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STRENGTH OF MATERIALS. 217
Example.
A piece of iron y
2 inch square is tested in a testing machine
and breaks at a total stress of 14,210 pounds. What is the
ultimate tensile strength per square inch ?
Solution
:
A bar y
2 inch square has a cross-sectional area of yX x
/
2
"
is X square inch.
14^10
S = = 56,840 pounds per square inch.
X
Example.
What will be the breaking load for a wrought iron bar
H" X }i" when exposed to tensile stress, the ultimate tensile
strength of the iron being 55,000 pounds per square inch, as
given in Table No. 25, page 216 ?
Solution
:
A bar y&" X }i" is g
9
T square inches in area.
P = fa X 55,000 = 7734 pounds, which will break the bar.
In order to obtain the safe working stress introduce a suit-
able factor of safety, from 5 to 10, according to circumstances,
and calculate by the following formulas
:
a y, c Side of a square bar = -\i —_/
/
a — P X f Diameter of a round bar == \ *^—
A
s~ ^0.7854 S
P = Load in pounds.
/ = Factor of safety.
Example.
A load of 24,000 pounds is suspended on a round wrought
iron bar. The ultimate tensile strength of the iron is 55,000
pounds per square inch. What should be the diameter of the
bar to sustain the load, with 10 as the factor of safety ?
Solution:
A
s
-
A = ?4000_X10 = 4.363 square inches.
55000
In Table No. 24, we find the nearest larger diameter to be
’2yi inches.
The diameter may also be calculated directly by the fol-
lowing formula
:
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