Page 165 - Mechanical Behavior of Materials

166 Chapter 4 Mechanical Testing: Tension Test and Other Basic Tests

Specimen
(a)

Striking edge 0.25 mm
45 o radius
40 mm
Impact
2 mm

Notch detail (both types)

(b)
Striking edge

Impact
Specimen
10 mm
22 mm

2 mm

Cross section at notch (both types)

Figure 4.35 Specimens and loading configurations for (a) Charpy V-notch, and (b) Izod tests.
(Adapted from [ASTM 97] Std. E23; copyright c ASTM; reprinted with permission.)

In notch-impact tests, the energies obtained depend on the details of the specimen size and
geometry, including the notch-tip radius. The support and loading configuration used are also
important, as are the mass and velocity of the pendulum or weight. Hence, results from one type
of test cannot be directly compared with those from another. In addition, all such details of the test
must be kept constant, as specified in the published standards, such as those of ASTM.

4.8.2 Trends in Impact Behavior, and Discussion

Polymers, metals, and other materials with low notch-impact energy are generally prone to brittle
behavior and typically have low ductility and low toughness in a tension test. However, the
correlation with tensile properties is only a general trend, as the results of impact fracture tests
are special due to both the high rate of loading and the presence of a notch.
Many materials exhibit marked changes in impact energy with temperature. For example, for
plain carbon steels of various carbon contents, Charpy energy is plotted versus temperature in