Charpy Impact Resistance of Notched Plastic Specimens: ASTM D6110 & ISO 179

What Is Charpy Impact Testing of Plastics?

The Charpy impact test measures the energy absorbed by a notched plastic specimen when struck by a swinging pendulum hammer. It is one of the primary methods for evaluating the impact toughness of plastics — their ability to absorb energy and resist fracture under sudden, high-rate loading conditions. The notch in the specimen acts as a stress concentrator that ensures fracture initiates at a defined location, making results reproducible and comparable.

Charpy impact testing of plastics is governed by ISO 179 (the primary international standard) and ASTM D6110. It is widely used in the polymer, automotive, electronics, and industrial equipment industries for material selection, quality control, and product development.

Why Notched Impact Testing Is Important for Plastics

The presence of a notch fundamentally changes the fracture behaviour of plastics. A notch increases the local stress concentration, shifts the stress state toward plane strain (triaxial tension), and promotes brittle fracture even in materials that are ductile under unnotched loading. Notched Charpy impact testing, therefore, characterises the material’s worst-case impact behaviour in the presence of stress concentrators such as sharp corners, weld lines, gate marks, or design features in moulded plastic parts.

Materials that absorb high energy in notched impact testing are more damage-tolerant in service when sharp features or impact damage initiate local cracks.

Charpy vs. Izod Impact Testing

Both Charpy and Izod tests use a pendulum to strike a notched specimen, but they differ in specimen mounting and loading geometry:

• Charpy: Specimen is supported at both ends as a horizontal beam; the pendulum strikes the midpoint on the face opposite the notch. Governed by ISO 179 and ASTM D6110.
• Izod: Specimen is clamped vertically as a cantilever; the pendulum strikes the notched face above the clamp. Governed by ISO 180 and ASTM D256.

Both methods provide impact energy data, but are not directly interchangeable due to different loading configurations.

Notch Types and Their Effect on Results

ISO 179 defines three notch types for Charpy impact testing of plastics:

• Type A notch: 45° V-notch, 0.25 mm root radius — the most severe notch, producing the lowest impact energy values and differentiating between brittle materials
• Type B notch: 45° V-notch, 1.0 mm root radius — less severe than Type A
• Notched vs. unnotched: Unnotched Charpy (ISO 179-1/1eU) is used for comparison, as some plastics do not fracture in notched testing

Test Procedure

Specimens (typically 80 mm × 10 mm × 4 mm) are notched by milling or moulding, conditioned at standard temperature and humidity, and placed horizontally across the Charpy anvils. The pendulum is released from a defined height and strikes the specimen. The energy absorbed — measured by the residual swing height of the pendulum — is divided by the cross-sectional area at the notch to calculate notched impact strength in kJ/m².

Factors Affecting Charpy Impact Results in Plastics

Testing temperature profoundly affects results — many plastics undergo a ductile-to-brittle transition as temperature decreases, with notched Charpy impact energy dropping sharply below the transition temperature. Molecular weight, crystallinity, rubber toughening content, fibre reinforcement, and weld lines all significantly influence measured impact energy.

Industrial Applications

In the automotive industry, instrument panel substrates, bumper fascias, and interior trim components are impact-tested at −30°C to validate cold-weather performance. In the electronics industry, ABS and PC/ABS enclosures are impact-qualified to ensure they survive handling and drop events. In materials development, Charpy testing at multiple temperatures generates impact transition curves used to define safe operating temperature ranges.

Conclusion

Charpy impact testing of plastics is a critical method for evaluating how materials behave under sudden, high-speed loading conditions, especially in the presence of stress concentrators. Measuring the energy absorbed during fracture, it provides valuable insight into impact toughness and brittle failure resistance. This makes it an essential tool for material selection, product design, and quality control in applications where impact performance and durability are critical.

Why Choose Infinita Lab for Charpy Impact Testing of Plastics?

Infinita Lab provides Charpy impact testing per ISO 179 and ASTM D6110 at ambient and elevated/reduced temperatures through our nationwide accredited laboratory network. Our polymer testing specialists ensure correct notching geometry, conditioning, and pendulum energy selection.

Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.

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