Izod (Impact)

What is an Izod pendulum impact test?

A test for determining toughness, or the tendency of a material to resist breaking on being subjected to sudden shock. It involves notching a bar on the test specimen, clamping one end (in a cantilever beam configuration) and striking the other end so it breaks off.

How is an Izod pendulum impact test performed?

Typically executed on a pendulum testing machine, Izod impact test can be performed on both notched or unnotched specimens by the support. It is standardized in the ISO 180 and ASTM D256. The test specimen is clamped into the specimen support in a position so that the notched end of the specimen is facing the striking edge of the pendulum. A properly positioned test specimen is showed in the following figure.
Once the pendulum is released, it strikes the specimen and swing through. If the specimen does not break, a higher energy hammer has to be used and the test should be repeated until failure is observed. For the Izod test, pendulum hammers according to standard ISO 13802 are used with a nominal impact energy range from 0.5J to 50J and impact velocities of 3.5 m/s. The impact strength (resilience) is calculated directly by dividing the impact value obtained from the measure by the thickness of the specimen (dimension J/m) or by the residual area under the notch (dimension kJ/m2).

This test method gives a higher stress than a Charpy test and may require a controlled clamping force for good repeatability. The manual specimen support can be tightened using a torque wrench while the clamping force can be adjusted using the lever or pneumatically-operated specimen supports.