ASTM D790
Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics
Summary Description
The ASTM D790 test standard specifies the characterization of flexural properties of unreinforced and reinforced plastics. The test is performed by applying a flexural load to a standard specimen. Common properties that reference ASTM D790 include the flexural modulus, flexural strength and strain at yield, flexural stress and strain at peak load (more appropriate for ductile plastics) and at break (more appropriate for brittle plastics), flexural stress-strain curve, and offset yield stress and strain at flex.
Additional Test Standards of Relevance
- ISO 178
- ASTM D6272
Characterization Measurements and Relevant Tests
DatapointLabs offers a number of tests that address different properties covered under the ASTM D790 standard. These include the following characterization measurements [bracketed links refer to relevant tests in the DatapointLabs Test Catalog]:
Flexural Modulus and Flexural Strength
- Flexural modulus, flexural strength at yield under 3-point or 4-point test [M-015]
Flexural Stress-Strain
- 3-point flexural stress-strain curve, flexural strength at peak load, flexural strain at peak load, offset yield strain at flex, offset yield stress at flex, and flexural modulus [M-221]
- 4-point flexural stress-strain curve, flexural strength at break, flexural strain at break, offset yield strain at flex, offset yield stress at flex, and flexural modulus [M-225]
High-Speed Flexural Stress-Strain
- 3-point flexural stress-strain curve, flexural strength at peak load, flexural strain at peak load, offset yield strain at flex, offset yield stress at flex, and flexural modulus at crosshead speeds up to 1m/s [M-230]
Test Procedure and Equipment Used
The specific test procedure will vary by test and the individual test webpages (linked to above and below) should be consulted for relevant descriptions. In general, a universal testing machine (UTM) is used to determine the appropriate flexural property or properties under measure. The test specimen is placed on a span. The UTM crosshead, with either a single-point nose (3-point test) or double-point nose (4-point test), is lowered until just above specimen. The test is performed at a constant velocity, using a calculated value for the required strain rate. The load and corresponding specimen deflection are recorded. The double-point nose of a 4-point test provides a distribution of applied stress and is used in cases where the single-point nose of a 3-point test would create a region of localized stress concentration. For high-speed flexural characterization, a Dynatup 8250 drop tower is used instead of a UTM.
Sample Conditioning and Non-Ambient Testing
Sample conditioning, if required, is carried out following specimen preparation in accordance with ASTM D618. Typical conditioning selections are ‘dry as molded’ (low humidity storage at 23°C) and 40 hours at 23°C and 50% relative humidity. Non-ambient testing may be carried out at any temperature between -53°C and 200°C.
Test Specimen Specification and Description
Specimen specifications under ASTM D790 are as follows:
- Flex bar specimens specified by ASTM D790 or ISO 178
- Alternatively, specimens can also be prepared from the gage section of ASTM D638 Type I or ISO 527 Type 1A tensile bars, or may be machined from flat sheet or plaques
- See Flex Bars for further details
Characterization Measurement Descriptions
Typical characterization measurements under ASTM D790 include:
- Flexural Modulus: The ratio of flexural stress (load) to the corresponding strain (flexural deformation), measured below the elastic limit of a material
- Flexural Strength at Yield: The maximum flexural stress at the point where a material transitions from elastic to plastic behavior (Yield Point)
- Flexural Strain at Yield: The measurement of beam deflection at the point where a material transitions from elastic to plastic behavior (Yield Point)
- Flexural Strength at Peak Load: The maximum flexural stress applied under flexural loading
- Flexural Strain at Peak Load: The measurement of beam deflection at the point of maximum flexural load
- Flexural Strength at Break: The maximum flexural stress applied at the point of material break under flexural load
- Flexural Strain at Break: The measurement of beam deflection at the point of material break under flexural load
- Flexural Stress-Strain Curve: The graphical relationship between flexural stress and the measurement of beam deflection in a material under flexural load
- Offset Yield Stress in Flex: The offset yield method determines the yield point by the intercept of the stress-strain curve and a line with slope corresponding to the elastic modulus and a strain offset (nominally 0.2%); the offset yield stress is the stress at the determined intercept
- Offset Yield Strain in Flex: The offset yield method determines the yield point by the intercept of the stress-strain curve and a line with slope corresponding to the elastic modulus and a strain offset (nominally 0.2%); the offset yield strain is the strain at the determined intercept
Complete Listing of DatapointLabs Tests Referencing ASTM D790
The entire list of tests in the DatapointLabs test catalog that reference ASTM D790 are as follows:
