ASTM D790 is the global industry standard for determining the flexural properties of unreinforced and reinforced plastics, as well as electrical insulating materials. This test is critical for evaluating how a material resists bending forces and establishes the material’s stiffness and strength in a three-point loading configuration.
The Mechanics of Flexural Testing
Unlike a tensile test which pulls a specimen apart, an ASTM D790 test applies a downward force at the center of a rectangular bar supported at two points. This creates a combination of tensile stress on the bottom of the specimen and compressive stress on the top.
Key data points derived from this test include: Flexural Strength: The maximum stress a material can withstand during a bending test before it breaks or deforms permanently. Flexural Modulus: A measure of the material’s stiffness, determined by the ratio of stress to strain in the initial elastic region of the test. Flexural Strain: The amount the material has deformed at the outer surface of the specimen.
TRI System Configuration
To achieve consistent results that comply with ASTM D790, the testing hardware must maintain a precise strain rate. TRI systems utilize the Newton Controller to manage constant-rate-of-extension (CRE) protocols. The 100 and 200 Series frames are the standard choice for plastic flexural testing, featuring modular three-point bend fixtures that ensure perfect axial alignment. For high-accuracy modulus calculation, TRI recommends using a secondary strain channel to measure mid-span deflection directly.