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ASTM D 256

Understanding ASTM D256: The Impact Resistance of Plastics


In the rapidly evolving world of materials science, the need for durable and reliable plastics has never been more critical. From automotive components to consumer electronics, the impact resistance of plastics plays a pivotal role in the longevity and functionality of a wide range of products. ASTM D256 is a standardized testing methodology that provides a measure of the impact resistance of plastic materials. This blog post delves into the significance of ASTM D256, the standardized testing methods involved, specimen preparation and dimensions, components of the test report, and the broader implications of testing data in the field of materials science.


Significance: The significance of ASTM D256 cannot be overstated. It offers a quantifiable measure of a material’s toughness—its ability to absorb energy and withstand sudden impacts without fracturing. This standard is crucial for materials engineers and designers in selecting the right plastic materials for specific applications, ensuring that products meet the necessary safety, quality, and performance standards.

Standardized Testing Methods: ASTM D256 outlines several methods for determining the impact resistance of plastics, including the Izod and Charpy impact tests. These methods involve striking a notched specimen of the material with a pendulum hammer and then measuring the energy absorbed by the specimen during fracture. The choice between Izod and Charpy tests depends on the material properties and the specific application requirements.

Specimen Preparation and Dimensions: Specimen preparation is a meticulous process that directly affects the accuracy and reliability of the test results. According to ASTM D256, specimens are typically machined into a standardized shape with a precise notch to focus the impact at a specific location. The dimensions of the specimen are critical; they must adhere to the specifications outlined in the standard to ensure consistency across tests. For example, specimens for the Izod impact test are usually 63.5 mm long, 12.7 mm wide, and have a thickness ranging from 3.2 mm to 12.7 mm, depending on the material’s characteristics and the test requirements.

Test Report Components: A comprehensive test report is a critical component of ASTM D256, detailing the methodology, conditions, and results of the impact resistance test. The report should include a description of the specimen material, preparation procedures, test conditions (such as temperature and humidity), the type of impact test performed (Izod or Charpy), and the test results. This report is invaluable for interpreting the material’s behavior under impact and for comparing the impact resistance of different materials.

Implications of Testing Data: The data obtained from ASTM D256 testing have far-reaching implications in materials science and engineering. By understanding the impact resistance of plastics, engineers can design more durable and reliable products, reduce material failure rates, and enhance consumer safety. Additionally, this data supports the development of new materials and the improvement of existing ones, driving innovation in the plastics industry.

Other Considerations: While ASTM D256 provides a robust framework for assessing impact resistance, it’s essential to consider other material properties, such as tensile strength, flexibility, and thermal resistance, in comprehensive material selection processes. Material testing is a multifaceted discipline that requires a holistic approach to ensure the optimal performance of plastics in their final applications.

Izod impact


ASTM D256 is a cornerstone of materials testing, offering critical insights into the impact resistance of plastics. Through standardized testing methods, meticulous specimen preparation, and detailed reporting, this standard helps engineers and designers select the most appropriate materials for their needs. As we continue to push the boundaries of material science, the insights gained from ASTM D256 will play a crucial role in shaping the future of plastic materials and their applications in various industries.