Tensile Strength Test on Plastics According to ASTM D638

Plastic tensile testing according to ASTM D638 is a common standard for determining physical and mechanical properties of materials. ASTM D638 is prepared by applying traction to the sample and measuring the different properties of the test piece under stress. Although ASTM D638 measures many different tensile properties, the most common is:

  • Tensile strength – the amount of force that can be applied to a plastic before it yields (stretches irreparably) or breaks.
  • Tensile modulus – how much a material can deform (stretch) in response to stress before it yields. Modulus is a measurement of the material’s stiffness.
  • Elongation – the increase in gauge length after break divided by the original gauge length. Greater elongation indicates higher ductility.
  • Poisson’s Ratio – a measurement of the relationship between how far a material is stretched and how thin it gets during the stretching process.

There are many different testing methods for plastic materials. ASTM D638 applies only to plastic samples with a thickness of 1 mm to 14 mm. If the test piece is one piece of thickness less than 1mm, use another standard, ASTM D882. If you experiment with elastic materials, use ASTM D412. These methods can be found in application modules of Bluehill Universal – the software is compatible with most ISO and ASTM standards.



There are 5 test samples allowed in ASTM D638 test, the difference between these samples is dependent on the thickness of the sample and available materials. The most commonly used sample is the I-type, 3.2mm thick. This sample is about 165 mm long and 13 mm wide, measuring 50 mm in standard length. Extruded flat specimens. In addition, flattened specimens also allow testing of I-shaped steel pipes and rods.

In case of limited materials, many labs will use it Use a V-shaped or IV pattern. The required size for sample IV is the same as that required for ASTM D412 meaning stain The same cut can be used. The V-type is the smallest with the measured length The standard is only 0.3 in.

All test samples must be measured before testing ASTM D5947 standard. Most typical micromatch should be suitable to implement this measurement.

Die-cut or machined samples need to be measured individually, but operators using injection molded specimens only need to measure a single sample from a sample lot providing the variation in that sample lot is proven to be less than 1%. Injection molded specimens are often produced with a draft angle instead of being perfectly square, which must be taken into consideration when measuring the specimen. Always make sure that width measurements are taken at the center of the draft angle.

Features Automatic sample measuring device in Bluehill Universal allows operators to connect up to two microchips or measuring devices to a computer and enter data directly into the software. This eliminates input errors and increases efficiency.  



Most ASTM D638 tests are performed on top table universal testing machines. A 5 kN or 10 kN (1125 or 2250 lbf) system is the most common, but because of the machined plastics and composite materials with high rigidity the system may be required to be 30kN or 50 kN.



The most important thing is to keep the test piece firmly in the tractor. The most suitable clamp is the pneumatic clamp. With pneumatic clamps, clamping force is maintained by air pressure, unchanged even when the test piece thickness changes significantly during testing. For forces above 10 kN, usually found only with reinforcing materials, manual wedge action clamps should be used.



When presenting test results, it is important to make sure ensure that the terms are correctly defined to ensure compliance with standards and creation Conditions comparing data between different laboratories.

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