Charpy vs Izod Impact Test: Key Differences for Rigid Plastic Testing

October 22, 2026

When evaluating the impact toughness of rigid plastics, two common pendulum impact tests are widely adopted: Charpy test and Izod test. Many buyers confuse these two methods, as both use a pendulum hammer to strike notched samples and calculate energy absorbed during fracture. However, their specimen setup, test principles and applicable scenarios are totally different, and test values cannot be compared directly.

Charpy Impact Test (ISO 179 / ASTM D6110)

The Charpy impact test is a simply supported beam test. The specimen is placed horizontally on two supports without clamping. The pendulum hits the middle of the sample, on the opposite side of the notch.

This standard is more commonly used in Europe for rigid plastics, fiber-reinforced composites and plastic sheets. Without clamping, sample loading is faster, which improves lab testing efficiency. The result unit is kJ/m².

It simulates impact loads on beam-type parts supported at both ends.

Izod Impact Test (ISO 180 / ASTM D256)

The Izod test is a cantilever beam impact test. The plastic specimen is clamped vertically at its lower end, while the upper end remains free. The pendulum strikes the free end of the sample. The notch faces the pendulum, and tensile stress occurs on the notched surface when hit.

This method is popular among North American manufacturers. It simulates real-world conditions where a component is fixed at one end and suffers sudden impact. Typical samples include plastic injection molded parts, modified plastic pellets and small structural components. Test results are usually expressed in J/m.

The main drawback: each specimen needs tight clamping. Improper clamping force will affect the final test data.

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