ASTM D638
Standard Test Method for Tensile Properties of Plastics
Summary Description
The ASTM D638 test standard specifies the characterization of tensile properties of unreinforced and reinforced plastics. The test is performed by applying a tensile load to a standard specimen. Common properties that reference ASTM D638 include the elastic and shear modulus, Poisson’s ratio, tensile strength, tensile stress-strain curve, offset yield stress and strain in tension, cyclic stress softening, and cyclic damage.
Additional Test Standards of Relevance
- ISO 527-1
- ISO 14129
- ASTM E8
- ASTM D412
Characterization Measurements and Relevant Tests
DatapointLabs offers a number of tests that address different properties covered under the ASTM D638 standard. These include the following characterization measurements [bracketed links refer to relevant tests in the DatapointLabs Test Catalog]:
Elastic and Shear Modulus
- Tensile modulus of elasticity (Young’s modulus) for both isotropic [M-011] and anisotropic [M-010] plastics
- In-plane shear modulus [M-013], including modulus in flow and cross flow directions, for orthotropic plastics
Poisson’s Ratio
- Poisson’s ratio and tensile modulus for isotropic plastics [M-101] or anisotropic plastics in the 1-2 direction [M-101] and the 2-3 direction [M-102]
Tensile Strength
- Tensile strength and tensile strain at yield or break, for ductile or brittle plastics, respectively [M-030] [M-130]
- Tensile modulus of elasticity, as well as tensile strength and tensile strain at yield or break [M-016]
Tensile Stress-Strain
- Tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, and tensile modulus [M-204]
- Tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, tensile modulus, and Poisson’s ratio [M-206]
- 2D DIC (digital image correlation) measurement of the tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, and tensile modulus for determination of strain at the localized yield point [M-204V2D]
- 3D DIC measurement of the tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, and tensile modulus for direct determination of true stress-strain [M-204V3D]
High-Speed and Very High-Speed Tensile Stress-Strain
- Tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, and tensile modulus at crosshead speeds up to 1m/s and strain rates up to 100/s [M-232]
- Tensile stress-strain curve, tensile strength at yield or break, offset yield stress and strain in tension, and tensile modulus at crosshead speeds between 1m/s-20m/s and strain rates between 100/s-2000/s [M-235]
Cyclic Stress Softening and Cyclic Damage
- Cyclic tensile stress-strain curve for characterization of cyclic Mullins effect (cyclic stress softening) in rubbers and elastomers [M-621]
- Tensile post-yield stress-strain curves under both loading and unloading conditions to determine damage beyond plastic strain [M-623]
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 tensile property or properties under measure. The test specimen is loaded between the grips of the UTM. A mechanical (contact) or video (non-contact) extensometer is used to measure strain. 2D and 3D digital image correlation (DIC) and high-speed video may also be used for extensometry, as appropriate. The tensile specimen is stretched at a constant speed while load and strain are recorded. The speed of testing – as defined by crosshead speed or strain rate – is specified by the standard or by client request. High-speed and very high-speed testing is also available.
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 D638 are as follows:
- Tensile bars relevant to ASTM D638 are ASTM D638 Type I, Type II, Type III, Type IV and Type V: see Specimens for further details
- Tensile bars may also be cut from suitable 4”x12” plaques: see Plaques for further details
- Tensile bar specimens may be dogbone (dumbbell) or straight-sided in configuration and may be either molded or cut, as appropriate to the specific test
Characterization Measurement Descriptions
Typical characterization measurements under ASTM D638 include:
- Tensile Modulus (Elastic Modulus or Young’s Modulus): The ratio of tensile stress (load) to the corresponding strain (elongation), measured below the elastic limit of a material
- Poisson’s Ratio: The negative ratio of transverse strain to axial strain under uniform axial stress, measured below the elastic limit of a material
- Tensile Strength at Yield: The maximum tensile stress at the point where a material transitions from elastic to plastic behavior (Yield Point)
- Tensile Strain at Yield: The maximum strain at the point where a material transitions from elastic to plastic behavior (Yield Point)
- Tensile Ultimate Strength: The maximum tensile stress at the point of material break
- Tensile Ultimate Strain: The maximum strain at the point of material break
- Engineering Tensile Stress-Strain Curve: The graphical relationship between stress and strain in a material under tensile load, based on the original cross-section of the test specimen
- True Tensile Stress-Strain Curve: The graphical relationship between stress and strain in a material under tensile load, based on the instantaneous cross-section of the test specimen
- Offset Yield Stress in Tension: 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 Tension: 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 D638
The entire list of tests in the DatapointLabs test catalog that reference ASTM D638 are as follows:
