The notch impact test, commonly called the Charpy test, determines a material’s toughness under dynamic loading by measuring the energy a notched specimen absorbs when it is broken by a single blow of a pendulum. The absorbed energy is expressed in joules (J) and depends on specimen size and test temperature. FKT NDT provides Charpy impact testing for parent materials and welded joints.
What Does the Charpy Test Measure?
The main result is the energy absorbed in breaking the specimen (for example KV2 for a V-notch specimen). It indicates how well a material resists brittle fracture under sudden loads and at low temperatures. The fracture surface of the broken specimen also gives information on the fracture type:
- Ductile fracture: fibrous, dull surface, indicating high absorbed energy.
- Brittle fracture: bright, crystalline surface, indicating sudden fracture at low energy.
- Mixed fracture: both features present; the percentage of shear (ductile) fracture can be reported if required.
Testing at a series of temperatures shows the ductile-to-brittle transition behaviour of the material.
Where Is It Used?
- Welding procedure qualification (WPQR): specimens from the weld metal and heat-affected zone verify the toughness of the welding procedure.
- Material acceptance: especially for steel structures, pressure equipment, pipelines and shipbuilding materials operating at low temperature.
- Production control and failure investigation: assessing the effect of heat treatment or production conditions on toughness.
In weld qualification programmes, impact tests normally run alongside tensile tests, bend tests and macro examination.
Standards
Charpy impact testing is commonly applied according to:
- ISO 148-1: Metallic materials – Charpy pendulum impact test – Test method
- ISO 9016: Destructive tests on welds in metallic materials – Impact tests (specimen location, notch orientation and reporting)
- ASTM E23 and ASTM A370: for projects working to American standards
- ISO 15614-1: when impact testing is required in procedure qualification, and its acceptance criteria
How the Test Is Performed
- Specimen preparation: the standard specimen measures 10 × 10 × 55 mm with a V-notch, usually 2 mm deep, at mid-length. Sub-size specimens can be used for thin material. In welds, the notch is placed at the required location: weld metal, fusion line or heat-affected zone.
- Temperature conditioning: specimens are brought to and held at the test temperature given in the specification.
- Impact: the specimen is placed on the supports and broken by a single swing of the pendulum; the absorbed energy is read.
- Evaluation: the average of a set, usually three specimens, and the individual values are compared with the specified minimums.
- Reporting: the report gives specimen dimensions, notch type and location, test temperature, individual and average energy values and, if required, fracture appearance.
FAQ
Why is the Charpy test done at low temperature?
Many steels change from ductile to brittle behaviour as temperature falls. The test is done at the lowest relevant service temperature to confirm the material still has adequate toughness there.
What is the difference between Charpy and Izod?
Both are pendulum impact tests. In Charpy the specimen is supported at both ends and struck behind the notch; in Izod it is clamped at one end. Charpy is the usual method for metals and welds.
Is the Charpy test the same as the nick-break test?
No. The Charpy test measures toughness in joules. The nick-break test breaks a weld open to inspect the fracture surface for internal imperfections and does not measure energy.
How many specimens are tested?
A set of three specimens per location and temperature is typical. The exact number is set by the applicable standard and specification.
To arrange Charpy impact testing, contact us with the material, test temperature and standard, and we will prepare a quotation.