ASTM E8 is one of two major metals tension testing methods used worldwide 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 E8 specimens are rectangular and round. For testing rectangular type specimens, the standard gripping solution is a set of mechanical wedge action grips, (manual, pneumatic, or hydraulic) with flat serrated faces. In the case of round specimens, vee serrated or threaded faces can be used, depending on the geometry of the specimen ends. To test fine wires, pneumatic cord and yarn grips can be used. These grips distribute the load along an extended section of the wire to avoid specimen failure within the grips or at grip faces (“jaw breaks”). Specimen preparation is a critical part of metals testing, as improper preparation of specimens can yield unsatisfactory test results.
Bluehill® Universal Software provides standard functions to perform metals tensile tests easily and accurately, and also includes pre-made methods for the major metals standards, including ASTM E8. For more complex test requirements that require changing the rate at different points or for specific stressing or straining rates, the Bluehill Metals test type allows users to calculate results such as yield point elongation and upper and lower yield as directed by ASTM E8.
A range of extensometry solutions are offered for tensile testing of metals. When performing strain measurements such as the strain corresponding to the yield strength, Instron’s 2630 series of axial clip-on extensometers are the traditional solution. The non-contacting Advanced Video Extensometer 2 (AVE 2), allow users to determine the elongation at fracture without exposing the equipment to damage due to the energy released. This non-contacting solution is especially useful for thin foils, on which traditional contacting extensometers cannot be used. Instron’s AutoX750 automatic contacting extensometer is an advanced contacting extensometer that moves automatically and greatly improves test throughput.
The challenges of testing to this standard are:
- Strain control
- Gripping for varied specimen types
- Bluehill Universal contains an automatic loop control strain algorithm that allows for strain control without any setup or gain tuning required. This allows users to obtain excellent strain control on Instron systems with a number of different extensometers quickly and easily
- Instron has many gripping solutions for all types of metal specimens, from bar to dog bone to wire and foil specimens.
It is important to review ASTM E8 / E8M – 16a in order to fully understand the test setup, procedure, and results requirements.
For more information on ASTM E8 view our Definitive Guide to ASTM E8/E8M Tension Testing of Metals