Chapter 3, Problem 42P

For the knuckle joint described in Prob. 3-40, assume the maximum allowable tensile stress in the pin is 30 kpsi and the maximum allowable shearing stress in the pin is 15 kpsi. Use the model shown in part c of the figure to determine a minimum pin diameter for each of the following potential failure modes.

1. (a)   Consider failure based on bending at the point of maximum bending stress in the pin.
2. (b)   Consider failure based on the average shear stress on the pin cross section at the interface plane of the knuckle and clevis.
3. (c)   Consider failure based on shear at the point of the maximum transverse shear stress in the pin.

3-40* A pin in a knuckle joint canning a tensile load F deflects somewhat on account of this loading, making the distribution of reaction and load as shown in part (b) of the figure. A common simplification is to assume uniform load distributions, as shown in part (c). To further simplify, designers may consider replacing the distributed loads with point loads, such as in the two models shown in parts d and e. If a = 0.5 in. b = 0.75 in. d = 0.5 in. and F = 1000 lbf, estimate the maximum bending stress and the maximum shear stress due to V for the three simplified models. Compare the three models from a designer's perspective in terms of accuracy, safely, and modeling time.

Problem 3-40*