Izod Impact Strength - ASTM D256
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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. |
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| 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. |
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| 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) |
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| 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. |
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| E |
Reversed Notched Izod Impact Strength |
Same test as Method A except the specimen is impacted on the side opposite the notch. |
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| |
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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