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The impact test is a method for evaluating the toughness and notch sensitivity of engineering materials. It is usually used to test the toughness of metals, but similar tests are used for polymers, ceramics and composites.

The test specimen is broken by the impact of a heavy pendulum hammer, falling at a pre-determined velocity through a fixed distance. On impact, the specimen deforms elastically until yielding takes place and the specimen fractures.

The test measures the energy used to fracture the specimen, this depends on the size of the test specimen, therefore, a standard specimen size is used to allow comparison between different materials.

The energy absorbed during fracture is indicated by the degree of over-swing of the pendulum, read directly from the machine dial.

Charpy Test

The most commonly conducted tests are bending impact tests, using one of two kinds of notched specimens. The Charpy specimen is supported at both ends by a standard impact-testing machine and struck on the side opposite to that of the notch. The testing machine is constructed with a weighted pendulum, which is lifted to start the test. Upon its release, the pendulum swings past the specimen, and breaks it. As the pendulum swings past, the remaining energy can be measured by the height of the swing and the absorbed energy determined.

Zod Test

The Izod specimen is supported in the testing machine by one end only and is loaded as a cantilever beam with a notch on the side of impact. Energy absorption is measured in the same way as with the Charpy specimen.
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