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STRENGTH OF MATERIALS. 273
In cast-iron the ultimate shearing strength is usually between
20,000 and 30,000 pounds per square inch. In steel the ultimate
shearing strength will vary from 40,000 to 80,000 pounds per
square inch.
The resistance offered to shearing is in proportion to
the sheared area. Thus, it will take twice as much force
to punch a hole two inches in diameter through a three-eighths
inch plate as it would to punch a hole only one inch in diameter
through the same plate, and it will take four times as much
force to shear off a one-inch bolt as it would to shear off a one-
half inch bolt, because the area of a one-inch bolt is four times
as large as the area of a one-half inch bolt.
Example 1.
How much force is required to shear off a wrought iron
rivet of one-inch diameter if the shearing strength of the
wrought iron is 40,000 pounds.
Solution :
One-inch diameter = 0.7854 square inches; therefore the
force required will be 0.7854 X 40,000 = 31,416 pounds.
Example 2.
A wrought iron plate is one-quarter of an inch thick and
the ultimate shearing strength of the iron is 40,000 pounds per
square inch. How much pressure is required to punch a hole
three-quarters of an inch in diameter ?
Solution
:
The circumference of a %-inch circle is 2.356 inches. The
plate is X-inch thick; therefore the area of shearing surface,
2.3562 X X = 0.58905 ; thus, the force required will be 40,000
X 0.58905 = 23,562 pounds.
TABLE No. 34.—Shearing Strength Per Square Inch.
Material.
Steel
Wrought Iron Rivets
Cast-iron . . . .
•
Oak, crosswise . . .
Oak, lengthwise . .
Pitch Pine, crosswise
Pitch Pine, lengthwise
Spruce, crosswise . .
Spruce, lengthwise .
Pounds Per Square Inch.
45,000 to 75,000
35,000 to 55,000
20,000 to 30.000
4,500 to 5,500
400 to 700
4,000 to 5,000
400 to 600
3,000 to 4,000
300 to 500
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