ASTM D638 Tensile Testing of PlasticTensile testing plastics is the process of stretching or pulling an object with a constantly changing force. ASTM D638 covers the tensile properties of both reinforced and unreinforced plastics in the form of dumbbell-shaped molded plastic test specimens.

If you plan on conducting ASTM D638 we recommend acquiring the test standard from ASTM directly. There are many important details regarding this test method that are provided which are key to achieving successful results. Every standard provides important environmental conditions, test sample preparation and conditioning requirements, sample dimensions and test reporting expectations. It’s critical that you fully understand the standard so that you can set up the test, run the procedure, and report the results requirements.

Why ASTM D638?

If you are testing rigid plastic samples between 1 to 14 mm (0.03 to 0.55 in) then ASTM D638 is right for you.

How Do I Perform ASTM D638?

ASTM D638 establishes procedures for collecting data using a universal testing machine (UTM). You must start by measuring the thickness of the sample. The most common specimen is Type I, which has a thickness of 3.2 mm (0.125 in) and a gauge length of 50 mm (2 in). That material thickness reflects common plastic components and allows for good strain measurement accuracy.

Using the universal test machine, the specimen is placed between two clamps or grips with the edges of the specimen parallel to the direction of the load. The specimen grips are tightened to hold the specimen securely within the fixture. The test specimen is then pulled apart at tensile rates ranging from speeds from 1 to 500 mm/min (0.3 to 19.6 in/min) until it breaks.

ASTM D638 Test Machines & Accessories

How Do I Choose the Best Plastic Sample Type For ASTM D638?

  • Flat specimens are typically molded, die-cut, or machined into a dogbone or dumbbell shape, which ensures that the break occurs in the center of the specimen rather than at the clamping areas.
  • Type I specimens have a gauge length of 50 mm (2 in). If a Type I sample break cannot be produced in the narrow parallel portion of the dumbbell specimen, ASTM D638 recommends use of a Type II specimen, where the width of the narrow parallel section is reduced.
    Rigid tubes and rods, both of which must also be machined into a dogbone shape.
  • If specimens are more than 7 mm (0.27 in) thick, then a Type III is used. Multiple dimensions ensure that the specimen thickness remains less than the width. If sheet thickness is more than 14 mm (0.55 in), thickness is adjusted through machining or reducing the sample down to 14 mm (0.55 in) or less.
  • If only a small amount of material is available, then a specimen Type V is used, which is reduced in every dimension versus a Type I. Type V specimens are smallest, with a gauge length of only 7.6 mm (0.3 in).

What Values Do You Need to Report to Conform With ASTM D638?

These are the most common tensile properties calculated using ASTM D638 and can be collected using our controller software:

  • Tensile strength
  • Tensile modulus
  • Elongation
  • Poisson’s Ratio

Articles Related to ASTM D638 Testing

ASTM D638 Tensile Testing Machines

5 or 10 kN (1,125 or 2,250 lbf) test machines are the most common sized universal or tensile testing machine for molded plastics. A higher capacity 50 kN (11,250 lbf) unit may be required as reinforced plastics and composites increase in strength.

240 Family Electromechanical Universal Test Machine

Best Performance & Value - 5 kN (1,125 lbf)

The 240 Family is the ideal solution for a wide range of tests and features higher travel and faster speeds compared to traditional universal test machines. The load frame is compact and lightweight which is great if space is limited. Complete system includes controller software, load frame and grips specifically configured for your test requirements.

Learn more about this test machine          Request a quote

311 family Electromechanical Universal Test Machine

Most Versatile - 10 kN (2,250 lbf)

The 311 series tabletop machines are configured to your exact needs including performance, flexibility, simplicity and affordability. This frame is best for smaller loads and a higher speed. Complete system includes controller software, load frame and grips specifically configured for your test requirements.

Learn more about this test machine          Request a quote

313 Family Electromechanical Universal Test Machine

Most Versatile - 50 kN (11,250 lbf)

The 313 family tabletop machines are configured to your exact needs including performance, flexibility, simplicity and affordability. This frame is best when you need a higher capacity system for reinforced plastics and composites. Complete system includes controller software, load frame and grips specifically configured for your test requirements.

Learn more about this test machine          Request a quote

ASTM D638 Accessories

ASTM D638 Tensile Grips

Vise style pneumatic grips with serrated jaws are a good choice for a variety of reasons. First, it’s important that the specimen is held securely. Since plastic samples contract laterally (Poisson's ratio effect) as the sample is pulled in tension, pneumatic vise grips recommended. Pneumatic vice grips self-adjust to maintain clamp load during the test. Sample misalignment can be minimized with a simple alignment tool that mounts directly onto the grip jaw, providing an adjustable stopping point so operators can easily tell that their specimen has been aligned correctly. Wedge action grips are also known as ‘self aligning’ grips and commonly used as sample sizes and loads increase. Loads can increase in the case of testing reinforced plastics.

G83 Pneumatic Side Opening Grips

Rated up to 3.5 kN (750 lbf)

Learn more          Request a quote

G622 Mechanical Wedge Grip

Rated up to 10 kN (2,250 lbf)

Learn more          Request a quote

G175 Pneumatic Wedge Grips

Rated up to 50 kN (11,250 lbf) and -70 to +280 C (-94 to +536 F)

Learn more          Request a quote

ASTM D638 Extensometers

ASTM D638 material testing calculations require strain values to establish accurate modulus of elasticity. Extensometers measure the strain in response to tensile force. Both clip on units and non contacting video extensometers are available depending on preference. Note that extensometers are needed for high accuracy modulus measurements, and not needed for elongation at break measurements because the machine's crosshead position is valid for that value.

ASTM D638 Video Extensometer

VE-D638 Video Extensometer

         Request a quote

ASTM D638 Cutting Dies

DD638 Cutting Dies (Type I, II, III, IV & V)

I, II, III, IV, or V cutting dies matched to ASTM D638 specimen types.

Learn more          Request a quote

 

Note: This is not a complete summary of the standard. Anyone planning to conduct this test should read the full standard.