Room temperature cantilever beam notched impact testing, commonly known as the notched Izod impact test, is a standardized pendulum impact method used to quantify the toughness and notch sensitivity of plastic materials under ambient laboratory conditions. Conducted in accordance with internationally recognized standards such as ISO 180, ASTM D256, and GB/T 1843, this test measures the energy absorbed by a notched specimen when fractured by a single pendulum strike, and it is widely applied in quality control, material qualification, and product development across the plastics and composites industries.
Technical Overview
Room temperature cantilefer beam notched impact testing refers to the determination of the impact resistance of plastics using a notched specimen supported as a vertical cantilever beam and struck by a freely swinging pendulum. This configuration is universally known as the Izod impact test. A precisely machined notch is placed on the face of the specimen facing the striker, creating a controlled stress concentration. When the pendulum is released, it fractures the specimen at the notch plane, and the difference between the initial and residual pendulum energies represents the energy absorbed by the material during fracture.
The test is performed in a conditioned laboratory atmosphere, typically 23 °C ± 2 °C and 50 % ± 5 % relative humidity, which is defined as the standard room temperature condition for plastics testing. The absorbed energy is normalized by the cross-sectional area of the specimen at the notch root and reported as notched Izod impact strength in kJ/m². Because the presence of a sharp notch promotes brittle, crack-initiation-controlled failure, the method is particularly effective for evaluating notch sensitivity, comparing material ductility, and assessing the influence of additives, fillers, processing conditions, and environmental exposure on fracture behavior.
The principal governing standards include:
- ISO 180 – Plastics – Determination of Izod impact strength
- ASTM D256 – Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics
- GB/T 1843 – Chinese national standard for the determination of Izod impact strength of plastics
- JIS K 7110 – Japanese industrial standard for Izod impact strength of plastics
Test results obtained by accredited third-party laboratories following these standards are widely accepted for material datasheets, supplier certifications, regulatory compliance, and design verification.
Testing Samples
Standard Molded Specimens
The preferred specimen geometry per ISO 180 and GB/T 1843 is 80 mm in length, 10 mm in width, and 4 mm in thickness, with a machined notch of 2 mm depth located at the midpoint of the specimen length. Under ASTM D256, the typical specimen measures 63.5 mm × 12.7 mm × 3.2 mm (or 6.4 mm thickness, depending on material availability). Specimens are generally produced by injection molding directly to final dimensions to minimize machining-induced stresses.
Specimens Machined from Products
When testing finished or semi-finished products such as sheets, plates, pipes, fittings, profiles, or molded parts, specimens may be cut and machined from the actual article. This approach provides impact data representative of the real component, including the effects of processing history, orientation, and service exposure. Machined specimens must be prepared carefully to avoid heating, residual stress, or surface damage that could distort the measured impact strength.
Notch Types
ISO 180 and GB/T 1843 define three standard notch geometries, distinguished by the radius of the notch root:
- Type A notch: root radius 0.25 mm, the most commonly used geometry for general comparison
- Type B notch: root radius 1.0 mm, used for materials that are too brittle with Type A notching or for specific comparative programs
- Type C notch: root radius 0.1 mm, used for highly notch-insensitive or tough materials
Notch quality is a dominant factor in result validity. Notches must be cut with a sharp, profiled cutter at controlled feed rates, and cutter sharpness must be verified regularly, as a dull cutter raises the measured impact strength artificially.
Conditioning
All specimens must be conditioned prior to testing in a standard atmosphere of 23 °C ± 2 °C and 50 % ± 5 % relative humidity in accordance with ISO 291 or ASTM D618. Typical conditioning durations range from a minimum of 16 hours up to 88 hours depending on specimen thickness, ensuring that moisture content and temperature are equilibrated so that results are reproducible.
Testing Items
The primary deliverables of a room temperature cantilever beam notched impact test program include:
- Notched Izod impact strength (kJ/m²) determined per ISO 180, GB/T 1843, or JIS K 7110
- Izod impact resistance (J/m of notch width, or ft·lb/in) determined per ASTM D256
- Total energy absorbed during fracture (J) for each specimen
- Statistical summary of results, including mean value, standard deviation, and coefficient of variation
- Failure behavior classification for each specimen
Specimen failure modes are classified per ISO 180 as complete break (C), hinge break (H), partial break (P), or non-break (NB). This classification is essential because impact strength values obtained from partial or non-breaking specimens are not directly comparable with those from complete breaks, and they must be reported with the appropriate designation.
Testing Methods
The test procedure follows a well-defined sequence to ensure accuracy and comparability:
- Verify instrument calibration and the friction losses of the pendulum apparatus before testing.
- Condition the specimens at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for the required period.
- Measure the width and thickness of each specimen at the notch plane with a calibrated micrometer to determine the net cross-sectional area.
- Select a pendulum capacity such that the absorbed energy falls between 10 % and 80 % of the nominal pendulum energy, which guarantees measurement accuracy.
- Clamp the specimen vertically in the vise as a cantilever, with the notch facing the pendulum striker and the notch plane aligned with the top of the clamping jaws.
- Release the pendulum from its raised position, allowing it to strike and fracture the specimen at an impact velocity of approximately 3.5 m/s.
- Record the absorbed energy from the instrument indicator, correct for air friction and windage where required, and classify the observed failure mode.
- Calculate the notched impact strength by dividing the corrected absorbed energy by the cross-sectional area at the notch, and test a minimum of five, preferably ten, specimens per condition.
For materials exhibiting large spreading of results, or when comparing formulations, a larger sample population improves statistical confidence. All test conditions, including notch type, pendulum capacity, specimen preparation method, and failure classifications, must be documented in the final test report in full accordance with the requirements of the applicable standard.
Applications
Room temperature cantilever beam notched impact testing is one of the most widely executed mechanical tests in the plastics industry and supports a broad range of engineering and commercial activities:
- Material characterization and datasheet generation for thermoplastics such as ABS, PP, PE, PC, PA, POM, PVC, PMMA, PBT, and their modified grades
- Evaluation of thermosetting molding compounds and fiber-reinforced polymer composites
- Quality control and incoming material inspection at manufacturing facilities
- Comparison of impact modifiers, fillers, reinforcements, and recycled content on toughness
- Automotive interior and exterior components, where impact safety and ductility at ambient conditions are required
- Electrical and electronic equipment housings and enclosures subject to mechanical abuse testing
- Pipes, valves, and fittings for pressure and drainage systems
- Household appliance components, consumer goods, and packaging materials
- Research and development programs, formulation optimization, and failure analysis investigations
- Compliance verification for product certifications where accredited third-party laboratories provide test reports referenced to ISO 180 or ASTM D256
In many specifications, room temperature Izod data are complemented by sub-ambient testing to construct ductile-to-brittle transition curves, giving designers a complete picture of impact performance across the expected service temperature range.
FAQ
What is the difference between the Izod and Charpy impact tests?
In the Izod (cantilever beam) configuration, the notched specimen is clamped vertically at one end and struck as a cantilever, with the notch facing the striker. In the Charpy (simply supported beam) configuration, the specimen lies horizontally on two supports and is struck at midspan opposite the notch. The two methods are governed by different standards (ISO 180 and ASTM D256 for Izod; ISO 179 and ASTM D6110 for Charpy), use different specimen support conditions, and produce results that are not directly interchangeable.
What temperature defines room temperature for this test?
Room temperature corresponds to the standard laboratory atmosphere of 23 °C ± 2 °C with 50 % ± 5 % relative humidity as defined in ISO 291 or ASTM D618. Specimens must be conditioned to equilibrium in this atmosphere before testing, and the test itself should be carried out under the same conditions.
Why is a notch machined into the specimen?
The notch creates a controlled, three-dimensional stress concentration that promotes crack initiation at a known location and ensures reproducible, crack-propagation-dominated failure. This allows the test to measure the material resistance to brittle crack growth and to reveal notch sensitivity that would be masked in unnotched testing.
What units are used for reporting the results?
ISO 180, GB/T 1843, and JIS K 7110 report notched Izod impact strength in kJ/m², calculated as absorbed energy divided by the cross-sectional area at the notch. ASTM D256 reports impact resistance in J/m of notch width or ft·lb/in of notch width. Because the normalization bases differ, ISO and ASTM values cannot be compared directly without conversion and verification.
How many specimens should be tested?
A minimum of five specimens is generally required, with ten specimens recommended for most materials to provide statistically meaningful mean values and scatter information. Additional specimens are advisable for materials showing mixed failure modes such as partial break or non-break.
What precautions ensure valid and comparable results?
Key precautions include using a sharp, freshly verified notching cutter, conditioning specimens to the standard atmosphere, selecting a pendulum whose capacity keeps the absorbed energy between 10 % and 80 % of nominal energy, correctly aligning the notch with the striker and clamping plane, and performing the test on a regularly calibrated instrument operated by trained personnel in accredited third-party laboratories or qualified in-house facilities.