For convenience in working the following problems we will use values given in the table below, unless otherwise specified. These are average values which have been established by actual test.

Material

E.L.

U.T.S.

U.E.

U.S.S.

U.C.S.

Brick.........

2,000

Stone..........

6,000

Timber.........

3,000

10,000

.015

3,000

8,000

Cast Iron.......

6,000

20,000

.005

20,000

90,000

Wrought Iron...

25,000

55,000

.20

50,000

55,000

Steel...........

50,000

100,000

.10

70,000

150,000

E.L.

=

Elastic limit

U.T.S.

=

Ultimate tensile strength

U.E.

=

Ultimate elongation

U.S.S

=

Ultimate shearing strength

U.C.S..

=

Ultimate compressive strength

The above is given in pounds per square inch, except "ultimate elongation" which is given in inches per linear inch, "linear" meaning "inch of length."

1. A piece of steel shows a tensile strength of 85,000 lbs. per square inch, and is used in a bridge where it is subjected to a steady stress of 17,000 lbs. per square inch. What is the factor of safety?

2. If a piece of wrought iron has a tensile strength of 42,000 lbs. per square inch, find the load that would be needed to break, in the testing machine, a piece of the same material 3/4 in. in diameter.

3. A wrought iron bar 3/8 in. in diameter is pulled apart at a load of 4970 lbs. What would be the tensile strength of this iron?

4. What would be a safe load for the bar in problem 3 if it were to be subjected to a varying stress?

5. A piece of steel plate with a cross-section 1/2 in. X 1 in. pulled apart in the testing machine requires a load of 29,600 lbs. What load would a piece with 1 in. cross-section require?

6. A piece of steel 1/4 in. square pulled apart in the testing machine requires a load of 6000 lbs. What is the ultimate tensile strength of this material?

7. There are four wrought iron bolts in the press shown in Fig. 106. If the capacity of the press is 10,000 lbs., what size should the bolts be?

8. What must be the diameter of a steel piston rod if the piston is 18 in. in diameter and the steam pressure is 110 lbs. per square inch?

Area of piston = 182 X .7854 = 254.47

254.47 X 110 = 27,991.7 lbs. or, about 28,000 lbs., which is the stress in the rod.

9. What size piston rod must we use if the piston is 22 in. in diameter and the steam pressure is 150 lbs.?

Fig. 106.   Letter Press.

Fig. 106. - Letter Press.