Question

Repeat Example Problem 4.9 using a cobalt alloy rod with circular cross-sectional diameter of 10 mm.

EXAMPLE PROBLEM 4.9 Figure 4.16 (left) shows an orthopedic nail-plate used to fix an intertrochanteric fracture. The hip applies an external force of 400 N during static standing, as shown. The nail-plate is rectangular stainless steel with cross-sectional dimensions of 10 mm (width) by 5 mm (height), and is well-fixed with screws along its vertical axis and friction fit into the trochanteric head (along the x-axis). What forces, moments, stresses, and strains will develop in this orthopedic device? Solution As for any statics problem, the first task is constructing a free-body diagram, including all applied forces and moments and all reaction forces and moments that develop at the supports. Because of the instability at the fracture site, the nail-plate may be required to carry the entire 400 N load. Consequently, one reasonable model of the nail-plate is a cantilever beam of length 0.06 m with a combined loading, as depicted in Figure 4.16 (right, top). The applied 400 N load consists of both axial and transverse components: F1 = 400 N cos 20° = 376 N Fy = 400 N sin 20° = 137 N 400 N 20 0.06m 135" M. 376N 8.22 Nm FIGURE 4.16 (Left) An intertrochanteric nail plate used in bone repair. To the right is the free-body diagram of the upper section of this device, and below it is the free-body diagram of a section of this beam cut at a distance x from the left-hand support. Adapted from [21

Answer 1

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