ASTM D638
Standard Test Method for Tensile Properties of Plastics
Micom offers testing services according to ASTM D638, which measures the tensile properties of unreinforced and reinforced plastics, including ultimate tensile strength, yield strength, and elongation. Testing the properties of plastics through physical and mechanical testing is an essential aspect of product development and quality control.
ASTM D638 is the most common method run in our tensile testing lab for plastics, alongside ASTM D412 for rubber and elastomers and ASTM D882 for thin films.
ASTM D638 Testing Method
In ASTM D638 Testing, the samples are cut in the form of a standard dumbbell shape. This cut ensures the sample has a reduced section where the break will occur upon testing. A universal tester is used to grip and pull the specimen until failure. The samples are tested in specific conditions such as pre-treatment, sample orientation, temperature, humidity, and testing machine speed.
The ASTM D638 testing standard can be used for testing materials up to 14 mm (0.55 in.) in thickness. However, thin sheeting materials, including film less than 1.0 mm (0.04 in.) in thickness, should be tested using the ASTM D882 test.
Micom Laboratories is A2LA accredited to perform ASTM D638 testing as part of our plastic testing services. Our testing experts ensure the accuracy and reproducibility of the results by carefully modulating the dimensions of the dumbbell, optimizing the cutting process, and controlling the testing conditions.
Contact us to get more information about our plastics and polymer testing services.
Key Mechanical Properties Measured by ASTM D638
The ASTM D638 standard test method for evaluating the tensile properties of plastics involves determining crucial mechanical properties of moulded plastics or specimens obtained from a specific region of a plastic component. The most essential mechanical properties measured are:
- Ultimate tensile strength (UTS): This is the maximum stress that the specimen can withstand before it breaks.
- Yield strength: This is the stress at which the material starts to deform plastically, meaning it does not return to its original shape after the stress is removed.
- Elongation at break: This is the percentage of deformation that occurs in the specimen at the point of failure.
- Modulus of elasticity: This is a measure of the stiffness of the material.
These properties are critical outcomes of physical and mechanical testing of polymers and provide valuable data for material selection and product validation.
ASTM D638 Typical Experimental Parameters
When testing the tensile properties of plastics, the following key parameters must be considered to ensure accurate and reproducible results.
Number of specimens per product: Five specimens are typically tested to ensure accuracy and reproducibility. In some cases, the tensile properties need to be measured both in the machine and perpendicular to the machine’s direction as they can vary substantially from one orientation to the other. This behaviour is called anisotropy.
Crosshead speed: The crosshead speed varies as a function of the material’s rigidity, shape, and thickness. Typically, the softer the material, the faster it will get pulled. The crosshead speed should be between 5 mm per min and 500 mm per min. Please refer to table 1 of the test methods for specific details or contact our experts for assistance.
Dumbbell type: The dumbbell dimensions are modulated as a function of the material’s thickness. Sample cutting is of paramount importance for obtaining accurate and reproducible test results. Dumbbe