The ASTM E23 standard describes Charpy and Izod impact tests on notched bar metal specimens. For the test, a notched metal specimen is broken in half using a pendulum hammer. The ASTM E23 standard describes the requirements for specimens, for the performance of the test, for result reports and for testing machines, i.e., pendulum impact testers at ambient temperature as well as high and low temperature conditions.
A further description of the Charpy pendulum impact test on notched bar metal specimens can be found in the ISO 148-1 standard.
The objective of the notched bar impact test to ASTM E23 is determination of the impact energy and impact strength of a metal. With this test method, you can test whether a metal is tough or brittle. In the notched bar impact test, a one-time force with a large load is applied to the metal specimen, resulting in multiaxial stresses. Tests are performed at high or low temperatures. The objective of the test is to accurately predict the probability of a brittle fracture.
In the Charpy impact test, the metal specimen is centered on the supports in the pendulum impact tester. The notch faces away from the pendulum hammer and is placed exactly across from the point at which the hammer strikes the specimen. This impact test is used to determine the absorbed impact energy.
For the Izod impact test, the metal specimen is gripped vertically in the pendulum impact tester. The notch is placed at the level of the grips, and faces the hammer. The pendulum hammer breaks off the non-gripped end of the specimen. The standard recommends that Izod impact tests should only be carried out at ambient temperature, since the gripping fixture is often part of the pendulum impact tester and cannot be tempered accordingly.
The decision on which method to use (Charpy or Izod) is normally specified by product standards or by the customer.
ASTM E23 indicates that these specimen shapes may not be suitable for cast materials.
For structural materials produced by powder metallurgy, specimens without notches can be used for both the Charpy and Izod methods.
If the production of standard impact test specimens is not possible, smaller ones, referred to as sub-size specimens are treated as standard specimens in the normative annex. These vary in width, bar width at notch, and height, however, in fixed increments. The test report must refer to the dimensions used.
Often, notched bar impact tests are performed at high or low temperatures. These test temperatures are selected to characterize the material behavior in the respective temperature range. A change in material properties with changing temperatures also provides interesting information for materials testers.
If the notched bar impact test is performed at a high or low test temperature, no more than 5 seconds may elapse between removal of the specimen from the tempering medium and the impact of the hammer on the specimen.
In addition, you must ensure that the temperature of the specimen does not significantly change during transport to the pendulum impact tester. The standard recommends the use of temperature-conditioned, self-centering tongs for placement of the specimens. For larger specimen batches, an automated testing system is recommended for temperature-conditioning, transport, placement, and automatic testing of the specimens.