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Last Updated on March 12, 2023 by Noaman Adenwala
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The Charpy impact test is a high strain-rate test to find the impact toughness of a material. In the Charpy impact test, a standard notched specimen is struck by a controlled weight pendulum swung from a predefined height. The impact test is required to find out the amount of energy a specimen absorbs during fracture. As the notch prepared in the specimen is generally in the shape of the English letter “V”, the process is also popularly known as Charpy V-Notch Test.
Charpy V-notch test is widely used in industry to understand fracture problems of materials. The test is known as the Charpy test as the French Scientist, Georges Augustin Albert Charpy improved the original impact test introduced by the American Scientist, S B Russel.
What is the Charpy Impact Test used for?
The main purpose of the Charpy impact test is to evaluate the resistance of a material against impact or shock leading. This property of the material is known as toughness. The energy absorbed by the material while fracturing gives a measure of the material’s toughness. The Charpy test provides a tool to study ductile-brittle transition. The test output results can decide whether a material can be called a brittle or ductile material.
Charpy Impact Testing Procedure
Charpy impact testing is performed on a pendulum testing machine. In general, 3 specimens are prepared and the test is performed on all three test specimens to get an average output value. In the Charpy impact testing machine the following steps are followed:
- The pendulum of the calibrated Charpy machine is lifted to the starting position.
- The test specimen is now placed correctly on the machine anvil using the centering device.
- Next, the pendulum mass hammer is released which swings down and hit the specimen to break it.
- The energy absorbed (in Joules) is calculated and tabulated.
- Then the test is performed for specimen 2 and specimen 3 respectively and the average value of absorbed energy is calculated.
While a test is executed, the absorbed energy by the material specimen is calculated from the difference between the pendulum mass height over the specimen before and after impact and the mass of the pendulum hammer itself.
Standards for Charpy Impact Testing
There are various standards that provide rules for Charpy impact testing. The widely used standards for Charpy Impact testing are:
- ASTM E23
- ASTM A370
- ASTM E208
- ASTM D6110
- ISO 148
- MPIF Standard 40
- IS 1757
Charpy Impact Test Specimen
Based on ASTM A370/ISO 148, the standard Charpy impact test specimen size is 10 mm × 10 mm × 55 mm. The Charpy impact test is executed on both notched or unnotched specimens. However, the notched specimen is the most widely used Charpy test specimen.
Again, there are two types of notches; V-notch and U-notch.
- V-notch is a V-shaped notch, 2 mm deep, with a 45° angle and 0.25mm radius along the base, and the common for industrial Charpy tests.
- U-notch or keyhole notch is a 5 mm deep notch with a 1 mm radius at the base of the notch.
In some circumstances, sub-size Charpy test specimens can be prepared with thicknesses less than 10mm. Some of the sub-size Charpy test specimen sizes are
- 10 mm × 7.5 mm × 55 mm,
- 10 mm × 6.7 mm × 55 mm,
- 10 mm × 5 mm × 55 mm,
- 10 mm × 3.3 mm × 55 mm,
- 10 mm × 2.5 mm × 55 mm.
Parameters affecting Charpy Impact Energy
Various factors affect the Charpy impact energy of the material. They are as follows:
- Yield strength: With an increase in the yield strength of the material, the impact energy decreases.
- Ductility: With an increase in ductility, the impact energy increases.
- Notches: Proper standardized notch dimensions are important for getting accurate output results.
- Temperature and strain rate: The test is generally performed at 230C (+/-50C). Different temperatures affect the ductility of the material.
- Fracture mechanism
Charpy Impact Testing Machine
The Charpy impact testing equipment is known as a pendulum impact tester. The apparatus consists of a pendulum of known mass and length. Fig. 1 below provides an image of a typical Charpy impact test machine.
Difference between Charpy Test and Izod Test
There are two types of Impact Tests used in industries; the Charpy Test and the Izod Test. While the Charpy test is widely used for metals, the Izod test is more popular for non-metals. The following table lists the major differences between the Izod test and the Charpy test:
|Charpy Impact test||Izod Impact test|
|The specimen notch in the Charpy impact test can be a V-notch or a U-notch.||Izod impact test uses only V-notch on the specimen|
|In the Charpy impact test, the specimen is held horizontally||On the other hand, in the Izod impact test, the specimen is held vertically.|
|The Charpy impact test is used for metallic materials.||Izod impact test can be used for plastics and metals both.|
|The striking point in the case of Charpy impact testing is in the middle of the specimen.||Whereas the striking point in the case of the Izod test is at the upper part of the sample.|
|The specimen size in the case of the Charpy test is 55*10*10 mm||The specimen size in the Izod test is 75*10*10 mm|