ASTM D638 Standard Test Method for Tensile Properties of Plastics
The test methods in this standard are used to produce control data of tensile properties in plastic materials. The use of this particular test method is provisional based on the material specifications which may allow for some procedural modifications that must take precedence when adhering to the material specification.
Tensile tests measure the force required to break a plastic sample specimen and the extent to which the specimen stretches or elongates to that breaking point.
ASTM D-638 tensile test procedure:
Specimens are placed in the grips of the universal tester at a specified grip separation and pulled until failure. For ASTM D 638 the test speed is determined by the material specification. An extensometer is used to determine elongation and tensile modulus.
Specimen size: The most common specimen for ASTM D-638 is a Type I tensile bar.
The following calculations can be made from tensile test results:
Tensile strength (at yield and at break)
Elongation and percent elongation at yield
Elongation and percent elongation at break
This test method covers the determination of the tensile properties of unreinforced and reinforced plastics in the form of standard dumbbell-shaped test specimens when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed.
This test method is applicable for testing materials of any thickness up to 14 mm (0.55 in.). However, for testing specimens in the form of thin sheeting, including film less than 1.0 mm (0.04 in.) in thickness, ASTM standard is the preferred test method. Materials with a thickness greater than 14 mm (0.55 in.) shall be reduced by machining.
This test method includes the option of determining Poisson’s ratio at room temperature.
NOTE 1: This standard and ISO 527-1 address the same subject matter, but differ in technical content.
NOTE 2: This test method is not intended to cover precise physical procedures. It is recognized that the constant rate of crosshead movement type of test leaves much to be desired from a theoretical standpoint, that wide differences may exist between rate of crosshead movement and rate of strain between gage marks on the specimen, and that the testing speeds specified disguise important effects characteristic of materials in the plastic state.
Further, it is realized that variations in the thicknesses of test specimens, which are permitted by these procedures, produce variations in the surface-volume ratios of such specimens, and that these variations may influence the test results. Hence, where directly comparable results are desired, all samples should be of equal thickness. Special additional tests should be used where more precise physical data are needed.
NOTE 3: This test method may be used for testing phenolic molded resin or laminated materials. However, where these materials are used as electrical insulation, such materials should be tested in accordance with Test Methods and Test Method .