ASTM D256, ISO 180 Determination of Izod Pendulum Impact Resistance of Plastics

Get Certified ASTM D256 Testing for Plastic Impact Strength

ASTM D256 certification is a standardized measurement of Izod pendulum impact resistance of plastics. Compliance checks whether plastic materials can absorb abrupt impact forces without breaking. ASTM D256 is a toughness test used for material evaluation before being accepted for manufacturing and quality control. Evaluation and certification ensure compliance with the ASTM D256 requirements and reduce the risk of product failure from poor impact performance for plastic components.

The scope of ASTM D256 includes: 

• Material type: Plastics subjected to pendulum-type hammers. 
• Purpose: Determine the resistance of the material to impact by a pendulum under standardized conditions.
• Properties measured: Energy absorbed per unit of specimen width, or per cross-sectional area under the notch. 
• Method: Test Method A (Cantilever Beam Test) for general materials and Test Method C for materials with Izod impact resistance less than 27 J/m (0.5 ft·lbf/in.).
• Result: Impact resistance is reported as the amount of energy absorbed per unit width or per area under the notch. 
• Test Limitations: Fabrication method, notch method and rate, notch quality, time between notching and test, specimen size, and environmental conditioning all have a significant effect on the results. 
• Environmental conditions: Specimens are conditioned for a minimum of 40 hours at 23 ± 2°C and 50 ± 5%RH or other prescribed conditions as necessary.
• Applications: Material specification, quality control, research and development, and comparison of plastic toughness.

What are the Uses of ASTM D256 Testing?

ASTM D256 is used to assess the resistance of plastics to impact under controlled conditions. Engineers then use the outcome to evaluate material toughness and ensure the material is appropriate for the use. This standard:

• Determines the resistance of plastics to pendulum-type hammers.
• Gives Test Method A for general materials and Test Method C for low impact resistance materials.
• Assesses the effect of notch sensitivity on impact behaviour.
• Enables Quality Control and Material Specification for plastic products.
• Allows comparison of different formulations of plastics and batches.
• Helps to anticipate the performance of material under impact loadings.

What Materials Can Be Tested Under ASTM D256? 

ASTM D256 is used for plastics tested using pendulum-type hammers. The method involves specimens with a milled notch, and the notch generates a stress concentration, which makes brittle fracture more likely. Test Method C is for use with materials having an Izod impact resistance of less than 27 J/m (0.5 ft·lbf/in.). Before starting the evaluation program, the type of material and the proper test method must be confirmed, depending on the expected impact resistance. 

Why is ASTM D256 Important? 

ASTM D256 is significant as it specifies controlled procedures for the assessment of impact resistance in plastics. The notch on the Izod specimen focuses the stress, reduces plastic deformation, and guides the crack through the specimen behind the notch. The results help manufacturers to select materials and to decide on whether a plastic material will be acceptable for impact loading. The standard establishes a common test procedure for evaluating impact resistance, which is referenced in plastic specifications. 

ASTM D256 Testing Process and Data Collection

The Testing process starts when the analyst selects the test method depending on the impact resistance that is expected from the material. Technicians notch and set up notched specimens in the Izod impact tester. The operator then lets the pendulum go, striking the specimen. Technicians measure the amount of energy absorbed during breakage and record it to determine the impact resistance of the material. Lastly, specimen dimensions, notching parameters, and test conditions are documented. 

Common Challenges and Troubleshooting

To obtain accurate ASTM D256 results, there is a need to prepare the specimens correctly, ensure the notch is of the appropriate quality, and ensure consistent testing conditions are maintained. Poor specimen preparation, environmental conditions, machine calibration, sample handling and storage, and test setup inconsistencies are some of the challenges experienced during testing. Troubleshooting these problems would require proper specimen preparation, a consistent testing environment, proper calibration of the impact testing machines, and proper specimen handling. 

• Analysts report impact resistance as energy absorbed per unit of specimen width or per unit of cross-sectional area under the notch.
• Technicians record the test method used (A or C) and dimensions of specimens.
• Analysts record the notching parameters and time between notching and test.
• Engineers consider that the result is strongly influenced by the parameters of the specimen preparation and testing.
• Manufacturers utilize evaluation data to guide material selection and quality control decision-making. 

Link to ASTM D256