What Is Charpy?
The Charpy impact test is a dynamic test in which the energy absorbed while a V- or U-notched specimen is fractured by a pendulum hammer is measured. It shows the material's toughness under sudden loading and its brittle-to-ductile transition behaviour.
Purpose of Charpy
The purpose is to numerically determine the material's resistance to impact loads and to assess the risk of brittle fracture, particularly at low temperatures.
Which Products Is Charpy Applied To?
- Structural steels
- Welded joints and the heat-affected zone
- Pressure-vessel materials
- Pipeline steels
- Castings and forgings
In Which Sectors Is Charpy Used?
Standards Related to Charpy
- ISO 148-1
- ASTM E23
- EN 10045
Charpy Conditions
- Specimen cross-section
- 10 mm × 10 mm (standard); a correction is applied for sub-size specimens
- Notch type
- V-notch (2 mm depth, 45°) or U-notch
- Test temperature
- Room temperature or a low temperature per the specification (e.g. −20 °C, −40 °C)
- Support span
- 40 mm
Equipment for Charpy
- Pendulum impact test machine (Charpy)
- Notch-broaching machine
- Low-temperature bath
- Temperature measurement system
Sample Requirements for Charpy
- Standard specimen 10 × 10 × 55 mm
- Generally three specimens per set
- Notch orientation and location are determined according to the specification
- For weld specimens the notch location (weld metal, HAZ) must be additionally specified
Duration of Charpy
The test itself takes a few minutes per specimen. If low temperature is required, conditioning time is added; the typical total for a set is half a working day.
Charpy Procedure
- 1Specimens are prepared to the size and notch defined in the standard.
- 2If required, specimens are conditioned at the test temperature.
- 3The specimen is placed on the supports so that the notch is on the face opposite the hammer's impact.
- 4The pendulum is released and the absorbed energy is read.
- 5The fracture surface is examined; the ductile/brittle ratio and lateral expansion are recorded.
Charpy Acceptance Criteria
The acceptance criterion is given in the material or product standard; it is generally defined as a minimum average energy at a specified temperature, with a lower limit for a single specimen.
Evaluation of Results
The set average and the individual values are evaluated together. The appearance of the fracture surface and the lateral expansion give additional information about the brittle-to-ductile transition.
Charpy Report
- Applied standard and revision
- Specimen size, notch type and location
- Test temperature
- Absorbed energy for each specimen and the set average
- Fracture-surface assessment
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Pressure vessel and structural steel product standards
- Welding-procedure-qualification requirements
Mekanik Testler — What Does This Testing Field Cover?
The section below describes the field that the Charpy test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Mechanical testing measures how a material or a part behaves under force. The family ranges from static loading (tension, compression, bending) to time-dependent behaviour (fatigue, creep), and from hardness and wear to fracture toughness.
What these tests have in common is that the result is reported as a MATERIAL PROPERTY. Yield strength or hardness is not a conformity decision; it is numerical data against which the design and the product standard will compare. Mechanical test reports are therefore usually an input to an engineering decision rather than to a product approval — material selection, safety factor, life prediction.
The distinction between static and dynamic behaviour is the key to understanding the field. A part may appear entirely unstressed under a static load yet break under repeated loading; fatigue fracture occurs at stresses well below the yield strength and gives no warning. For rotating, vibrating or cyclically loaded parts, a tensile test alone is therefore not sufficient evidence.
Test conditions determine the result, and this is critical for the readability of the report: specimen geometry, loading rate, temperature, conditioning and the gripping arrangement. The same material gives different values under different conditions. In plastics the rate effect is very pronounced, in metals the temperature effect; in composites the specimen orientation changes the result entirely.
Hardness is the most misused measurement in the field. Because it is fast, close to non-destructive and inexpensive, it is often used in place of strength. Conversion tables from hardness to strength exist, but they are APPROXIMATE and depend on the material group; using them as the sole evidence in material acceptance is wrong.
The fracture mechanics side requires a specific competence. Fracture toughness and fatigue crack growth rate measurements make it possible to calculate how long a cracked structure will last; they are the basis of damage-tolerant design in fields such as pressure equipment, aircraft structures and pipelines.
Method groups in this field
Static tests
Tension, compression, bending, shear and torsion. Yield and tensile strength, elongation and modulus of elasticity are obtained.
Impact tests
Charpy and Izod notch impact; the brittle-to-ductile transition behaviour of the material is determined as a function of temperature.
Hardness
Brinell, Vickers, Rockwell, Shore and micro hardness. Valuable for surface treatment depth and local differences in strength.
Fatigue
Force- and strain-controlled axial fatigue, fatigue in bending; S-N curves and the endurance limit.
Creep and stress relaxation
Behaviour under long-term load at high temperature; decisive for boiler, turbine and pressure equipment materials.
Fracture mechanics
Plane-strain fracture toughness, the J integral, CTOD and fatigue crack growth rate.
Wear and friction
Taber and rotating drum abrasion, coefficient of friction measurements.
Commonly confused in this field
- Calculating strength from hardness is approximate; it cannot be used as the sole evidence in material acceptance.
- Adequate static strength does not demonstrate fatigue strength; a cyclically loaded part requires a separate test.
- If test rate and temperature are not reported, the result cannot be compared — especially for polymers and composites.
- A test specimen and the actual part may not give the same value; moulding orientation, weld lines and differences in surface treatment all have an effect.
- A strength value given for a composite without stating the specimen orientation is meaningless.
- ASTM and ISO counterparts measure the same quantity but use different specimen geometries; the results are not treated as directly equivalent.
Which decisions these results support
- Design verification and material selection
- Incoming material control and supplier approval
- Meeting the mechanical requirements of the product standard
- Failure analysis, life prediction and damage tolerance calculation
- Verifying heat treatment and surface treatment processes
Related Tests
Frequently Asked Questions About Charpy
What is the difference between Charpy and Izod?
Both are pendulum impact tests. In Charpy the specimen is horizontal and supported at two points, with the impact striking opposite the notch; in Izod the specimen is clamped vertically as a cantilever and the impact is applied on the notch side. Results cannot be converted between the two.
How many specimens are required?
A set of three specimens per temperature is generally required. If a transition-temperature curve is to be produced, sets at several temperatures are required.