Pendulum impact testers determine the energy required to break a standardized specimen by measuring the height to which the pendulum hammer rises after impacting the test piece
Impact tests are used to measure the behaviour of materials at higher deformation speeds.
Several test methods are currently applied:.
Charpy impact tests (ISO 179-1, ASTM D 6110).
Izod impact tests (ISO 180, ASTM D 256, ASTM D 4508) and unnotched cantilever beam impact (ASTM D 4812).
Tensile-impact tests (ISO 8256 and ASTM D 1822).
Dynstat tests (DIN 53435).
Within the framework of ISO 10350-1 (single point data) Charpy testing according ISO 179-1 is the preferred test method.
The test is typically carried out with unnotched specimen and edgewise impact (method 1eU).
If the specimens do not break, then the test has do be completed with notched specimens even though the results are not comparable.
If there is still no break, then the tensile-impact method is used.
Within ASTM standards, it is current practice to use the Izod test method according to ASTM D 256, always using notched specimens.
A more seldom used variant is the 'Unnotched cantilever beam impact' method as in ASTM D 4812, which is similar to Izod but specifies the use of unnotched specimen.
If only small specimens are available, then the chip-impact test as per ASTM D 4508 applies.
The Charpy method has a larger range of application and is better suited for testing materials exhibiting interlaminar shear fracture or surface effects.
Also, there are some advantages of the Charpy method when testing at low temperatures due to the increased distance from the specimen notch to the supports which avoids problems of fast heat transfer to that critical part of the specimen.
Some German automotive manufacturers use the Dynstat impact test method for testing of small specimen sizes, however, this method is only described in DIN standards.
Classic impact testers work in a range between 10% and 80% of the nominal energy of the pendulum deployed.
According to ISO standards, the pendulum with the highest possible energy is to be used in order to minimise effects due to the deceleration of the pendulum during impact.
This limits the practical range of use of each pendulum size and often leads to frequent changes of pendulums during a test sequence of different materials.
Zwick impact testers types 5102, 5113 and the new HIT series strictly adhere to ISO and ASTM standards.
They are of the robust design necessary for reliable test results.
Instrumented impact testers.
Instrumentation means that the pendulum fin is equipped with a sensor able to register the forces during the moment of impact.
As a result, supplementary information about the tested material becomes available.
Force / deflection diagrams illustrate the brittleness more precisely.
The range of use of each pendulum size is much larger, so fewer pendulum changes are needed to obtain reliable results in a broad range of tests.
