ASTM E8/E8M Standard Test Methods for Tension Testing of Metallic Materials

Get Certified ASTM E8/E8M Testing for Reliable Metallic Material Data

ASTM E8/E8M states that the methods are satisfactory for acceptance testing of commercial shipments, and the trade has used them extensively for that purpose. A report from an accredited laboratory, produced on a testing machine verified to ASTM E4 and with an extensometer classified to ASTM E83, gives buyers and producers tensile data they can check. The report documents the specimen type, gauge length, units, and control method, so buyers can repeat and compare the results. It also supports material qualification, quality control, and product specifications.

The scope of ASTM E8/E8M includes

• Material type: Metallic materials in any form
• Test condition: Room temperature, 10 °C to 38 °C unless otherwise specified
• Properties measured: Yield strength, yield point elongation, tensile strength, elongation, and reduction of area
• Specimen types: Plate-type, sheet-type, round, full cross-section wire, rod, and bar, and pipe and tube
• Gauge length of round specimens: 4D for E8 and 5D for E8M
• Units: SI and inch-pound values are stated separately, and combining them may result in non-conformance
• Related documents: ASTM A370 for steel products, ASTM B557 and B557M for aluminum and magnesium alloys, and ASTM E345 for metallic foil
• Use: Comparison of materials, alloy development, quality control, design, and acceptance testing

What are the uses of ASTM E8/E8M Testing?

ASTM E8/E8M helps producers, buyers, and laboratories measure the strength and ductility of metals under uniaxial tensile stress. Many product specifications refer to it, including standards for copper alloy products, tantalum, and cobalt alloy tubing for surgical implants, and ASTM F606/F606M refers to it for machined fastener specimens. This standard:

•  Supports quality control of production lots.
• Supports acceptance testing of commercial shipments.
•  Helps alloy developers compare compositions and heat treatments.
•  Provides input to design, under the cautions the standard gives.
•  Gives standards writers a method to cite in product specifications for metals.
• Gives testing laboratories a consistent way to report tensile data.

What materials can be tested under ASTM E8/E8M?

ASTM E8/E8M applies to metallic materials in any form. The specimen type depends on the product and its thickness. Sheet-type specimens suit material from 0.13 mm to 5 mm thick, and either sheet-type or plate-type specimens suit material from 5 mm to 12.5 mm. Material from 12.5 mm to 19 mm can also use the largest practical round specimen, and material 19 mm or thicker uses the plate-type or round specimen. Wire, rod, and bar are tested full size where practicable, and small tubes are usually tested as full-size tubular sections with plugs in the ends. ASTM E345 applies to metallic foil.

Why is ASTM E8/E8M Important?

Tension tests provide information on a material’s strength and ductility under uniaxial tensile stress, and the standard methods let different laboratories get comparable results. The standard also warns that a specimen machined from one part of a product may not fully represent the whole product or its behavior in service. Test conditions matter. For a standard 12.5 mm round specimen, the stress rises by 1.5 percentage points for each 0.025 mm of load eccentricity, so alignment is part of the method.

ASTM E8/E8M Testing Process and Data Collection

The technician measures the specimen and marks the gauge length. The technician mounts the specimen in the grips, checks alignment, and attaches the extensometer. The machine loads the specimen at the chosen control method until it fractures, and the system records force and strain. Tensile strength is the maximum force divided by the original cross-sectional area. Yield strength is the engineering stress at which plastic elongation begins, and it may be defined by an offset from the linear stress-strain line, a specified total extension, or the maximum or minimum stress during discontinuous yielding.

Common Challenges and Troubleshooting

Misalignment is the most common problem. It adds bending stress, and the effect grows as the specimen gets smaller. Poor machining can leave cold work, notches, or burrs that cause fracture outside the gauge length. If a rectangular specimen fractures within two widths of the grip edge, the properties may not represent the material. Elongation values are comparable only when the gauge length stays at 4D for E8 or 5D for E8M within tolerance. Specimens smaller than 6 mm in diameter are restricted to cases where the material is too small for a larger one or all parties agree. Mixing SI and inch-pound values can also make a test non-conforming.

• Laboratory reports yield strength based on the definition used (an offset, a specified total extension, or the maximum or minimum stress during discontinuous yielding), along with yield-point elongation, tensile strength, elongation, and reduction of area. Elongation and reduction of area appear as percentages.
• Technicians record the specimen type, gauge length, units, and test temperature, because elongation values depend on the gauge length ratio, so others can repeat and review the test.
• Analysts calculate tensile strength from the maximum force and the original cross-sectional area, and report yield point elongation as the strain between the first point of zero slope and the transition to uniform strain hardening. Yield point elongation is 0 % if the curve has no such point.
• The engineer compares each result with the minimum in the product specification and recognizes that a specimen machined from one part of a product may not represent the whole product.
• Manufacturers or purchasers accept a result that meets the minimum without a retest, and discard and retest a result below the minimum when the fracture occurred too near the grips.

Link to ASTM E8/E8M Standard