ISO 148-1: Charpy impact test on metals
The notched bend test according to ISO 148 is used to determine the impact energy and the brittle fracture behavior of metallic materials. This method is particularly relevant for applications in which materials must reliably absorb shock and impact loads. It is used in quality assurance, materials development, production control, and accreditation.
In practice, variations often result from inaccurate specimen dimensions, notch quality, temperature fluctuations, or operator influence. ZwickRoell supports you with the right pendulum impact testers, insertion aids, temperature conditioning solutions, the testXpert testing software, and automation options.
The test method is also described and determined in ASTM E23. The ISO standard is identical to the European standard (EN ISO 148-1).
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ISO 148-1 – Key facts at a glance
- ISO 148-1 describes the Charpy impact test on notched metal specimens with a U- or V-notch and is used to determine impact energy and impact toughness.
- The test indicates whether a metal behaves in a ductile or brittle manner; in addition, the ductile-brittle transition can be determined as a function of temperature.
- In practice, the greatest sources of error are related to specimen dimensions, notch depth, notch position, surface quality, incorrect specimen orientation, and insufficiently controlled temperature conditions.
- Temperature-controlled tests are challenging because the specimen must be tested within a few seconds after being removed from the temperature-conditioning environment.
- The correct pendulum size, standard-compliant impact velocity, calibrated anvils, and compensation for friction and air resistance losses are crucial for comparable results.
- ZwickRoell offers pendulum impact testers, Charpy impact fixtures, insertion aids, temperature conditioning solutions, and automationsuitable for testing in accordance with ISO 148.
- The testXpert testing software supports standardized test procedures, reliable parameter configuration, traceable documentation, and the integration of test data into laboratory processes.
ISO 148-1 in practice: Common sources of error and their influence on test results
In practice, the quality of a notched-bar impact test is not determined by the pendulum impact tester alone Variations often arise even before impact, during specimen preparation, temperature conditioning, or manual specimen insertion. It is precisely these steps that determine whether results are comparable, reproducible, and reliable.
Possible sources of error in:
Specimen Preparation & Specimen Quality Insertion & Alignment Temperature Influence Testing System
Specimen preparation and specimen quality
Common sources of error:
- Non-compliant specimen dimensions: Standard Charpy specimens measure 10 × 10 × 55 mm. Deviations alter the fracture behavior and make it difficult to compare the results with reference values.
- Defective or uneven notch: Notch depth and notch radius significantly affect the measured energy. A smaller notch can result in higher impact energies, while a larger notch can result in lower values.
- Off-center notch: In the Charpy test, the notch must be centered so that the pendulum hammer strikes the opposite side with precise accuracy.
- Confusion between V- and U-notches: Due to their different geometries, V-notches and U-notches yield results that cannot be compared.
- Surface defects and scratches: Damage or scratches can affect crack propagation and, in the worst case, can also damage the anvils.
- Material inhomogeneity or incorrect batch:Different material conditions have a direct effect on the absorbed energy and the percentage of brittle fracture.
Temperature control and time window
Temperature-controlled tests in accordance with ISO 148 are particularly critical because the fracture behavior of metallic materials can change significantly with temperature. Many metals become more brittle, especially at low temperatures; therefore, the specimen must actually be at the required test temperature at the moment of impact.
Critical points are:
- Uniform temperature conditioning of the specimen: The specimen must be conditioned to a uniform temperature throughout, not just at the surface.
- Rapid transfer to the test:No more than 5 seconds may elapse from removal from the temperature-conditioning environment, through insertion into the impact fixture, to impact by the pendulum.
- Temperature loss due to handling:Ambient temperature, handling, and non-temperature-conditioned auxiliary equipment can alter the specimen temperature.
- Temperature-conditioned tongs:For low-temperature tests, the gripping tongs should also be temperature-conditioned so that the specimen is not warmed when gripped.
- Reproducible specimen insertion:Under time pressure, there is an increased risk that the specimen will not be inserted exactly in the center or with the correct orientation.
If the specified time window is exceeded, it can no longer be ensured that the test is performed at the defined temperature. This can lead to variations and compromise the comparability of the results.
Pendulum impact tester, pendulum capacity, and impact velocity
The testing system itself must also be suitable for the standard and the test task:
- ISO 148 requires an impact velocity in the range of 5 to 5.5 m/s.
- The release angle and the pendulum hammer affect the impact velocity and, consequently, the comparability of the results.
- Anvils are subject to wear during testing and must be inspected regularly and cleaned, rotated, or replaced as necessary.
Would you like to perform ISO 148 tests more reliably, reproducibly, or efficiently?
We can assist you in selecting the pendulum impact tester, impact fixture, temperature-conditioning solution, software, and level of automation to suit your material, specimen volume, test temperature, and standard requirements.
Performing the notched bar impact test to 148-1 with ZwickRoell
Critical test steps and ZwickRoell testing solutions explained in detail:
Specimen positioning Temperature control Selection of pendulum impact tester Selection of impact fixture Energy losses Automation options
Here’s how the test works:
In the Charpy notched bar impact test according to ISO 148, a notched metal specimen is placed on two supports and fractured by the impact of a pendulum hammer. The notch is positioned in the center, with the impact occurring on the opposite side.
Before the test, the specimen geometry, notch type, notch depth, surface condition, and, if applicable, the test temperature are prepared and checked. For temperature-controlled tests, the specimen must be conditioned to a uniform temperature throughout and must be inserted and tested within 5 seconds after removal from the temperature-conditioning environment.
The absorbed energy in joules is determined from the difference between the pendulum's drop height and its rise height. In addition, the percentage of brittle fracture on the fracture surface can be evaluated, for example, manually or optically. The results are used for material comparison, quality control, and the evaluation of material behavior under impact loading.
Position specimens precisely
Centering the specimen is essential for reproducible results. Even small deviations in position alter the point of impact of the pendulum hammer and, consequently, the local stress. Tongs, stops, or centering aids make it easier to insert the specimen quickly and reproducibly and reduce deviations during manual positioning.
In automated impact tests, the testing system handles the positioning of the specimen. This ensures that the specimen is in the same position for every test. As a result, test conditions remain consistent, providing the basis for comparable and reproducible results.
Maintain reliable temperature control
For temperature-conditioned specimens, no more than 5 seconds may elapse between removal of the specimen and impact by the pendulum hammer. Within this time, the specimen must be correctly inserted, the safety door closed, and the test performed. Short distances, insertion aids, and a start button within easy reach support the manual test procedure.
Automation also increases process reliability: It moves the specimen reproducibly into the test position, reduces operator influence, and helps ensure compliance with the specified time window, especially when testing large numbers of specimens.
Selecting the pendulum impact tester
For tests in accordance with ISO 148, ZwickRoell offers the pendulum impact testers HIT300P, HIT450P, and HIT750P in its testing portfolio. It is essential that the pendulum is suitable for the expected impact energy and meets the requirements of the standard. ISO 148-1 specifies an upper limit of 80% of the pendulum capacity, but no lower limit. Accordingly, a HIT450P with a 450-joule pendulum hammer can be used for standards-compliant testing in the range from 0 to 360 joules.
Selecting the impact fixture
For the HIT300P and HIT450P pendulum impact testers, ZwickRoell offers two impact fixture variants: the Charpy impact fixture and the universal impact fixture.
The Charpy impact fixture is specifically designed for Charpy tests. Its anvils can be rotated and also switched from one side to the other. This allows the anvils to be used in four positions before they need to be replaced. Therefore, the need for replacement due to wear in everyday laboratory use is reduced.
The universal impact fixture offers greater flexibility in terms of test types. If required, it can be converted for Izod tests or tensile impact tests, for example. It is therefore particularly suitable for laboratories that need to perform different test methods using a single pendulum impact tester.
On the HIT750P pendulum impact tester, the supports and anvils are mounted directly in the instrument, so a separate impact fixture is not required. It is primarily suitable for Charpy tests, but tensile impact tests are also possible.
Accounting for energy losses
Friction and air resistance are always present in pendulum impact testers. ZwickRoell instruments allow these effects to be determined so that they can be compensated for, provided the test setup remains unchanged. This allows the measured energy absorption to be attributed more accurately to the specimen rather than to the testing system.
Automated Charpy impact testing to ISO 148-1
Automation is particularly beneficial for ISO 148 testing when large numbers of specimens are being tested, when testing is performed at controlled temperatures, or when operator influence needs to be minimized. Automated testing systems reliably maintain the maximum 5-second time window between removal from temperature conditioning and the impact test.
The automated testing system roboTest I can automatically test up to 450 notched metal specimens in a temperature range of -180°C to +300°C.
ZwickRoell offers various configurations designed to work with the respective pendulum impact tester:
- A semi-automated version of the HIT450P is available, in which the operator places the specimens in the temperature-conditioning equipment and then initiates the test under controlled conditions.
- For the HIT750P, both semi-automated and fully automated solutions are available. With the fully automated version, the user simply fills the magazine. Once the system has been started, the specimens are fed into the system, brought to the specified temperature, tested after a defined conditioning period, and then discharged from the test area via an optional conveyor.
For all robotic testing systems, the autoEdition3 automation software is used for information input and control.
Additional options are available as needed:
- ID code scanner for mapping specimens, batches, production slots, and results
- Optional dimensional measurement, specifically notch depth or remaining height
- Magazines for up to 600 specimens
- Poka-Yoke-based specimen holder for proper notch alignment
- Cleaning of the anvils after the test
- IntelliDrive for automated pendulum height adjustment under varying test conditions.
- Extended temperature range up to +600°C
- Discharge conveyor and optional sorting of specimen remains
This makes automation suitable not only for temperature-controlled tests, but also for laboratories with high specimen throughput and standardized test procedures.
Typical applications of ISO 148-1
ISO 148 is used in all applications where the behavior of metallic materials under impact loading, at low temperatures, or during the brittle-ductile transition must be evaluated.
Typical use cases:
- Quality assurance for metallic materials: Verification that materials meet specifications and that test results remain comparable.
- Steel mills and foundries: Determination of material properties for data sheets, customer approvals, and quality control.
- Materials development and design: Selection of suitable materials for components that must operate safely at specific ambient temperatures.
- Evaluation of brittle fracture behavior: Evaluation of the temperature at which a material transitions to more brittle or more ductile fracture behavior.
- Calibration and accreditation bodies: Inspection of equipment, testing processes, and laboratories.
- Research, education, and universities: Teaching fundamental materials testing methods and investigating the fracture behavior of metallic materials.
ISO 148-1 with testXpert testing software
The testXpert testing software supports ISO 148 testing through predefined test sequences, standardized settings, and traceable documentation that includes standard test programs and master test programs. Depending on the configuration, testXpert can be used directly on the device via a digital display or through a PC. PC connectivity is particularly relevant when results need to be documented in greater detail, processed further, or transferred to existing data structures.
Functional benefits for laboratories:
- Less operator influence due to standardized test procedures
- Traceable recording of test parameters and results
- Consistent evaluation of recurring tests
- Better documentation for quality assurance, accreditation, and customer reports
- Interoperability with digital laboratory and data processes
Frequently asked questions about ISO 148
ISO 148 describes the Charpy impact test on notched metal specimens. The test is used to determine the impact energy absorbed by the material and to evaluate its fracture behavior, particularly its brittle and ductile components.
The key parameter is the absorbed impact energy in joules. In addition, the percentage of brittle fracture can be determined based on the fracture surface. According to the interview, in practice, this percentage is assessed manually or visually based on the fracture surface.
Typical causes include non-compliant specimen dimensions, defective notches, off-center notch positioning, surface defects, incorrect specimen placement, insufficient temperature conditioning, exceeding the time window between temperature conditioning and impact testing, as well as improperly configured or incorrectly calibrated test equipment.
Tests in accordance with ISO 148 can be performed using the ZwickRoell HIT300P, HIT450P, and HIT750P pendulum impact testers.
No. The HIT50P pendulum impact tester does not reach the impact velocity of 5 to 5.5 m/s required by ISO 148.
No, generally not. ISO 148 specifies only an upper limit: The impact energy absorbed must not exceed 80% of the pendulum capacity. The standard does not specify a lower limit.
With the HIT450P, which has a pendulum capacity of 450 J, impact energies ranging from 0 to 360 J can thus be tested.
At very low impact energies, however, the determined friction must be taken into account. If the friction energy is of the same order of magnitude as the impact energy measured on the specimen, or even exceeds it, this can impair the validity of the result. In this case, a smaller pendulum hammer is the appropriate choice.
If the same specimen geometry must be used, a larger pendulum is required. Alternatively, subsize specimens with a smaller thickness can be used, such as 7.5 mm, 5 mm, or 2.5 mm. Shims are available for these thicknesses to ensure that the pendulum strikes the specimen at its center.
Metallic materials can exhibit more brittle fracture behavior at low temperatures. Therefore, the specimen must be conditioned to a uniform temperature throughout and tested very quickly after removal from the temperature-conditioning environment. ISO 148 specifies a time window of 5 or 10 seconds, depending on the temperature difference from the ambient environment.
V-notches and U-notches have different geometries and produce a different stress concentration at the notch. This causes the measured results to differ.
Automation is particularly beneficial for temperature-controlled tests, tight time frames, high specimen volumes, or when operator influence needs to be reduced. It provides more consistent test procedures, reproducible specimen insertion, and reliable compliance with the specified time between temperature conditioning and impact.
