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272 STRENGTH OF MATERIALS.
TABLE No. 33 Constant c,
The torsional deflection in degrees per foot of length for a
shaft of one inch side or diameter when loaded with one pound
at the end of a lever one foot long
:
Material.
Machinery Steel
Wrought Iron .
Cast-iron ....
Oak ..... .
Ash
Pine and Spruce
Round Square
Section. Section.
0.00914° 0.00538°
0.00914° 0.00538°
0.018° 0.0106°
0.795° 0.468°
0.784° 0.460°
1.35° 0.79°
Example.
A round bar of wrought iron 16 feet long and 3 inches in
diameter is fastened at one end and the other is exposed to a
twisting load of 1000 pounds, acting with 5 feet leverage. How
many degrees will this load deflect the bar ?
Solution
S~-
Sz
16 X 5 X 1000 X 0.00914
34
731.2
81
S- 9 degrees.
Note.—From Table No. 33, it is seen that only steel and
wrought iron are suitable for shafts exposed to torsional stress.
Wrought iron is about twice as good as cast-iron, over 80 times
better than oak, and about 150 times as good as pine.
SHEARING STRENGTH.
Sometimes force may act in such a manner that the
material is sheared off. For instance, the rivets in a steam
boiler are exposed to shearing stress (see Fig. 39) when the
boiler is under steam pressure.
Fig. 39.
When holes are punched or bars of r f? [
iron are cut off under punching presses, ’
,jjZ
]
the action of the punch in cutting off the ~* «* *»» »-
material is shearing, and the resistance which the material offers
is its ultimate shearing strength. The average ultimate shear-
ing strength of wrought iron is 40,000 pounds per square inch.
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