Prob. 2.9-10. At room temperature (70°F) and with no axial load (P = 0) the extensional strain of the prismatic bar (Fig. P2.9-10) in the axial direction is zero, that is,

x = 0. Subsequently, the bar is heated to 120°F and a tensile load P is applied. The material properties for the bar are: E = 10 x 10³ ksi and a = 13 x 10-6/°F, and the cross-sectional area of the bar is 1.8 in². For the latter load-temperature condi- tion, the extensional strain is found to be ex = 900 × 10¯6 in.. (a) Determine the value of the axial tensile load P. (b) De- termine the normal stress and the shear stress on the oblique plane NN'. (Note: The total strain is the sum of strain asso- ciated with normal stress o, (Eq. 2.14) and the strain due to change of temperature AT (Eq. 2.8).) Gage measures extensional strain €x N N' 25° P2.9-10 P ·x