ASTM E21 Test for Elevated Temperature Tension Tests of Metallic Materials

Scope:

ASTM E21 covers elevated temperature tension testing of metals. It is used to determine the ability of metals to withstand tensile forces at higher temperatures. The data can be used to indicate probable behavior under other simple stresses such as compression. However, the principal use of the elevated temperature tension test is to verify that the tested material is similar to the reference material.

Test Procedure:

In ASTM E21, the specimen has two shoulders and a reduced section between the shoulders. The gauge section is part of the reduced section. It is the part that elongates during the test. The cross-sectional area of the reduced section is measured. The gauge length is measured and marked. The specimen is cleaned with alcohol. Thermocouples are attached to the specimen to measure temperature. Extensometers are attached to the specimen to measure the extension of the gauge section during the test. The specimen is installed on the machine that has a furnace. At elevated temperatures, the specimen is slowly extended until it fractures. During this process, the elongation of the gauge section is recorded against the applied force.

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

Specimen size:

Usually, a tensile specimen has 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. 

• The size and shape of the test specimens used in ASTM E21 testing should be based primarily on the requirements necessary to obtain representative samples of the material being investigated.
• Specimens with circular cross-sections should have gripping ends that are threaded or shouldered. 
• The width at the ends of the reduced section should not be less than the width at the center of the reduced section. 

Data:

The following data is calculated in ASTM E21:

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 E21 covers elevated temperature tension testing of metals. It is used to determine the ability of metals to withstand tensile forces at higher temperatures.