1) A number 10 (No. 10) steel rebar is tested in tension. By monitoring the load reading of the testing machine, it was found that the specimen yielded at a load of 41,600 lb and fractured at 48,300 lb.
a. Determine the tensile stresses at yield and at fracture.
b. Estimate how much increase in length would occur at 70% of the yield stress in a 2-in gauge length.
2) A grade 36 round steel bar with a diameter of 0.5 inches and a gauge length of 2 inches was subjected to tension to rupture following ASTM E-8 test procedure. The load and deformation data were as shown in the following table:
|
Load (kips)
|
Displacement (in.)
|
Load (kips)
|
Displacement (in.)
|
|
0
|
0
|
8.56
|
0.08301
|
|
2.75
|
0.00096
|
8.79
|
0.03557
|
|
4.07
|
0.00141
|
8.98
|
0.10878
|
|
7.12
|
0.00252
|
9.15
|
0.12207
|
|
7.14
|
0.01691
|
9.25
|
0.13372
|
|
7.34
|
0.04196
|
9.35
|
0.14741
|
|
7.53
|
0.04599
|
9.44
|
0.18199
|
|
7.91
|
0.5847
|
7.87
|
0.29814
|
|
8.28
|
0.07117
|
|
|
Using a spreadsheet program obtain the following:
a. A plot of the stress-strain relationship. Label the axes and show units.
b. A plot of the linear portion of the stress-strain relationship. Determine modulus of elasticity using the best fit approach.
c. Proportional limit.
d. Yield stress.
e. Ultimate strength.
f. When the applied load was 4.07 kips, the diameter was measured as 0.499905 inches. Determine Poisson's ratio.
g. After the rod was broken, the two parts were put together and the diameter at the neck was measured as 0.416012 inches. What is the true stress value at fracture? Is the true stress at fracture larger or smaller than the engineering stress at fracture? Why?
h. Do you expect the true strain at fracture to be larger or smaller than the engineering strain at fracture? Why?
3) A Charpy V Notch test was conducted for an ASTM A572 Grade 50 bridge steel. The average values of the test results at four different test temperatures were found to be:
10 ft.lb at -50°F
15 ft.lb at 0°F
40 ft.lb at 40°F
60 ft.lb at 100°F
The bridge will be located in a region where specifications require a minimum of 25 ft.lb fracture toughness at 30°F for welded fracture-critical members. If the bridge contains a welded flange in a fracture-critical member, does the steel have adequate Charpy V notch fracture toughness? Show your supporting calculations.
4) Discuss the main methods used to protect steel from corrosion.