1. What Notched Impact Testing Measures
1 Short answer: Run ASTM D256 if your spec sheet, customer or procurement document asks for Izod values. Run ASTM D6110 if the part ships internationally and the data has to line up with ISO 179 (Charpy). The two results are not interchangeable.
The difference in one line: D256 clamps the specimen at one end and hits the free end. D6110 rests the specimen on two supports and hits the middle.
2. Full Comparison
Values shown are the standard configurations. Specimen geometry may vary with material thickness and the version of the standard named in your contract.
| Parameter | ASTM D256 — Izod | ASTM D6110 — Charpy |
|---|---|---|
| Full Title | Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics | Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics |
| Specimen Mounting | Cantilevered — clamped vertically at one end | Simply Supported — resting horizontally at both ends |
| Strike Location | Free end, above the notch | Centre of the span, opposite the notch |
| Notch Orientation | Facing the pendulum (tension side) | Facing away from the pendulum (tension side) |
3. What Notched Impact Testing Measures
What Notched Impact Testing Measures
ASTM D256 — Izod
- Engineering thermoplastics: nylon, ABS, polycarbonate, PVC
- Injection-moulded parts and consumer product housings
- Glass-filled compounds and structural blends
ASTM D6110 — Charpy
- The same general material families as D256
- The go-to method when results are cross-referenced against ISO 179 Charpy data
- Used where international suppliers or customers set the reporting format
4. How Each Test Is Run
Energy absorbed is calculated the same way in both methods — from the reduction in the pendulum's swing height. Everything before that moment is different.
ASTM D256 — Izod
- The specimen is clamped vertically in a vise, notch facing the pendulum, free end upward.
- A calibrated pendulum swings and strikes the free end above the notch.
- Energy absorbed in breaking the specimen is read from the pendulum's residual swing.
ASTM D6110 — Charpy
- The specimen is laid horizontally across two supports, notch facing away from the pendulum.
- The pendulum strikes the centre of the specimen, directly opposite the notch.
- Energy absorbed is calculated from the reduction in pendulum swing height.
5. Testing Equipment
| Equipment | ASTM D256 | ASTM D6110 |
|---|---|---|
| Pendulum Impact Tester | Izod-configured, vertical vise fixture | Charpy-configured, horizontal anvil supports |
| Fixture | Cantilever vise clamp | Two-point simple-support anvil |
| Notching Tool | Single-tooth or milling cutter, standard notch cutter | Same class of notch cutter, Charpy geometry |
| Energy Capacity | Multiple pendulum weights, 0.5–22 J typical | Multiple pendulum weights, 0.5–25 J typical |
6. Applications
ASTM D256 — Izod
- Injection-moulded housings and enclosures for electronics and appliances
- Automotive interior and exterior trim components
- Material QC and incoming-inspection benchmarking for North American suppliers
ASTM D6110 — Charpy
- Global supply chains needing direct comparability with ISO 179 Charpy data
- Engineering plastics for export markets across the EU and Asia
- R&D formulation work where international literature is the reference point
7. Strengths and Limitations
| Standard | Strength | Limitation |
|---|---|---|
| ASTM D256 | Long history of reference data; widely specified in North American procurement documents | Cantilever mounting is more sensitive to clamping pressure and operator variation |
| ASTM D6110 | Simply-supported geometry closely mirrors ISO 179, easing international data comparison | Less commonly specified in legacy North American contracts; fewer historical datasets |
8. Which Standard Should You Run?
| If This Describes You | Run This | Why |
|---|---|---|
| Your spec sheet, customer or industry standard calls for Izod values — or you are benchmarking against historical North American data | ASTM D256 | Matching the method your specification names keeps results directly comparable to the numbers already on file |
| Your part will be sold internationally and needs cross-referencing against ISO 179 Charpy results | ASTM D6110 | The simply-supported geometry lines up with ISO 179, so the data holds its meaning across borders |
| You are not sure which your programme needs | ASTM D6110 | The simply-supported geometry lines up with ISO 179, so the data holds its meaning across borders |
Still unsure? Our lab can run both on the same batch of specimens for direct side-by-side data. Talk to our team.
9. Frequently Asked Questions
Is ASTM D256 the same as ASTM D6110?
No. Both measure notched impact resistance, but D256 uses a cantilevered specimen in the Izod configuration while D6110 uses a simply-supported specimen in the Charpy configuration. Results are not directly interchangeable.
Can I convert Izod results to Charpy results?
Not reliably. Because specimen support and strike geometry differ, there is no universal conversion factor between D256 and D6110 values — each material behaves differently under the two configurations. Testing both is the only reliable way to get comparable data.
Which test is more common in the plastics industry?
ASTM D256 (Izod) remains the more commonly specified method in North America. ASTM D6110 (Charpy) is used more often when a part or resin needs to be compared against international ISO 179 data.
10. Related ASTM Testing Services
| Standard / Page | Description |
|---|---|
| ASTM D256: Izod Impact Resistance Testing Services | Izod Pendulum Impact Testing |
| Charpy Impact Testing | Charpy Impact Testing |
| Tensile Properties of Plastics | Tensile Properties of Plastics |
