ASTM E 8 describes tension 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. Rectangular plate specimens have a reduced area section with a 1.5-inch width and a nominal thickness of 3/16 inch or more. Sheet rectangular specimens have a reduced area section of 1/2 inch and their thickness should not exceed 3/4 inch. Subsize specimens with a 1/4-inch width can be used for material thicknesses up to 1/4 inch. When the material has a thickness of a 1/2 inch or more, round specimens can also be used. The most common specimens have a 1/2-inch diameter and are typically used for cast and wrought metallic materials.
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. In order 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 E 8. 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 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 E 8.
We offer a range of extensometry solutions for tensile testing of metals. Our extensometers meet or exceed the accuracy classifications by ASTM E 83. When performing strain measurements, such as the strain corresponding to the yield strength, we typically recommend our 2630 series of axial clip-on extensometers. Non-contacting extensometers, such as the Automatic Video Extensometer (AVE), 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.