ISO 8256 | ASTM D1822 Tensile Impact Test

Pendulum impact testers, which are defined in detail in the ISO 13802 standard, are used for conventional tensile impact tests in accordance with ISO 8256 and ASTM D1822. This supports a strong level of reproducibility of tests performed using different types of test equipment and different laboratories, operators and locations.

As is the case with the Charpy impact test ISO 179 ASTM D6110, the measurement principle is based on a pendulum hammer with specified energy capacity and drop height, which releases part of its kinetic energy when it penetrates the specimen. As a result, the pendulum hammer does not return to the original drop height after the impact. The measured height difference between drop height and height of rise therefore becomes a measure of the energy absorbed. By determining the drop height, the impact velocity is also defined so that the tests are performed with reproducible strain rates.

A special feature of the tensile impact test is correction of the centrifugal work absorbed by the yoke. This correction is based on the assumption of an elastic impact. In practice, however, there is an impact that has a plastic component in addition to the elastic component, so this correction remains an approximation. A direct comparison of characteristic values should therefore be carried out on an identical pairing of pendulum hammer and yoke size.

Each pendulum hammer may be used in a range of 10% to 80% of its initial potential energy. If several pendulum hammers meet this condition for testing a material, which is usually the case from the overlapping working ranges of the various pendulum hammers, the pendulum hammer with the greatest initial potential energy is used. This ensures that the reduction in speed during the impact process is minimized.

The type of measurement implies that all energy losses are attributable to the specimen and the yoke. It is therefore important to minimize, correct, or completely eliminate all external sources for error. There are strict specifications in ISO 13802, as well as checks that are part of regular calibrations, regarding friction losses that inevitably occur due to air friction and friction at the bearing points of the pendulum hammer. The correction values are measured and assigned to the respective pendulum hammer. Sufficient mass and a vibration-free installation of the pendulum impact tester on a very stable laboratory table, on a worktop bolted into a solid wall, or a masonry platform are essential for the quality of the measurement. Internal vibrations in the instrument are minimized by design. ZwickRoell uses pendulum hammers with double rods made of unidirectional carbon materials, which are very low in mass and at the same time offer optimum stiffness of the pendulum rods.