ASTM D638 Plastics Tensile Testing

ASTM D638  Test Scope

Plastic Tensile Testing by ASTM D638 calculates different tensile properties such as tensile strength, breaking strength, and maximum elongation of reinforced and unreinforced plastics. The standard test samples are made in the form of dumbbell-shaped. The samples are tested under defined pretreatment conditions, temperature, humidity, and testing machine speed. ASTM D638 test is used to measure the force required to rupture a plastic sample and determine the extent to which the sample elongates to the breaking point.

The tensile test specimen (ASTM D638 Type 1, t = 3.2 mm). 

ASTM D638 Test Procedure

For the ASTM D638 test, samples are mounted in the universal tester. Samples are placed in the tester in such a way that the grips of the tester are at a specified grip separation and pulled until failure. The test speed of the material is determined as defined by ASTM D638. The extensometer determines the elongation and tensile modulus.

This ASTM D638 test method aims to generate tensile property data for the specification and control of plastic materials. Additionally helpful for qualitative characterization, these data are also beneficial for research and development.

Some material specifications require this test technique, but some procedural changes take precedence when conforming to the specification. So, before applying this test method, it is advised to consult that material specification.

Elevated or reduced temperature test procedure:

The Universal Test machine is equipped with a thermal chamber. This chamber allows traveling across the top and bottom of the chamber on the foundation and the crosshead of the Universal Tester. Standard measurement devices are mounted inside the chamber, and the thermally monitored atmosphere is tested in the same way as at ambient temperature. The chamber has internal electric heaters to maintain high temperatures, and external carbon dioxide is used as the coolant to lower temperatures. The size of the chamber limits the ultimate elongation that is possible. The extensometers here are usually limited to 200 °C or more.

ASTM D638 Test Sample Size

The most common sample for ASTM D638 is a Type I tensile bar. This test procedure can evaluate materials with thicknesses up to 14 mm (0.55 inches). However, ASTM D882 is the ideal test technique for testing specimens that are in the form of thin sheeting. This includes film less than 1.0 mm (0.04 inches) in thickness. Materials that are thicker than 14 mm (0.55 inches) must be machined down.

ASTM D638 Test Conclusion

ASTM D638 is the most common testing standard for determining the tensile properties of reinforced and non-reinforced plastics.