ASTM D638 Plastics Tensile Testing

ASTM D638 Plastics Tensile Testing

Scope:

Plastic Tensile Testing by ASTM D638 is done to calculate different tensile properties such as tensile strength, breaking strength, 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 conditions of pretreatment, temperature, humidity, and testing machine speed. ASTM D638 test is used for measuring the force that is required to rupture a plastic sample and also helps to determine the extent to which the sample elongates to that of the breaking point.

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

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 grips of the tester are at a specified grip separation and pulled until failure. The test speed of the material is determined as specified by ASTM D638. The elongation and tensile modulus are determined by the extensometer.

The purpose of this ASTM D638 test method is 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.

This test technique is required by some material specifications, but there are some procedural changes that 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 travelling across the top and bottom of the chamber on the foundation and the crosshead of the Universal Tester. Inside the chamber, standard measurement devices are mounted and the thermal monitored atmosphere is tested in the same way as it is 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 ultimate elongation that is possible is limited by the size of the chamber. The extensometers here are usually limited to 200 °C or more.

Video 01:  ASTM D638 & ISO 527 Tensile Testing of Plastic

Sample size: 

The most common sample for ASTM D638 is a Type I tensile bar. This test procedure can be used to evaluate materials with thickness 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.

Data:

Tensile strength (at yield and at break)

Elongation and percent elongation at yield

Elongation and percent elongation at break

Tensile modulus

Strain

Conclusion:

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