Charpy impact test

The Charpy impact test is a 1905 by Augustin Georges Albert Charpy established method for materials testing, which ( for Metallic Materials ) and DIN EN ISO 179-1 determined according to DIN EN ISO 148-1 relatively quickly ( for plastic) and just toughness properties of materials. The behavior of an elongated cuboid, which is notched on one side ( usually V, rare U- notch) and the tempered state ( cooled or heated ) is investigated at high strain rate ( impact stress ). The test consists in that a pendulum hammer having a particular kinetic energy is incident on the back of the sample and unnotched smashing it. In this case, at the moment of breaking the sample, a part of the kinetic energy of the hammer is absorbed by deformation processes in the sample. The amount of this energy is different depending on the material and temperature. According to the energy that is absorbed during the battering of the sample, the pendulum hammer swings to the other side is less high. Would he follow through without inserting a sample, it would reach nearly the same height as the starting point. Determines thus the impact energy W in joules, for a given material at a given temperature.

W: Impact energy in Joules m: mass of the pendulum hammer in kg g: acceleration due to gravity ( Earth: 9,81 m / s ² ): Height of fall - rise height of the pendulum hammer ( See sketch of the Charpy impact test )

The deformation capacity of a material can be different under different stress conditions. Therefore, the knowledge of the deformation behavior of the material is an important criterion for material evaluation and selection of materials. In many cases, it has been shown that especially bcc materials that meet at the usual strength test in the ( static ) tensile test requirements, can fail by brittle fracture in practice, for example, under multiaxial stress and lower temperatures. Prior knowledge of the possible strong temperature dependence of the resistance vessels are repeated ( such as the Liberty Freighter ) at low temperature on a calm sea brittle broken apart.

Toughness and brittleness are therefore properties that depend not only on the material but also by the stress conditions such as stress state, strain rate and temperature (see transition temperature). Because of the occurrence of multi-axis and / or sudden stress in technical practice, it is necessary, in addition to elongation and reduction of area, which are determined in the tensile test to investigate the material behavior under Sprödbruchbedingungen.

The determined in Charpy impact test impact energy W goes as well as the deformation parameters A ( elongation at break) and Z ( reduction of area ) from the tensile test are not directly in the strength calculation. Therefore, with the help of these variables only a qualitative statement or a classification with respect to the energy absorption capacity of the material possible.

Measurement methods

Basically, two types of processes are distinguished:

• Tests in which the specimen is supported on two sides and the impact pendulum at the center of the impactor strikes at the level of the notch.
• Tests in which the specimen is vertically incident on the pendulum and the free end of the specimen above the groove.

In the first group the tests according to Charpy and impact tests with hole and double V - groove according to DIN 53 753 fall The second group comprises the tests according to ISO 180 and the IZOD test according to DIN 51 230 Dynstat As for the latter only very small samples ( 10 x 15 mm) are needed, it is particularly suited for component tests, where parts are tested, from which larger samples for other tests can not be removed.