Standard Test Methods for Tension Testing of Metallic Materials - PDF

 

ASTM E8 / E8M is the standard test method for tensile testing metallic materials to determine their mechanical properties, including yield strength, ultimate tensile strength, elongation, and reduction of area. This standard is widely used in metal production, quality control, materials research, and certification processes.

The “E8” designation refers to testing conducted in inch-pound (imperial) units, while “E8M” refers to testing in metric units. The testing method is largely identical in both cases, differing only in dimensions and units of measure.

Common Applications of ASTM E8

• Quality control in metal forming, rolling, casting, and forging industries

• Certification of raw materials for aerospace, automotive, and construction sectors

• Characterization of alloys and metals in research and development

• Baseline mechanical data generation for design engineers

What Does ASTM E8 Measure?

ASTM E8 provides a standardized method to determine:

1. Yield Strength (Offset or Extension Under Load)

2. Ultimate Tensile Strength

3. Modulus of Elasticity (optional)

4. Elongation (% over gauge length)

5. Reduction of Area (%)

These values provide insight into the material's behavior under uniaxial tensile loading.

Test Procedure Summary

The ASTM E8 test involves pulling a prepared metal specimen to failure while continuously recording load and extension. The stress-strain curve is used to calculate various properties.

Test Procedure Overview:

1. Prepare test specimens in accordance with standardized dimensions.

2. Install the specimen in the grips of a Universal Testing Machine (UTM).

3. Attach an extensometer over the gauge length.

4. Begin the test at the specified strain rate.

5. Record data continuously until failure.

6. Analyze results including yield strength, UTS, elongation, and reduction of area.

Specimen Types and Dimensions

ASTM E8 defines several standard specimen geometries, based on product form and cross-sectional area. These include:

1. Standard Round Specimens

Used for machined bar stock or forged metals.

• Gauge length: 2 inches (E8) or 50 mm (E8M)

• Diameter: Commonly 0.5 inch or 12.5 mm

2. Flat Specimens

For sheet, plate, or strip metals.

• Gauge width: 0.5 to 1.5 inches

• Thickness: As available, typically 1/8 inch or less

3. Subsize Specimens

Used when material is limited or non-standard sizes are needed.

4. Sheet Metal Dog-Bone Specimens

Used for thin sheets, prepared using laser, waterjet, or CNC machining.

Equipment Required for ASTM E8

To perform ASTM E8 accurately, you will need:

1. Universal Testing Machine (UTM)

• Capacity: Typically 50–300 kN, depending on specimen strength

• Load cell accuracy: ±1% or better

• Crosshead speed control for strain rate compliance

2. Grips

Proper grips are essential to avoid slippage or premature breakage:

a. Wedge Grips

• Most common choice for metal testing

• Self-tightening under load

• Compatible with flat and round specimens

b. Hydraulic Grips

• Offer high clamping force for high-strength alloys

• Useful for repeatable clamping of difficult materials

c. Threaded Grips

• Used for round specimens with threaded ends

3. Extensometers

An extensometer is required to measure elongation and yield properties.

• Clip-on extensometers for standard 2 in / 50 mm gauge lengths

• Automatic extensometers or video extensometers for hands-free operation

• Must comply with ASTM E83 Class B-2 or better for strain accuracy

Strain Rate and Crosshead Speed

Strain rate must be controlled during different parts of the test:

• Elastic region: Low strain rate (0.005 mm/mm/min recommended)

• Yield region: Maintain slow and steady rate to capture yield point

• Post-yield: Can increase speed up to 0.05 mm/mm/min until fracture

This rate control ensures repeatability and captures the yield point accurately, especially in metals with a yield plateau like mild steel.

Sample Preparation Guidelines

• Machining: Use lathe or CNC for round specimens; waterjet or laser cutting for flat dog-bones

• Surface finish: Smooth, free of burrs and stress risers

• Conditioning: Room temperature (typically 23°C ± 2°C) unless otherwise specified

• Marking: Gauge length should be clearly marked or identified for elongation measurements after fracture

Data Analysis and Reporting

After completing the test, the software or operator must extract the following values:

• Yield Strength (0.2% Offset or Extension Under Load Method)

• Ultimate Tensile Strength (UTS)

• Modulus of Elasticity (optional)

• Total Elongation (%)

• Reduction of Area (%)

• Stress-strain graph

• Photographic or visual fracture documentation (if required)

Ensure reporting includes specimen type, dimensions, test speed, and extensometer type.

Relevant Similar Standards

• ISO 6892-1 – International equivalent standard for tensile testing of metallic materials

• JIS Z2241 – Japanese standard for tensile testing of metals

• EN 10002-1 – European tensile test standard (now replaced by ISO 6892)

• ASTM A370 – For mechanical testing of steel products (includes tension, bend, impact tests)

• ASTM B557 – Tension testing of metallic materials specifically for aluminum and magnesium

• ASTM E111 – Determination of modulus of elasticity

Best Practices for Perfect ASTM E8 Testing

• Use calibrated machines with recent certification for force and extension.

• Always align specimens vertically in the centerline of the grips.

• Avoid slippage or bending by using the correct grips for your material and geometry.

• Pretest multiple specimens to dial in the proper strain rate and grip pressure.

• For brittle materials, use low-speed testing and high-resolution extensometers.

• Take photos of the fracture and measure elongation after break for full documentation.

Summary

ASTM E8 is the gold-standard method for tensile testing metals and alloys. It provides reliable mechanical property data used across manufacturing, R&D, and certification environments. By using the right grips, extensometers, machines, and strain rates—and following strict sample preparation protocols—you can ensure accurate, repeatable results that meet compliance requirements.