4 Nov 2026
4 min read
1. Identify the Applicable Standard and Specimen Type
There is no single minimum thickness that applies to every Charpy test: the governing standard, material specification, specimen type and acceptance criteria determine the permitted dimensions. Confirm these requirements first, then select the matching Charpy Impact Testing Machine setup and reporting method.
Check the test request for the standard and edition, full-size or sub-size specimen, notch type, test temperature and any acceptance limit. Do not substitute an Izod impact test procedure: the Charpy and Izod test methods use different specimen arrangements and cannot be treated as interchangeable.
2. Check Whether the Material Meets the Minimum Thickness
Compare the available material thickness with the specimen dimensions permitted by the specified standard. If it cannot supply a full-size specimen, use a sub-size specimen only when the standard and test requirement allow it, and report its dimensions clearly.
A thinner specimen may produce results that cannot be compared directly with full-size results. Before machining, confirm whether the contract, product specification or laboratory procedure accepts sub-size testing; do not assume that a reduced specimen is equivalent.
3. Machine the Specimen to the Required Dimensions
Machine the specimen’s length, width and thickness to the dimensions and tolerances specified for its selected size. Measure the finished cross-section and length with suitable calibrated measuring equipment, and record the measurements before testing.
Avoid rounding dimensions to make a specimen appear compliant. Burrs, uneven faces or a wrong cross-section can affect seating and comparison. Keep specimen identification linked to the material batch and orientation, especially when several sizes or conditions are tested.
4. Cut the Notch in the Correct Orientation
Use the notch type and orientation specified by the test method and material requirement. Mark the specimen’s material direction before machining, then check that the notch faces the correct way relative to the supports and striker.
Inspect notch geometry and finish against the required dimensions; a worn or incorrectly set cutter can change the notch root. Do not infer orientation from the fixture alone. Record the direction and notch details so results from the Charpy test can be compared meaningfully.
5. Control Specimen Temperature Before Impact
Condition specimens to the required test temperature and keep handling consistent from conditioning to impact. Record the target temperature, measured temperature and any timing or transfer controls required by the applicable procedure.
Delays or inconsistent transfers can make temperature comparisons unreliable, particularly when specimens are tested at different temperatures. Use the laboratory’s defined conditioning and transfer process rather than assuming room temperature is suitable.
6. Verify the Machine and Align the Specimen
Check the machine’s verification status, supports, striker and setup before testing; then seat the specimen in the required orientation. Confirm that the notch faces the striker as specified and that the specimen rests correctly on both supports.
Misalignment, incorrect support spacing or a damaged striker can undermine comparisons even when specimen dimensions are correct. Follow the machine procedure and applicable standard, and keep verification and setup records with the test data. For equipment information, see Akuracy’s material testing equipment.
7. Record Impact Energy and Specimen Details
Record the absorbed impact energy alongside specimen size, actual thickness, notch orientation, test temperature, material identification and machine details. Compare results only when specimen geometry, temperature and test conditions are sufficiently aligned.
For a Charpy and Izod test comparison, label the method explicitly: values from different test arrangements should not be presented as directly equivalent. Retain individual readings and any required calculations or report output so another reviewer can trace the result to the specimen and setup.
Charpy Test FAQs
Why is the Charpy test required?
A Charpy test measures the energy absorbed when a notched specimen is struck, helping assess impact behaviour under specified test conditions. It is used when a material or product requirement calls for that evidence.
What is the ISO standard for the Charpy impact test on metals?
ISO 148-1 covers the Charpy pendulum impact test method for metallic materials. Check the current edition and the applicable material specification before preparing specimens or reporting results.
What are the typical results of a Charpy impact test for steel?
Results are commonly reported as absorbed impact energy, but there is no single typical value for all steel. Grade, specimen dimensions, notch, temperature and test conditions affect the result.
What is the minimum thickness requirement for a Charpy impact test?
The minimum thickness is the thickness required for the specimen size permitted by the governing standard and test specification. A sub-size specimen is appropriate only when those requirements allow it.
How to calculate Charpy impact test?
Use the machine’s measured absorbed energy and report it as required by the applicable method; if impact strength per area is specified, divide energy by the specified remaining ligament area. Keep units and specimen dimensions with the calculation.
Recommended next steps
To establish the minimum material thickness for your test, take these steps in order:
- Identify the required standard, edition, specimen size and acceptance criteria.
- Measure the available material and compare it with the permitted specimen dimensions.
- Confirm whether the test requirement accepts a sub-size specimen before machining.
- Check notch, temperature, machine verification and alignment requirements against the procedure.
- Record specimen dimensions and test conditions with every impact-energy result.
- Consult a qualified materials-testing professional if the specification does not clearly allow a specimen size or interpretation.