determine the minimum temperature to which the assembly may be subjected in order that the stress in the aluminum does not exceed 160 MPa. For copper E = 100 GPa, α = 17 × 10-6/°C, and for aluminum E = 80 GPa, a = 23 × 10-6/°C. -30 cm- (a) +20 cm- Fig 1-20