ISO 180 Izod impact strength and Izod notched impact strength on plastics

The basic features of the method for measuring Izod impact strength to ISO 180 are based on ASTM D256, however, it uses different specimen dimensions and provides a normative framework for both the measurement of impact strength on unnotched specimens, and notched impact strength and notch sensitivity on notched specimens.

The ISO 180 standard supports the commonly used edgewise impact, as well as the less common flat-sided impact. When testing long-fiber-reinforced composites, an additional distinction is made between an impact perpendicular to the fiber direction and an impact parallel to the fiber direction, depending on the fiber orientation.

Pendulum impact testers, which are specified in detail in the ISO 13802 standard, are used for conventional Izod impact tests. 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 for the Charpy method, 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.

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. 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.