ASTM D256 Izod Impact Testing of Plastics
ASTM D256 is a standard test method that measures the resistance of plastic materials to breakage by flexural properties. The test involves striking a specimen with a pendulum-type hammer, then measuring the energy required to break it. This standard is commonly used to determine the impact strength of thermoplastic materials.
TRUSTED BY
ASTM D256 Izod Impact Testing of Plastics
- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
ASTM D256 Izod Impact Testing of Plastics Overview
ASTM D256 is the standard test method for determining the impact resistance of plastics using notched and unnotched specimens in both the Izod (cantilever beam) and Charpy (simple beam) configurations. Impact resistance is the ability of a material to absorb energy from a sudden load without fracturing -a property distinct from strength or stiffness that predicts how a plastic part will behave when it is struck, dropped, or subjected to a sudden impact load in service.
The test uses a pendulum hammer that swings and strikes a notched specimen. For the Izod test, the specimen is clamped vertically as a cantilever and struck near its free end. For the Charpy test, the specimen is supported horizontally at both ends and struck at the center. The energy absorbed during fracture is read from the pendulum’s loss of momentum. The notch in the specimen acts as a stress concentrator that forces fracture initiation at a defined location, making results reproducible and comparable across materials and labs.
The notch geometry matters significantly in D256 testing. A sharper notch gives lower impact values because it provides a more severe stress concentration. ASTM D256 specifies the standard notch radius, but also allows testing with different notch radii and unnotched specimens. Many materials show dramatically different impact behavior depending on the notch radius -a phenomenon called notch sensitivity -and understanding that behavior is often as important as the absolute impact value.
ASTM D256 Izod Impact Testing of Plastics Scope, Applications, and Benefits
Scope
ASTM D256 covers notched Izod impact testing (Method A), notched Charpy impact testing (Method B), unnotched Izod testing (Method C), reversed notched Izod testing (Method D), and tensile impact testing (Method E) for rigid plastics. The standard notch is 0.25 mm radius for Methods A through D. Specimens are rectangular bars, typically 63.5 mm x 12.7 mm x varying thickness for Izod, and 127 mm x 12.7 mm for Charpy. Conditioning at 23 plus or minus 2 degrees C and 50 plus or minus 10 percent RH for minimum 40 hours is required before testing. Results are reported in J/m (joules per meter of notch) for Izod and J/m2 for Charpy. The standard falls under ASTM Committee D20 on Plastics.
Applications
- Material selection and comparison for injection-molded plastic parts subject to impact loads
- Quality control of incoming plastic pellets and molded part production
- Effect of glass fiber reinforcement, rubber toughening, or impact modifier additives on impact resistance
- Temperature dependence of impact resistance -testing at sub-ambient temperatures to simulate cold service
- Weld line and knit line impact strength evaluation in injection molded parts
- Effect of moisture conditioning or environmental exposure on plastic impact behavior
- Packaging material selection for impact protection in distribution environments
- Comparative testing of competing plastic grades or resin systems for a given application
Benefits
- Fast, simple test that provides a direct measure of a material’s resistance to sudden impact loading
- Multiple methods in one standard cover notched, unnotched, and reversed notch configurations
- Notch sensitivity characterization available by testing at multiple notch radii
- Results in standard units allow direct comparison across materials, suppliers, and labs
- Widely required in plastic material data sheets and component specifications across all industries
- Sub-ambient temperature testing capability identifies brittle-to-ductile transition behavior in cold service materials
- Applicable to virtually all rigid and semi-rigid plastic materials
ASTM D256 Izod Impact Testing of Plastics Process
Specimen Preparation and Notching
Specimens are machined or injection-molded to the required dimensions.
1Pendulum Setup and Verification
The pendulum hammer energy capacity is selected to be appropriate for the material
2Impact Testing
The specimen is positioned in the fixture and the pendulum is released.
3Calculation and Reporting
Impact strength is calculated by dividing the absorbed energy by the specimen width (Izod, J/m) or by the specimen cross-sectional area at the notch
4ASTM D256 Izod Impact Testing of Plastics Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D256-23 |
| ASTM Committee | D20 – Plastics |
| Methods Covered | Method A (notched Izod), B (notched Charpy), C (unnotched Izod), D (reversed notch Izod), E (tensile impact) |
| Standard Notch Radius | 0.25 mm |
| Izod Specimen Size | 63.5 mm x 12.7 mm, varying thickness |
| Charpy Specimen Size | 127 mm x 12.7 mm, varying thickness |
Instrumentation Used for ASTM D256 Izod Impact Testing of Plastics
- Pendulum impact tester with appropriate energy capacity hammers for Izod and Charpy configurations
- Notching machine with 0.25 mm radius cutter for standard notch preparation
- Optical comparator or microscope for notch geometry verification
- Environmental conditioning chamber at 23 degrees C and 50% RH
- Temperature-controlled bath or chamber for sub-ambient and elevated temperature testing
- Digital or dial energy readout system on the pendulum tester
- Micrometer for specimen dimension measurement
ASTM D256 Izod Impact Testing of Plastics Results and Deliverables
- Notched Izod impact strength in J/m for each specimen and average for the lot
- Notched Charpy impact strength in J/m2 where Method B is applied
- Fracture type classification for each specimen -complete break, hinge break, partial break, or non-break
- Unnotched impact values where Method C or D is applied
- Conditioning temperature, humidity, and duration
- Specimen dimensions and notch geometry measurements
- Material identification and specimen preparation method (molded or machined)
- Full test report with all individual and average results formatted for material data sheet, design, or incoming inspection use
Frequently Asked Questions
The ASTM D256 Izod Impact Test measures the impact strength of materials, typically plastics, to determine their ability to resist sudden or forceful impacts.
The ISO 180 Izod Impact Test aims to determine a material's impact strength or toughness, typically plastics, by measuring its ability to resist a sudden, forceful impact.
The notch is critical because it creates a weakened point in the specimen.
Yes, ASTM D256 can be used for thermoplastics, thermosets, and elastomers.
Why Choose Infinita Lab for Advanced Materials Testing and Characterization?
At the core of this breadth is our network of 2,000+ accredited laboratories across the USA, offering access to over 10,000 testing methods and analytical services. From advanced materials characterization (SEM, TEM, RBS, XPS) to mechanical, chemical, environmental, biological, and standardized ASTM/ISO-compliant testing, we deliver unmatched flexibility, specialization, and scale. You are never limited by geography, facility, or methodology — Infinita Lab connects you to the right expertise and testing solution, every time.
Looking for a Trusted Partner for Accurate and Reliable Testing Services?
Send query us at hello@infinitlab.com or call us at (888) 878-3090 to learn more about our services and how we can support you.
Request a Quote
Submit your material details and receive testing procedures, pricing, and turnaround time within 24 hours.
Quick Turnaround and Hasslefree process
Confidentiality Guarantee
Free, No-obligation Consultation
100% Customer Satisfaction
