ASTM E8/E8M Test for Tension Testing of Metallic Materials Scope:

ASTM E8/E8M tension tests are used to determine the strength and ductility of metals under uniaxial tensile stresses. The data from these tests are useful in comparisons of materials, alloy development, quality control, and design. These tests are extensively used for acceptance testing of commercial shipments. 

Test Procedure:

In ASTM E8/E8M the test machine is warmed up to normal operating temperatures to minimize errors that may result from transient conditions. The specimen is weighed and its dimensions are measured. The gauge section of the specimen is marked with ink. The gauge section is the part of the specimen where elongation occurs. It is between the two gripping shoulders of the specimen. 

The testing machine grips the specimen and gradually extends it until it fractures. During this process, the elongation of the gauge section is recorded against the applied force. The data is manipulated so that it is not specific to the geometry of the test sample.

The strength and ductility of materials under uniaxial tensile pressures can be determined by tension tests. Under certain conditions, this data may be helpful for material comparisons, alloy development, quality control, and design. The strength and ductility qualities of the entire finished product or its in-service behavior in various conditions may not be completely represented by the results of tension testing of specimens machined to defined dimensions from selected sections of a part or material.

Video 01: Tensile testing and stress-strain diagram of metals

Specimen size:

Usually, tensile specimens have two shoulders and a gauge section between them. The shoulders are bigger so they can be easily gripped and the gauge section has a smaller cross-section so that deformation and failure can occur in this area. 

For round specimens, the gauge lengths should be 4D for ASTM E8 and 5D for ASTM E8M. The gauge length is the most significant difference between ASTM E8 and ASTM E8M test specimens. Test specimens made from powder metallurgy materials are exempt from this requirement. 

Data:

The following data is calculated in ASTM E8/E8M testing:

1. Tensile strength:

S_u = P_max  /A

S_u  = the tensile strength

P_max = the maximum load

2. Yield point: the stress beyond which a material becomes plastic,

 YP  = P_YP /A₀

 P_YP = load at the yield point. 

3. Percentage elongation: The extent to which the test specimen has stretched at failure,

Elongation = ɛ = (ΔL/L₀) x 100

 ΔL: Change in length

 L₀: Initial length

4. The percentage reduction of area (%RA): The amount the specimen has necked or reduced in diameter at the point of failure,

Conclusion:

ASTM E8/E8M tension tests are used to determine the strength and ductility of metals under uniaxial tensile stresses. The data from these tests are useful in comparisons of materials, alloy development, quality control, and design.