Forces and equilibrium - Orthopaedic Biomaterials in Research and Practice - page 21

R T = 1625 N
R C = 625 N

R

Moment (Nm)
50 100

M M
= 40 Nm

1 cm = 500 N
1 cm = 4 cm

FIGUre 1.16 moment diagram for nail-plate fixation device (Problem

1.11).

PROBLEM 1.11
In Figure 1.15, where in the device is the maximum moment experienced?

ANSWER:
In Figure 1.16, a moment diagram is constructed by plotting the perpen-
dicular distance from the line of action of the force to the device times
the magnitude of the force. It can be seen that the maximum moment,
approximately 40 N ∙ m, occurs at the base of the barrel of the nail-plate.
This is the location of the nail-plate junction in one-part devices; most
devices are strengthened in this location to withstand this peak moment.

annotated bibliography

1. ASTM SI10 - 10 IEEE/ASTM SI 10 American National Standard for
Metric Practice, Annual Book of Standards, 2010, Vol. 14.04 , American
Society for Testing and Materials, Conshohocken, 2010.

The standard reference on the SI metric system.

2. Alexander RM: Animal Mechanics . University of Washington,
Seattle, 1968.

Biomechanics of swimming, crawling, running, and flying things.
Chapter 1 has an elegant illustration of free body analysis in the examina-
tion of the mechanics of chewing in several species of fossil reptiles.

3. Dempster WT: Free body diagrams as an approach to the mechanics of
human posture and motion. In Evans FG (ed): Biomechanical Studies of
the Musculo-Skeletal System . Charles C Thomas, Springfield, IL, 1961.