The Izod and Charpy tests both measure a material’s impact toughness — the energy it absorbs when fractured by a sudden blow — but they differ in how the specimen is held and struck. Choosing the right one matters in materials testing for everything from steel certification to plastics quality control. This guide explains both methods and when to use each.
What is an impact test?
An impact test measures the energy absorbed by a notched specimen when broken by a single swinging-pendulum blow. The energy absorbed (in joules) indicates toughness: a tough, ductile material absorbs a lot of energy, while a brittle material breaks with little. The absorbed energy is found from the difference in pendulum height before and after impact:
Energy absorbed = mg(h₁ − h₂)
where m is the pendulum mass, g is 9.81 m/s², h₁ is the initial height and h₂ the height the pendulum swings to after breaking the specimen.
The Izod test
In the Izod test the specimen is clamped vertically as a cantilever, with the V-notch facing the striking pendulum. The pendulum hits the specimen above the notch. It is widely used for plastics (ASTM D256) and some metals.
The Charpy test
In the Charpy test the specimen is placed horizontally as a simply supported beam, with the notch on the face away from the pendulum. The pendulum strikes the middle of the specimen directly behind the notch. It is the global standard for metals (ASTM E23, ISO 148) and is preferred for low-temperature toughness testing.
Izod vs Charpy: key differences
| Feature | Izod | Charpy |
|---|---|---|
| Specimen orientation | Vertical (cantilever) | Horizontal (simply supported beam) |
| Notch faces | Towards the striker | Away from the striker |
| Point of impact | Above the notch (free end) | Behind the notch (mid-span) |
| Typical specimen | 75 mm long, notch at 28 mm | 55 mm long, notch at centre |
| Main standards | ASTM D256 (plastics), BS | ASTM E23, ISO 148 (metals) |
| Low-temperature testing | Less convenient | Preferred (specimen cooled, quickly placed) |
Which test should you use?
Use the Charpy test for metals, welds, and any application needing low-temperature or ductile-to-brittle transition data — its horizontal mounting makes cooled specimens fast to load. Use the Izod test for plastics and for quick cantilever-style metal checks. Both are run on the same pendulum impact testing machine, often with interchangeable supports.
Applications
Impact toughness data is essential for pressure vessels, pipelines, bridges, and automotive components that must resist sudden shock without brittle fracture. The test complements hardness testing and fatigue testing in a full mechanical-properties workup, and is often run alongside the combined impact and torsion test. See the toughness terms in our engineering lab glossary.
Frequently asked questions
What is the main difference between Izod and Charpy tests?
In the Izod test the specimen is vertical with the notch facing the pendulum; in the Charpy test it is horizontal with the notch facing away from the pendulum.
Why is Charpy preferred for low-temperature testing?
The Charpy specimen sits horizontally on simple supports, so a chilled specimen can be placed and struck within seconds before it warms up, giving accurate ductile-to-brittle transition data.
What does the impact test measure?
It measures impact toughness — the energy in joules a notched specimen absorbs before fracturing under a sudden pendulum blow.
Need an Izod/Charpy impact testing machine for your lab? Request a quote from Scientico India — ISO 9001:2015 certified, CE marked, exporting to 60+ countries, reply within 24 hours.
Lab Equipment Featured in This Guide
Manufactured in-house by Scientico India — ISO 9001:2015 & CE certified, exported to 60+ countries. Request a CIF quote within 24 hours.
Suspension Bridge Apparatus | FortiTestX – 25View details & get quote →
Fatigue Testing Machine | FortiTestX – 22View details & get quote →
Torsion Testing Machine 300Nm (Manual) | FortiTestX – 10AView details & get quote →
Deflection of Beam Apparatus | FortiTestX 06View details & get quote →
Parabolic Arch Apparatus | FortiTestX-27View details & get quote →
Torsion of Bar | FortiTestX – 21View details & get quote →