ASTM D 790

ASTM D 790 - Flexural Properties of Materials


When it comes to assessing the mechanical properties of plastics, the ASTM D 790 standard emerges as a pivotal benchmark within the materials testing domain. This standard outlines the procedures for determining the flexural properties of unreinforced and reinforced plastics, including high-modulus composites and electrical insulating materials. Such evaluations are crucial for industries where the flexural strength and stiffness of materials dictate the quality and durability of the final products.

Exploring Bendability: How Plastic Handles the Flexural Test

The Significance of Flexural Testing

Flexural testing, or bend testing, provides insights into a material’s ability to withstand bending forces. This form of testing is essential for materials destined for applications where resistance to bending or deformation under load is critical. By employing ASTM D 790, manufacturers and researchers can predict how materials will behave in real-world applications, ensuring that products meet the necessary safety, reliability, and performance standards.

Standardized Testing Methods: ASTM D 790 Overview

ASTM D 790 specifies two primary methods for conducting flexural tests:

  • Method A (Three-Point Bending Test): Involves supporting the material specimen at two points and applying force at a third point, located midway between the supports.
  • Method B (Four-Point Bending Test): Consists of supporting the specimen at two points with two additional points where the force is applied, distributing the bending moment more uniformly across the central section of the specimen.

These methods allow for the determination of flexural properties, including the flexural strength (maximum stress experienced within the material at the moment of fracture) and flexural modulus (ratio of stress to strain in the elastic deformation phase).

Specimen Preparation and Dimensions

Critical to the integrity of ASTM D 790 testing is the precise preparation and dimensioning of specimens. The standard specifies the dimensions for test specimens, typically in the form of rectangular bars. The dimensions and preparation process ensure uniformity across tests, allowing for the reliable comparison of results. For definitive dimensions and preparation techniques, referring directly to the ASTM D 790 standard is recommended, as it provides detailed guidance to accommodate various materials and testing requirements.

Test Report Components

A comprehensive test report under ASTM D 790 includes:

  • Reference to the ASTM D 790 standard.
  • Detailed identification of the material tested, including its type, source, and any pretreatment.
  • The dimensions and shape of the test specimens.
  • Test conditions and any deviations from the standard method.
  • Results obtained, including flexural strength, modulus, and any observed material behavior during the test.

Implications of Testing Data

Data derived from ASTM D 790 testing plays a crucial role in material selection, quality control, and design process for numerous applications. Understanding a material’s flexural properties aids in predicting its performance under stress and helps in identifying suitable materials for specific applications, leading to safer and more efficient designs.

Other Considerations

While ASTM D 790 provides a comprehensive framework for flexural testing, it is vital for practitioners to consider factors such as material anisotropy, temperature, and environmental conditions, which may affect test results. Integrating these considerations ensures a more accurate and holistic assessment of material properties.

ASTM D 790


ASTM D 790 offers a standardized approach to measuring the flexural properties of plastics, playing a crucial role in material science and engineering. By meticulously adhering to the specified methods and considering all relevant factors, industries can continue to innovate and produce materials and products that meet the highest standards of quality and performance.


  1. What is flexural strength? Flexural strength is the maximum stress a material can withstand under bending before failure.

  2. How does temperature affect flexural testing? Temperature can significantly impact the mechanical properties of plastics, altering flexural strength and modulus.

  3. Can ASTM D 790 be used for composites? Yes, ASTM D 790 is applicable to both unreinforced and reinforced plastics, including composites.