In a Charpy impact test, a material specimen is fractured using a Charpy pendulum impact tester. For the test, the specimen is centered in the pendulum impact tester and struck with the pendulum hammer and fractured.
The Charpy impact test is a destructive test method that is used for the characterization of a material at high strain rates. It is performed on plastics as well as metals.
Charpy impact tests provide characteristic values for the impact strength of a material at high strain rates in the form of a surface area related energy value. The tests are normally performed at ambient temperature or a low temperatures.
The Charpy impact test is carried out in a 3-point flexure setup. The Charpy specimen is centered on the supports in the pendulum impact tester and rests against two anvils. In the case of notched specimens, the notch faces away from the pendulum hammer and is placed exactly across from the point at which the hammer strikes the specimen.
The pendulum hammer strikes the specimen with a defined energy and fractures (destroys) it with a single hit. As the specimen is fractured, the pendulum hammer transfers part of its kinetic energy and is therefore unable to return to its original drop height. The measured height difference is the value for the absorbed energy. In instrumented Charpy tests, the impact energy expended is determined by recording a force-time sequence or a force-travel sequence.
The supports provide a horizontal plane in the pendulum impact tester on which the Charpy specimen is placed.
The anvils provide a vertical plane in the pendulum impact tester, against which the Charpy specimen rests during the test.
The striking edge, or striker, is the part of the pendulum hammer that hits the Charpy specimen.
Center of striker
The center of striker is located on the striking edge of the pendulum and strikes the Charpy specimen exactly opposite to the notch or in the center of the specimen (unnotched specimens).
Impact energy is defined as the energy required to fracture the Charpy specimen. The impact energy is determined from the difference of the potential energy of the pendulum hammer and the angle of fall of the pendulum hammer after the specimen is fractured.
The impact strength (also referred to as notched impact strength) is determined through Charpy testing, and provides information on how resistant a material is to an impact load, or how well a material can handle an impact without breaking. Notched impact strength is displayed in J/cm²
Force-travel curve / Force-time curve
Determination of the force-time curve is only possible when using an instrumented Charpy impact test. In an instrumented test, the force is measured during the impact, for which either Piezo load cells or strain gauges are used, depending on the application.
Instrumented Charpy testing can be used to determine parameters in addition to those determined in the non-instrumented test:
- Maximum force
- Deflection at maximum force
- Energy up to maximum force
- Deflection at break
- Energy at break
Since fracture or failure behavior depends on temperature, Charpy impact tests are often performed in the entire operating temperature range. This shows at what temperature and to what extent the material becomes brittle (tough-to-brittle transition).
The example diagram shows that the decrease in strength of mild steel at -40 °C is 25 % in relation to the strength at 0 °C. Plastics display a similar behavior, but generally considerably more pronounced. Impact tests are also frequently carried out on plastics at various temperatures.
In order to determine the process of impact strength in relation to temperature with accuracy, tempered specimens must be struck within 5 seconds of removing them from the temperature conditioned environment.
Charpy impact tests can also be automated. An automated solution provides the benefit of eliminating operator influences such as hand temperature or moisture and off-center or angled specimen insertion, which in turn results in high reproducibility of the test results. Automatic alignment of the specimens with the supports and starting the test via the testing system also ensures reliable and reproducible results.
The robotic testing system roboTest I supports the user in the performance of Charpy impact tests on metals. The system can be used to automatically test up to 450 notched metal specimens in a temperature range of -180 °C to +300 °C. A solid and insulated temperature conditioning unit ensures uniform and accurate specimen temperature.
The robotic testing system roboTest H performs automated Charpy impact tests on plastics. The impact tests are performed at ambient temperature or on cooled specimens.
In a Charpy v-notch test, the specimen is placed horizontally in the pendulum impact tester and struck through the center. In an Izod impact test, the specimen is vertically gripped in the pendulum impact tester and the pendulum hammer breaks off the top part of the specimen.
In contrast to the Izod test, the Charpy impact test has a broader range of applications and is better suited to test materials displaying interlaminar shear fractures or surface effects. In addition, the Charpy method offers advantages when testing at low temperatures. Since the specimen supports are further away from the notch, rapid heat transfer to the critical areas of the specimen is avoided, simplifying the cooling process in an external cooling device and subsequent feeding into the testing instrument.
The Charpy impact test measures the impact energy of materials, which is then used to determine the impact strength.
The Charpy impact test is used for the determination of the notched impact strength, which indicates how resistant a material is to dynamic impact loads.
The Charpy impact test, also referred to as Charpy v-notch test, is a materials testing method used to determine the impact strength of materials using a pendulum impact tester.
The Charpy impact test provides characteristic values for the impact strength at high strain rates in the form of a surface area related value. The test measures the impact energy in relation to the fracture surface in joules.
The impact strength is calculated using the following formula: Notched impact strength = impact energy / (specimen thickness * specimen width)
In a Charpy impact test, a pendulum hammer strikes a material specimen and destroys it. During this process, the specimen absorbs part of the impact energy. This impact energy W determined in the Charpy test is measured in joules.