ASTM E8 Tensile Testing of Metallic Materials using Automatic Extensometry

ASTM E8 describes tensile testing methods to determine yield strength, yield point elongation, tensile strength, elongation, and reduction of area of metal products. It applies to metallic materials in any form including: sheet, plate, wire, rod, bar, pipe, and tube. For each of these specimen types, the standard defines suitable geometries and dimensions, requiring specific gripping solutions that are critical to performing a successful test. The most common types of specimens are rectangular and round.

For testing rectangular type specimens we use a variety of mechanical wedge action grips, including manual, pneumatic, and hydraulic with flat serrated faces. In the case of round specimens, we suggest using vee-serrated or threaded faces, dependent upon the geometry of the specimen ends. To test fine wires we typically use pneumatic cord and yarn grips that appropriately distribute the load in a long section of the wire to avoid brakes in the clamping zone. Improper preparation of specimens is often the reason for unsatisfactory test results. To ensure accurate and precise test results, specimens should be machined carefully.

To guarantee accurate results, our series of Universal Testing Machines meet or exceed the accuracy specifications requested by ASTM E8. Bluehill^® Software provides standard functions to perform tensile tests easily and accurately. For more complex test requirements that require changing the rate at different points or for specific stressing or straining rates, we recommend using the Bluehill 3 Metals Application Module. This module also allows us to calculate results such as yield point elongation, and upper and lower yield as directed by ASTM E8.

We offer a range of extensometry solutions for tensile testing of metals. Our extensometers meet or exceed the accuracy classifications by ASTM E8. When performing strain measurements, such as the strain corresponding to the yield strength, we typically recommend our automatic extensometer, the AutoX750. Using an automatic extensometer helps reduce operator influence on the test while also ensuring accurate data. Other extensometer options that can be used to meet E8 are the 2630 series of axial clip-on extensometers. Non-contacting extensometers, such as the Automatic Video Extensometer 2 (AVE 2), allow us to determine the elongation at fracture without exposing the equipment to damage due to the energy released.

The topics we included here are some of the main points of E8; however, due to the complexities and enormity of ASTM E8, we recommend that you review the standard to fully understand its requirements.