ASTM D638 Tensile Properties of Plastics

Scope:

The ASTM D638 test technique generates tensile property data for controlling and specifying plastic materials. These data are beneficial for qualitative analysis and research and development.

Procedure:

In ASTM D638, each specimen’s width and thickness are measured to the nearest 0.025 mm (0.001 in. ), with flat specimens’ width and thickness measured in the center of either specimen and within 5 mm of each end of the gauge length. The interior and outside diameters of rod specimens, as well as the inside and outside diameters of tube specimens, are then measured to the closest 0.025 mm (0.001 in.) at a minimum of two sites 90° apart; these measurements are taken along the groove for specimens created in this manner. Plugs are employed in testing tube specimens. The specimen is put in the testing machine’s grips, with care taken to align the specimen’s long axis with an imaginary line connecting the grips’ points of attachment to the machine, and an extension indicator is attached. The load and extension curves at the yield point (if one exists) and at the moment of rupture are also recorded.

Specimen detail:

The specimen size should be according to the requirements. In this case, the ASTM D638 test technique is used to test materials with a thickness of up to 14 mm (0.55 in.). Materials with a thickness larger than 14 mm (0.55 in.) must be reduced by machining for testing specimens in thin sheeting, including film less than 1.0 mm (0.04 in.).

Result:

True strain is defined by the following equation for εr:

where:

dL = increment of elongation when the distance between the gage marks is L,

Lo = original distance between gauge marks, and

L = distance between gauge marks at any time.

Conclusion:

The ASTM D638 test technique involves determining the tensile characteristics of unreinforced and reinforced polymers using standard dumbbell-shaped test specimens under specified pretreatment, temperature, humidity, and testing machine speed conditions.