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
Plastics Testing — 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.
Plastics testing determines the mechanical, thermal and burning behaviour of a polymer material. Unlike metals, plastics are VISCOELASTIC: their behaviour depends on loading rate, temperature and moisture. The same material therefore gives different results under different conditions, and the test conditions are an inseparable part of the result.
The practical consequence of viscoelasticity is this: a plastic part continues to deform over time under a constant load (creep) and the stress it carries at constant deformation falls over time (stress relaxation). A screwed joint loosens, a clamp loses its clamping force, a shelf sags over time. A short-term tensile test does not show this behaviour; a long-term test or an accelerated model is needed.
Thermal behaviour is the second main axis. Melt flow rate indicates the processability of the material and lot-to-lot consistency; heat deflection temperature and the Vicat softening point give a rough limit for service temperature. Thermal analysis (DSC, TGA, DMA) reveals the identity of the material: glass transition temperature, melting behaviour, crystallinity, filler content and decomposition temperature.
Burning behaviour is the third axis and ties directly into product standards. The UL 94 class and the limiting oxygen index are written into the material data sheet; a particular class is required for the housing of an electrical appliance, while a different classification system applies to a construction product.
Ageing is the most frequently skipped part of the field. Plastics degrade under UV, heat, moisture and oxygen: colour changes, the surface cracks, impact strength falls. For a part intended for outdoor use, what matters is not its values on day one but its values after ageing. Xenon arc and fluorescent UV equipment accelerate this degradation and allow comparison.
The output of this family is usually written into the material data sheet, and product standards refer to that sheet. But there can be a difference between the data sheet value and the behaviour of the actual part: orientation formed during moulding, weld lines and internal stresses make the part behave differently from the specimen.
The use of recycled content has added a new question to the field. Recycled resin varies from lot to lot; mechanical properties, colour and burning behaviour can shift between batches. For a manufacturer using recycled material, incoming material control is therefore not a choice but a necessity.
Method groups in this field
Mechanical
Tension, compression, bending, Charpy and Izod impact, hardness (Shore), creep and environmental stress cracking.
Thermal
Melt flow index (MFI), heat deflection temperature (HDT), Vicat softening temperature, linear thermal expansion.
Thermal analysis
Transition temperatures and crystallinity by DSC, composition and decomposition by TGA, dynamic mechanical behaviour by DMA.
Burning
UL 94 classification, limiting oxygen index (LOI), glow wire and needle flame tests.
Ageing
Accelerated ageing by xenon arc and fluorescent UV, hot air ageing, humidity and condensation.
Physical
Density, water absorption, ash content, gas and water vapour permeability of films and sheets.
Commonly confused in this field
- A plastics result without a stated test rate and temperature cannot be interpreted; viscoelastic behaviour depends on these parameters.
- A specimen result does not transfer directly to the actual part; moulding orientation and weld lines are decisive.
- HDT and Vicat values are NOT service temperatures; they are a rough indication of an upper limit and do not apply under load.
- The UL 94 class depends on thickness; a different wall thickness requires re-verification.
- For moisture-absorbing polymers (such as polyamide), results are misleading unless conditioning is carried out.
- ASTM D638 and ISO 527 results are not directly equivalent; the specimen geometries and rate definitions differ.
Which decisions these results support
- Material selection and supplier approval
- Meeting the flammability and thermal requirements of the product standard
- Verifying the use of recycled content and lot control
- Moulding process control and lot consistency
- Demonstrating ageing resistance for outdoor use
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.