Civil Engineering Reference
In-Depth Information
test specimen should be sound, without imperfections near the surface.
Also, the specimen should be straight and of uniform diameter for a length
equal to the gauge length plus two to four diameters. The gauge length
should be at least four diameters. During the test, torque is read from a dial
gauge or a readout device attached to the testing machine, while the angle of
twist may be measured using a torsiometer fastened to the specimen at the
two ends of the gauge length. A curve-fitting procedure can be used to esti-
mate the straight-line portion of the shear stress-strain relation of Figure
3.17 (ASTM E143).
Sample Problem 3.4
A rod with a length of 1 m and a radius of 20 mm is made of high-strength steel. The rod
is subjected to a torque
T,
which produces a shear stress below the proportional limit. If
the cross section at one end is rotated 45 degrees in relation to the other end, and the
shear modulus
G
of the material is 90 GPa, what is the amount of applied torque?
Solution
J
= p
r
4
/2
4
/2
10
-
6
m
4
= p
1
0.02
2
=
0.2513
*
u
=
45
1
p
/180
2
= p
/4
10
9
10
-
6
T
=
GJ
u
/
L
=
1
90
*
2
*
1
0.2513
*
2
*
1
p
/4
2
/1
10
3
N.m
=
17.8
*
=
17.8 kN.m
■
3.8.3
Charpy V Notch Impact Test
The Charpy V Notch impact test (ASTM E23) is used to measure the tough-
ness of the material or the energy required to fracture a V-notched simply sup-
ported specimen. The test is used for structural steels in tension members.
The standard specimen is
with a V notch at the center, as shown in Figure 3.18. Before testing, the
specimen is brought to the specified temperature for a minimum of 5 min in
a liquid bath or 30 min in a gas medium. The specimen is inserted into the
Charpy V notch impact-testing machine (Figure 3.19) using centering tongs.
The swinging arm of the machine has a striking tip that impacts the speci-
men on the side opposite the V notch. The striking head is released from
the pretest position, striking and fracturing the specimen. By fracturing
the test specimen, some of the kinetic energy of the striking head is ab-
sorbed, thereby reducing the ultimate height the strike head attains. By
measuring the height the strike head attains after striking the specimen,
55
*
10
*
10 mm
1
2.165
*
0.394
*
0.394 in.
2
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