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Izod Impact Strength - ASTM D256 Plastic Test Standard

Izod Impact Strength - ASTM D256

Energy per unit thickness required to break a test specimen under flexural impact. Test specimen is held as a vertical cantilevered beam and is impacted by a swinging pendulum. The energy lost by the pendulum is equated with the energy absorbed by the test specimen.

Notes:

  • Charpy Impact Strength is no longer covered under this test method, but is included because Charpy values are still reported under this method.
  • Unnotched Izod Impact Strength, covered by ASTM D4812, is included here because it is often cited as being tested by ASTM D256.
  • Optional units of energy per unit area are supported by the standard. These are the ISO style units.

Notched Izod Specimen

Method Name Test Description Diagram
A Notched Izod Impact Strength Specimen is held as a vertical cantilevered beam and is broken by a pendulum. Impact occurs on the notched side of the specimen.
B Charpy Impact Strength Specimen is held as a simply supported beam and is impacted on the side opposite the notch. This method is no longer covered under ASTM D256 but is still reported as such.
C Estimated Net Izod Impact Strength This method is the same as Method A except that the energy required to toss the broken portion of the specimen is included in the energy calculation. Preferred over Method A for materials with impact strength below 27 J/m (0.5 ft-lb/in)
D Notch Radius Sensitivity Test Provides an indication of notch sensitivity. Notch sensitivity is calculated using:
b = (E2 - E1) / (R2 - R1)
where b is the notch sensitivity, E1 and E2 are the energy required to break a small and large radius notched specimen, and R1 and R2 are the radii of the small and large radius notches. Units are J/m/mm of notch radius.
E Reversed Notched Izod Impact Strength Same test as Method A except the specimen is impacted on the side opposite the notch.
  Unnotched Izod Impact Strength Unnotched specimen is held as a vertical cantilevered beam and is broken by a pendulum. This method is covered under ASTM D4812 but is commonly reported under ASTM D256.

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