ASTM E23: notched bar impact testing of metallic materials, Charpy & Izod
ASTM E23 specifies notched impact tests on metallic materials and covers Charpy and Izod tests on notched specimens. In practice, variations often arise from specimen preparation, notch quality, temperature control, specimen positioning, pendulum selection, and verification of the test setup. ZwickRoell helps laboratories control these variables by providing appropriate testing equipment, insertion aids, temperature conditioning solutions, testXpert testing software, and automation.
A further description of the Charpy pendulum impact test on notched bar metal specimens can be found in the ISO 148-1 standard.
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ASTM E23 – Key facts at a glance
- ASTM E23 is used for notched impact tests on metallic materials and, unlike ISO 148, covers both Charpy and Izod tests.
- The test is sensitive to specimen geometry, notch depth, notch location, surface quality, and material inhomogeneity. Even small deviations can alter the measured impact energy.
- In temperature-controlled tests, the time between removal from the temperature-conditioned environment and the impact test determines the validity of the results.
- Charpy and Izod results are not directly comparable because the specimen is subjected to different types of stress.
- ASTM E23 specifies requirements for the direct and indirect verification of the pendulum impact tester.
- ZwickRoell reduces typical operator influences through the use of appropriate pendulum impact testers, insertion aids, temperature-controlled procedures, testXpert test programs, and automation for Charpy tests.
ASTM E23 in practice: Common sources of error and their effect on test results
At first glance, the test procedure a notched bar impact test seems simple: Insert the specimen, release the pendulum, and determine the impact energy. In practice, however, the comparability of the results depends on many details. Of particular concern are any steps that affect the notching effect, the temperature of the specimen, its position at the center of impact, or the pendulum's energy loss.
Typical causes of variation include:
- Non-compliant specimen dimensions:Standard Charpy specimens measure 10 × 10 × 55 mm. Deviations in length, width, height, or residual cross-section change the bending stress and make it difficult to compare results with reference values or those from other laboratories.
- Incorrect notch geometry: Notch depth, notch radius, and notch shape affect local stress concentration. If the notch depth is too shallow, it can result in higher impact energy values; if the notch is too deep, it can result in lower values.
- Incorrect notch position:In Charpy specimens, the notch is centered; in Izod specimens, it is off-center. If the notch is positioned incorrectly or if a Charpy specimen is treated like an Izod specimen, the result is not reliable.
- V-notches and U-notches are often confused: Different notch shapes should not be compared directly with one another. The notch geometry determines the fracture behavior and must be compatible with the selected method and analysis.
- Poor notch or surface quality: Scratches, burrs, or damaged surfaces can affect crack propagation. In addition, rough or damaged specimens can subject the supports to greater wear and affect subsequent measurements.
- Off-center positioning in the Charpy test: The specimen must be positioned so that the pendulum hammer strikes the side opposite the notch. If the specimen is not centered, the loading is shifted and the measured impact energy can deviate significantly.
- Improper clamping for Izod: In the Izod test, the specimen is clamped at one end. Differences in clamping force or non-reproducible clamping alter the boundary conditions and thus the fracture behavior.
- Insufficient temperature control: At low temperatures, many metals become more brittle. If the specimen is not conditioned to a uniform temperature throughout, the result may not reliably reflect the actual test temperature.
- Excessive time between removal and impact: When there are larger temperature differences between the specimen and the ambient environment, there is only a very short time window in which to perform the test. Any delay increases the risk that the specimen will no longer be at the intended temperature.
- Tongs not conditioned to the same temperature:If a cooled specimen is handled with warm tongs, heat can be introduced locally. This is particularly critical in tests conducted near the transition temperature between ductile and brittle behavior.
- Incorrect pendulum selection: ASTM E23 specifies an upper limit of 80% of the pendulum capacity, as well as a lower limit based on the measurement resolution (25 times the highest resolution of the instrument; with our digital display resolution of 0.1 J, this corresponds to a lower limit of 2.5 joules). An unsuitable measurement range can adversely affect the accuracy and validity of the results.
- Insufficiently verified test setup: ASTM E23 covers both direct and indirect verification. Support span, radii, striker, reference specimens, and instrument behavior must be verifiably checked; otherwise, systematic deviations may go undetected.
- Wear or residue on the anvils: Worn anvils, fragments, or wear debris can alter the support conditions. This is particularly relevant in series testing if residues are not removed promptly.
Would you like to perform ASTM E23 tests with greater reproducibility or ensure the reliability of an existing testing solution?
Your local ZwickRoell expert can assist you in selecting the pendulum impact tester, impact fixture, pendulum hammer, temperature-conditioning solution, software, and level of automation to suit your material, standard requirements, and testing volume.
Performing the notched impact test to ASTM E23 with ZwickRoell
Critical test steps and ZwickRoell testing solutions explained in detail:
Temperature Control Specimen Positioning Pendulum Tester Selection Pendulum Hammer Selection Impact Fixture & Anvil Selection Verification Energy Losses Automation Options
Here’s how the test works:
In the notched impact test according to ASTM E23, a notched metal specimen is subjected to an impact loadusing a pendulum hammer. The standard covers Charpy and Izod tests.
- In the Charpy method, the specimen rests on two supports and the impact is applied opposite the notch.
- In the Izod test, the specimen is clamped on one side and struck while upright.
Before the test, the specimen dimensions, notch geometry, temperature, and the appropriate pendulum hammer are determined. After being released, the pendulum strikes through or breaks the specimen. The absorbed impact energy in joules is determined from the difference between the initial height and the rise height. In addition, the fracture characteristics can be evaluated, such as the proportion of brittle fractures.
For temperature-dependent material evaluations, specimens are tested at room temperature, lower temperatures, or elevated temperatures to assess the transition behavior between ductile and brittle fracture.
Temperature control: A few seconds can make the difference when it comes to comparability
Many metallic materials exhibit changes in their fracture behavior as temperature varies. At low temperatures, they tend to fracture in a more brittle manner, while at room temperature or higher temperatures, they tend to exhibit more ductile behavior. For this reason, the ASTM E23 test is frequently used to evaluate transition temperatures or the percentage of brittle fracture.
The time between removing the specimen from the temperature-conditioning environment and performing the impact test is particularly critical. If the specimen is inserted too slowly or warms up during handling, the result no longer reliably reflects the intended test temperature.
For manual tests, ZwickRoell provides temperature-conditioned insertion tongs to prevent unwanted heat transfer when gripping the specimen. In addition, the temperature-conditioning equipment is positioned close to the pendulum impact tester, allowing for a rapid test procedure.
The insertion tongs grip the specimen at the notch and, with their centering function, enable quick and precise positioning in the impact fixture. For automated Charpy tests, the specimen feeding system ensures compliance with the specified time window between leaving the temperature-conditioning environment and the impact test. This reduces operator influence and increases reproducibility, especially during temperature-controlled tests.
Specimen positioning: Small positioning errors alter the impact stress
In the Charpy test, the specimen must be positioned precisely so that the pendulum strikes opposite the notch . Even a lateral shift means that the notch, line of impact, and anvils no longer interact under ideal conditions.
During manual testing, the repeatability depends heavily on the operator's experience, handling, and insertion speed. This is particularly true for cooled specimens, where the specified time limit must also be met.
Insertion aids such as tongs with a suitable notch holder, stops, or positioning aids make it easier to center the specimen. With automated Charpy systems, the feeding process is reproducible. As a result, not only is the time between temperature conditioning and impact controlled, but the specimen position in the test setup is also standardized.
ZwickRoell pendulum impact testers for ASTM E23
For tests conducted in accordance with ASTM E23, various pendulum impact testers from the HIT series are used, depending on energy requirements, test method, test volume, and degree of automation. What matters is not only the maximum pendulum capacity, but the complete test setup consisting of the pendulum hammer, impact fixture, anvils, striker, protective enclosure, software, and optional automation.
HIT50P – Compact solution for low impact energies according to ASTM E23
For Charpytests according to ASTM E23 with low energy absorption , the HIT50P can be a space-saving and economical solution. This is particularly relevant for laboratories that perform tests in accordance with ASTM E23 but do not require high impact energies or have limited space for a large pendulum impact tester.The HIT50P is particularly suitable when the expected energy values fall within the permissible measurement range. For a 50 J pendulum, the ASTM E23 upper limit of 80% of the pendulum's energy can mean that tests up to 40 J can be covered. This makes the HIT50P particularly suitable for more brittle metallic materials or applications with lower energy absorption.
HIT300P / HIT450P – Flexible for Charpy & Izod
The HIT300P/HIT450P is designed for impact testing of metal specimens and is suitable for Charpy and Izod tests in accordance with ASTM E23.
For Charpy tests, semi-automatic specimen centering ensures precise alignment of the specimen at the notch. The specimen is positioned reproducibly; when the test is triggered, the centering device automatically moves out of the test area. This prevents the specimen from shifting when the safety door closes or from being positioned incorrectly in relation to the line of impact..For laboratories with varying testing requirements, the universal impact tester is a flexible solution, as it allows for both Charpy and Izod tests. If Charpy tests are performed exclusively or predominantly, a special Charpy impact fixture may be useful, especially when the test volume is high.
HIT750P – High impact energies for Charpy tests
The HIT750P is designed for notched bar impact tests on Charpymetal specimens with high energy requirements . With a rated working energy of 750 J, a drop height of 1,500 mm, and an impact velocity of 5.42 m/s, the HIT750P is capable of handling demanding test tasks. Pendulum hammers with energy levels of 300 J, 450 J, 600 J, and 750 J are available, allowing for adaptation to different materials and expected energy absorption.In practical testing, the HIT750P is particularly relevant when tougher materials or high impact energies need to be tested reliably. Automatic pendulum lifting, electromagnetic pendulum release, rapid specimen feeding for temperature-conditioned specimens, and electronic and analog result displays support a stable and traceable test procedure.
Another advantage is the software-based consideration of air resistance for air and bearing friction. This excludes energy losses not caused by the specimen from the evaluation of the results. As a result, systematic deviations are reduced and the comparability of the measured values is improved.
Pendulum hammer and measurement range: The energy must be appropriate for the material
ASTM E23 specifies a permissible operating range for the pendulum. The upper limit is 80% of the pendulum capacity. Unlike ISO 148, ASTM E23 also specifies a lower limit that depends on the highest resolution of the instrument. Therefore, the pendulum hammer must not only be large enough, but must also be appropriate for the expected energy absorption.
For more brittle materials, a smaller pendulum may be sufficient. For tougher materials, a higher working capacity is required. If this range is exceeded, a larger pendulum or a different specimen geometry must be used.
ZwickRoell pendulum impact testers in the HIT series can be configured to meet various energy requirements. For ASTM E23, the HIT50P can be a compact solution for low impact energies. For higher energies, larger pendulum impact testers with capacities of 450 joules or 750 joules are an option. The selection should be based on preliminary tests, material behavior, expected impact energy, and standard requirements.
Impact fixture, anvils, and striker: Critical for consistent results
For reproducible notched bar impact bending tests in accordance with ASTM E23, selecting the right pendulum hammer is not the only critical factor. The support span, anvil geometry, and condition of the striker directly affect the stress on the specimen. Wear, residue, or damaged support surfaces can distort the results. Therefore, the anvils and strikers should be inspected regularly and replaced as necessary.
The support span and anvil geometry have a direct effect on the bending stress on the specimen. If the support span is too large, the specimen can be fractured more easily. If it is too small, higher impact energy values may result. Worn, damaged, or dirty anvils, as well as a worn striker, also alter the support and force application conditions.
A ZwickRoell Charpy impact fixture can be used for Charpy tests. The anvils can be rotated and switched from one side to the other, allowing them to be used multiple times. This extends their service life and reduces the need for replacement parts. If other types of tests, such as the Izod test, are planned in addition to the Charpy test, a universal impact fixture offers additional flexibility.
The installation of the pendulum impact tester is also important. A sufficiently solid and stable base reduces vibrations and unwanted energy losses. This ensures that the energy measured during the test is attributed as clearly as possible to the specimen's fracture behavior.
Direct and indirect verification: ASTM E23 requires more than just a measurement
ASTM E23 covers the verification of the pendulum impact tester. During direct verification, measurable parameters such as support span, anvil radii, and striker geometry are checked. During indirect verification, reference specimens are impact tested to determine whether the expected results are within the permissible tolerances.
If the indirect verification is not within tolerance, this indicates deviations in the test setup, wear, or a condition of the equipment that requires further investigation.
ZwickRoell supports laboratories with pendulum impact testers that comply with standards, test setups that can be calibrated and verified, as well as service and consulting expertise. For reproducible ASTM E23 tests, it is not only the pendulum that is crucial, but the entire setup, including the impact fixture, striker, anvils, measuring system, software, and regular inspections.
Friction, air resistance, and energy losses: Avoiding systematic deviations
In pendulum testers, there are unavoidable losses due to friction and air resistance. If they are not taken into account, energy losses will be included in the test results even though they were not caused by the material.
ZwickRoell pendulum impact testers enable the determination of friction and air resistance. If the test setup remains unchanged, these losses can be taken into account and compensated for in the measured results. This increases the validity of the impact energy measurement and reduces systematic deviations.
Automated notched bar impact tests to ASTM E23
Automation is particularly beneficial for ASTM E23 when Charpy tests are performed at controlled temperatures, with high specimen throughput, or when operator influence is to be minimized. The most critical point is often not the notched impact test itself, but the procedure leading up to it: Temperature conditioning, removal, positioning, closing the safety device, and triggering the test must be performed reproducibly and within the specified time window.
The robotic testing system roboTest I enables the automated performance of Charpy impact tests on notched metal specimens. The system handles temperature control, specimen transport, positioning, and test initiation. This reduces the impact of human factors such as hand temperature, moisture, off-center placement, or delayed test initiation.
This is especially important for temperature-controlled tests. The specimen must be tested within a few seconds after leaving the temperature-conditioning environment to ensure that the actual test temperature is maintained. Automation supports precisely this step: The test procedure is standardized, the time between temperature conditioning and impact is monitored, and the specimen is positioned reproducibly.
For laboratories with a large number of specimens, automation also offers an efficiency advantage. Rather than inserting and triggering each specimen individually, the operator can process recurring series tests in a much more standardized manner. This reduces the workload for laboratory personnel while also improving the comparability of the results.
- Semi-automatic Charpy test
A semi-automatic version is available for the HIT450P. The operator inserts the specimens one at a time into the temperature conditioning equipment. The specimens are brought to the specified temperature, including the holding time. As soon as a specimen is ready for testing, a signal notifies the operator, who triggers the test for each specimen at the push of a button.
The primary benefit lies in process reliability: The specimen is removed from the temperature-conditioning environment and tested within the required time window. At the same time, the operator remains involved in the process but does not have to perform critical steps entirely manually. - Fully automatic Charpy test
For the HIT450P and HIT750P pendulum impact testers, ZwickRoell offers a fully automated version with magazine towers. For standard specimens with a 10 × 10 mm cross-section, a single magazine tower can hold up to 45 specimens. Multiple magazine towers can be integrated into the system. The specimens are stored, automatically fed into the temperature conditioning environment, brought to the correct temperature, tested, and then transported out of the system via an optional discharge conveyor.
If desired, specimen remains can be sorted, specimens can be identified by ID code, incorrectly read specimens can be ejected, dimensions can be measured, or the anvils can be cleaned after each test. For varying pendulum heights, IntelliDrive can automate pendulum height adjustment.
Do you regularly test temperature-conditioned Charpy specimens or high specimen volumes to ASTM E23?
Automated ZwickRoell testing systems standardize temperature control, material feeding, positioning, and result assignment. This reduces operator influence, ensures compliance with the specified time window between temperature conditioning and impact, and reduces the workload for laboratory personnel during recurring series tests.
Typical applications for ASTM E23
ASTM E23 is used wherever metallic materials must be evaluated with regard to their behavior under impact loading.
Typical applications include:
- Quality assurance in metal production: Steel mills, foundries, and manufacturers of metallic materials test whether material properties meet specifications.
- Verification of material properties for customers: Notched bar impact test results can be used in data sheets, test reports, or approval processes.
- Material selection in design and development: The test helps determine whether a material is suitable for an application involving specific temperature or impact loads.
- Evaluation of brittle fracture behavior: Particularly at low temperatures, the test helps determine the transition between ductile and brittle fracture behavior.
- Comparison of batches and manufacturing processes: Test results can indicate whether material behavior varies between batches, heat treatments, or manufacturing processes.
- Calibration and accreditation: Testing laboratories and accreditation bodies use this method to ensure the reliability of testing systems, procedures, and comparability.
- Research and education: ASTM E23 testing reveals fundamental relationships between notch effect, temperature, and fracture behavior.
ASTM E23 with testXpert testing software – Efficient and reliable testing
The testXpert testing software supports the notched bar impact test in accordance with ASTM E23 in applications where reproducible procedures, traceable parameters, and reliable result assignment are critical. Test parameters can be stored in predefined test programs . This standardizes test procedures and reduces operator influence.
The software can be used with the pendulum impact tester as a standalone solution via a digital display or connected to a PC. For laboratories with simple procedures, the display on the instrument itself may be sufficient. For larger amounts of data, analyses, reports, or integrations with existing systems, the PC connection offers added convenience.
One functional benefit is the clear assignment of test results, specimen information, and test parameters. In automated systems, the software can also interact with an ID code scanner, dimension measurement, the temperature-conditioning procedure, and results management. This facilitates standards-compliant documentation, reduces data transfer errors, and supports comparable test results across test series.
Frequently asked questions regarding ASTM E23
ASTM E23 testing is used to determine the impact energy and evaluate the impact toughness of metallic materials. It shows how a metal responds to impact loading and whether it exhibits more ductile or brittle behavior. This test is particularly relevant for the evaluation of brittle fracture behavior and for comparing materials at different temperatures.
The key measurement is the impact energy absorbed in joules. In addition, the fracture characteristics can be evaluated, such as the percentage of brittle fracture. This evaluation is based on the fracture surface.
The testing principles are similar in many respects, particularly in Charpy tests on notched metal specimens. One important difference is that ASTM E23 includes Izod tests in addition to Charpy tests. In addition, the verification of the test equipment is included directly in ASTM E23, whereas in ISO 148 it is addressed in additional parts of the standard.
Unnotched specimens can be tested using appropriate equipment; however, in this context, they would not be part of standards-compliant testing per ASTM E23.
In the Charpy test, the specimen rests on two supports and is struck opposite the notch. In the Izod test, the specimen is clamped on one side and struck while upright. The results of the two methods are therefore not directly comparable.
The selection depends on the type of loading that is to be represented in the subsequent application. Charpy uses a supported specimen subjected to impact bending. Izod uses a specimen clamped at one end. The test method must therefore be appropriate for the question being investigated and the behavior of the component.
Typical standard Charpy specimens are 55 mm long, 10 mm wide, and 10 mm thick. The notch is in the center of the specimen. Depending on the method, V-notches, U-notches, or keyhole notches may be used.
For V-notches, the notch depth, notch radius, and remaining width at the base of the notch are particularly important because they determine the stress concentration at the notch. For U-notches, the larger radius changes the fracture behavior. Therefore, different notch shapes should not be compared directly with one another.
Typical Izod standard specimens are 75 mm long, 10 mm wide, and 10 mm thick. The notch is located off-center, 28 mm from the top of the specimen.
Izod specimens differ from Charpy specimens primarily in terms of the notch position and the type of loading. The specimen is clamped at one end rather than placed on two supports, as in the Charpy method.
These differences are crucial for the analysis. Charpy and Izod results are not directly comparable because the test setups, force application, and fracture mechanics differ.
The notch creates the stress concentrationat which the fracture initiates. Notch depth, notch shape, notch radius, position, and surface quality therefore directly influence the measured impact energy and the fracture behavior.
If standard specimens cannot be used due to the material, component geometry, or amount of specimen material available, smaller specimen geometries—known as subsize specimens—can be used. In such cases, special supports are used to ensure that the height of the specimen is properly aligned with the pendulum.
The actual specimen dimensions must also be documented and taken into account during the evaluation. This is particularly important because smaller specimens may exhibit different energy absorption patterns than standard specimens. Results from standard and subsize specimens should therefore not be compared without context.
Many metals become more brittleat low temperatures. Notched-bar impact tests are therefore frequently performed at different temperatures to evaluate the transition between ductile and brittle fracture behavior.
If too much time elapses between removing the specimen from the temperature-conditioning environment and testing it, the specimen temperature changes. This can lead to variations , particularly during tests below room temperature or near the transition temperature.
Izod tests are generally performed at room temperature. The reason lies in the test setup: The specimen is clamped at one end, and the clamping arrangement is often part of the pendulum impact tester. As a result, the entire clamping environment cannot be temperature-conditioned in the same way as with Charpy specimens.
For temperature-controlled notched bar impact tests, the Charpy method is therefore the more suitable method in many cases. The specimen can be temperature-conditioned, inserted quickly, and tested within the required time window.
The pendulum must be appropriate for the expected energy absorption. ASTM E23 specifies an upper limit of 80% of the pendulum capacity and also a lower limit based on the measurement resolution (25 times the highest resolution of the instrument; with a resolution of 0.1 joule on our digital display, this corresponds to a lower limit of 2.5 joules). An unsuitable measurement range can impair the validity of the results.
Yes, for lower energy ranges, the HIT50P (50 joules) can be a suitable solution, especially when only low impact energies are expected or when laboratory space is limited. This smaller pendulum impact tester is not suitable for tests in accordance with ISO 148, because it does not achieve the impact velocity required by that standard.
The ZwickRoell roboTest I automation solution provided is designed for Charpy tests on metal specimens. It combines specimen feeding, temperature conditioning, holding time, positioning, and testing. Depending on the system, semi-automated or fully automated test procedures are possible.
The testXpert testing software supports standardized test programs, traceable test parameters, result assignment, and documentation. In automated systems, additional functions such as ID code recognition, dimensional measurement, and results management can be integrated.
