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ASTM D 638

Unveiling the Strength of Plastics: A Deep Dive into ASTM D 638


ASTM D 638, titled "Standard Test Method for Tensile Properties of Plastics," is a methodology developed by ASTM International. It is designed to determine the tensile strength, elongation, yield point, and modulus of elasticity of plastic materials. These parameters are crucial for engineers and designers to select the appropriate plastic materials for specific applications, ensuring durability, functionality, and safety.

ASTM D 638

Why ASTM D 638 Matters

The tensile properties of plastics can significantly affect their performance and longevity. Understanding these properties helps in:

  • Material Selection: Ensuring the plastic material can withstand the forces it will encounter during use.
  • Quality Control: Manufacturers can ensure their products meet the required specifications and performance standards.
  • Research and Development: Facilitates the development of new materials with improved properties.

Specimen Dimensions: The Heart of Precision

One of the critical aspects of ASTM D 638 is the specification of specimen dimensions. The standard outlines multiple specimen types to accommodate various material thicknesses and properties. The most commonly used specimen for testing is the Type I specimen, which has the following dimensions:

  • Overall Length: 165 mm
  • Width in Narrow Section: 13 mm
  • Thickness: Varies, typically ranging from 3.2 mm to 14 mm, depending on the material being tested.

These dimensions are meticulously defined to ensure that the test results are accurate and reproducible. The shape and dimensions of the specimen play a crucial role in the uniform application of tensile forces and the accurate measurement of the material’s properties.

Conducting the Test

The testing process involves clamping the specimen in a tensile test machine and applying a force until the specimen fails. The machine records the force applied and the elongation of the specimen. From these data, various tensile properties are calculated and analyzed.

Implications of Testing Data

The data obtained from ASTM D 638 testing are invaluable for various stakeholders:

  • Designers can tailor their designs based on the material properties to enhance product performance.
  • Manufacturers ensure that their material meets the required specifications for their application.
  • Consumers benefit from products that are reliable and fit for purpose, backed by rigorous testing.
Plastic Testing


ASTM D 638 plays a pivotal role in the plastics industry, providing a standardized method to evaluate tensile properties. The precise specification of specimen dimensions ensures the reliability and comparability of test results, making it an indispensable tool for material selection, quality control, and innovation in plastic materials.


  1. Can ASTM D 638 be used for all types of plastics?

    • Yes, ASTM D 638 is applicable to a wide range of plastic materials, including thermoplastics and thermosetting plastics.
  2. How do the tensile properties influence the application of plastics?

    • Tensile properties determine how a material will react under tensile forces, influencing its suitability for various applications, including load-bearing components, flexible materials, and more.
  3. Are there any limitations to the ASTM D 638 test?

    • While ASTM D 638 provides comprehensive insights into the tensile properties of plastics, it is one of many tests available. Depending on the application, other properties such as impact resistance, compressive strength, or thermal properties may also need to be considered.