Problem 4A titanium [E = 16,500 ksi;  = 5.3×10–6/°F] bar (1) and a bronze [E = 15,200 ksi;  = 12.2×10–6/°F] bar (2), each restrained at one end, are fastened at their free ends by a pin of diameter d = 0.4375 in. The length of bar (1) is L1 = 19 in. and its cross-sectional area is A1 = 0.50 in.2. The length of bar (2) is L2 = 27 in. and its cross-sectional area is A2 = 0.65 in.2. What is the average shear stress in the pin at B if the temperature changes by 40°F?

Respuesta :

Answer:

[tex]\tau_a = 22.7 ksi[/tex]

Explanation:

Given data:

[tex]\alpha  = 12.2 \times 10^{-6} [/tex]degree F

Diameter is d = 0.4375

[tex]L_1 = 19 inch[/tex]

[tex]A_1 = 0.50 in^2[/tex]

[tex]L_2 = 27 inch[/tex]

[tex]A_2 = 0.65 in^2[/tex]

force in titanium and bronze will be equal

from equilibrium condition we have

F_T = F_B = p

From the information given as bar is tightened from ends thus net deformation is assummed to be zero

so we have

[tex]\Delta_T +\Delta_B = \Delta  = 0[/tex]

[tex]\frac{PL}{AE}_T + \alpha \Delta T L = \frac{PL}{AE}_B + (\alpha \Delta T L)_B[/tex]

[tex]\frac{19\times P}{0.5\times 16500} + 19 \times 5.3\times 10^{-6} \times 40 = \frac{27P}{0.65 \times 15200} + 27\times 12.2\times 10^{-6} \times 40 = 0 [/tex]

solving for P we get

P = 341 kips

average shear at B

[tex]\tau_a = \frac{P}{A}[/tex]

[tex]\tau_a = \frac{341}{\frac{\pi}{4} \times 0.4375^2}[/tex]

[tex]\tau_a = 22.7 ksi[/tex]