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Who searches this and what they need: lab staff, materials students and buyers of test services who need to know what a Charpy test measures, what the machine and specimen look like, how the result is read, and how the machine is kept in verification.
The Charpy impact test is a high strain-rate test in which a controlled pendulum strikes a notched specimen and the energy absorbed in breaking it is recorded in joules. It is mainly used to classify metals, especially ferritic steels, as brittle or ductile. The method is standardised as ASTM E23 and ISO 148 (TWI, read 2026-11-07).
What the Charpy impact test is
ASTM E23 covers notched-bar impact testing of metallic materials by the Charpy (simple-beam) and Izod (cantilever-beam) methods, including specimens, procedures, reports, test machines and machine verification (ASTM E23 abstract, read 2026-11-07). The notched specimen is struck by a single blow, which produces a multiaxial stress state at the notch, usually at a high loading rate. ASTM states that, when correlated with service experience for some materials and temperatures, the results have been found to predict the likelihood of brittle fracture accurately. The standard does not address testing below -196 C (77 K).
Who invented the Charpy test?
The test is named for the French engineer Georges Charpy, who is credited with redesigning the pendulum machine and introducing a notched sample with precise specifications around 1901. Earlier pendulum work by S. B. Russell in 1896 to 1898 used unnotched specimens. The notch is credited with improving accuracy and reproducibility. Charpy’s own tests were run at room temperature or above; the ductile-to-brittle transition concept came later (history summarised by ZwickRoell and a fastener-industry history article, read 2026-11-07).
How the machine and specimen work
A pendulum with a striker is released from a fixed height and swings through the specimen, which is supported at both ends (a simple beam) with the notch on the face opposite the strike. The machine reports the energy absorbed in fracture. For Charpy V-notch (CVN) testing, TWI describes the standard specimen as 55 mm long and 10 mm square, with a notch 2 mm deep and a 0.25 mm tip radius cut in one face. Sub-size specimens thinner than 10 mm are possible (TWI, read 2026-11-07).
Three specimens at a single temperature are normally tested and averaged, or a range of temperatures is tested to build a ductile-to-brittle transition curve (TWI).
What is CVN testing?
CVN stands for Charpy V-notch: a Charpy test on a specimen with a V-shaped notch. The result is the absorbed energy in joules, often quoted as the “CVN value” at a stated test temperature (TWI).
Types and variants
| Variant | What differs | Source |
|---|---|---|
| Charpy | Simple-beam: specimen supported at both ends, struck opposite the notch | ASTM E23 abstract |
| Izod | Cantilever-beam: specimen held at one end | ASTM E23 abstract |
| 8-mm striker | Standard striker; NIST reference specimens come in low (14-20 J), high (88-136 J) and super-high (176-244 J) energy levels | NIST Charpy Verification Program |
| 2-mm striker | Covered by ASTM E23 since 2016; NIST SRMs 2197, 2198 and 2199 serve this striker | NIST Charpy Verification Program |
| Miniature specimens | NIST offers KLST SRMs (2216, 2218, 2219) and RHS SRMs (2237, 2238, 2239) | NIST Charpy Verification Program |
Machine verification and calibration
For lab staff, the machine is as important as the specimen. ASTM E23 includes machine verification (Annex A2). The NIST Charpy Verification Program certifies reference specimens and verifies Charpy machines: a laboratory tests the NIST reference specimens on its machine, returns the results, and NIST issues a Verification Letter or suggestions for correction. Three NIST reference machines set the certified value of each lot, and machines certified under ASTM E23 through NIST agree within the greater of 5 % or 1.4 J of one another. ISO 148-2 verification letters are available on request (NIST, read 2026-11-07).
Super-high-energy specimens often do not fully fracture, and anvils should be cleaned after each test because debris inflates the measured energy (NIST). For the wider context of calibration and accreditation, see what calibration is, ISO/IEC 17025 and how to read a calibration certificate.
How to interpret Charpy impact test results
Absorbed energy in joules is always reported; lateral expansion and the percentage of shear (fibrous) versus crystalline fracture are optional additions (TWI). Read the numbers alongside the fracture surface: a bright, crystalline surface indicates brittle fracture and a dull, fibrous surface indicates ductile fracture. Plotting absorbed energy against test temperature gives the transition curve, which shows where a ferritic steel shifts from ductile to brittle behaviour.
The result is qualitative. It ranks and screens materials, but it cannot be used to calculate fracture toughness (TWI). Instrumented Charpy analysis follows ASTM E2298 and ISO 14556 (NIST).
Uses of the Charpy impact test
- Classifying metals, particularly ferritic steels, as brittle or ductile at a given temperature (TWI).
- Finding the ductile-to-brittle transition temperature range by testing across temperatures (TWI).
- Screening materials against service experience where a correlation to brittle-fracture risk is known (ASTM E23).
Common mistakes
- Treating the joule value as fracture toughness: the test is qualitative (TWI).
- Reporting a single specimen instead of the average of three at one temperature (TWI).
- Not cleaning the anvils between tests, which inflates the energy reading (NIST).
- Applying the method below -196 C (77 K), which ASTM E23 does not address.
FAQ
Who invented the Charpy test?
Georges Charpy, credited with the notched-specimen pendulum design around 1901, building on earlier unnotched pendulum tests by S. B. Russell.
What is CVN testing?
Charpy V-notch testing: a Charpy impact test on a V-notched specimen, reporting absorbed energy in joules.
What are the uses of the Charpy impact test?
Classifying metals as brittle or ductile, mapping the ductile-to-brittle transition, and screening materials for brittle-fracture risk.
How do you interpret Charpy impact test results?
Compare absorbed energy at each temperature, check the fracture surface (crystalline is brittle, fibrous is ductile), and remember the result cannot give fracture toughness.
Sources
- ASTM E23, Standard Test Methods for Notched Bar Impact Testing of Metallic Materials: store.astm.org/e0023-23.html (abstract read 2026-11-07).
- NIST Charpy Verification Program: nist.gov/mml/acmd/structural_materials/charpy-verification-program.cfm (read 2026-11-07).
- TWI, What is Charpy testing: twi-global.com/technical-knowledge/faqs/faq-what-is-charpy-testing (read 2026-11-07).
- ISO 148-1 and ISO 148-2 are the corresponding international standards, cited by TWI and NIST.
