ASTM E1450 Test for Tension Testing of Structural Alloys in Liquid Helium

Scope:

ASTM E1450 covers a tensile test done in a cryostat, a device used to maintain low cryogenic temperatures. This test is used to measure yield strength, tensile strength, elongation, and reduction of area. Tension tests provide information on the strength and ductility of materials under uniaxial tensile stresses. This information is used for alloy development, comparison and selection of materials, and quality control.

Test Procedure:

In ASTM E1450, the main apparatus includes a tensile cryostat for applying tensile forces to the test specimens in cryogenic environments. The dimensions of the specimen are measured. The specimen is installed in the cryostat. To prevent icing, the apparatus is dried with an air jet or heat gun. 

Cryogens (such as liquid helium) are substances used to produce extremely low temperatures. Cryogens are stored in a vacuum flask called a cryogenic dewar. In this test, the dewar is positioned on the cryostat and the liquid helium is transferred into the cryostat. The specimen is submerged in the liquid helium until it reaches thermal equilibrium. 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

Video 01: Superfluid helium

Specimen size:

In ASTM E1450, the 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.

Data:

The following data is calculated in ASTM E1450:

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,

5. Discontinuous Yielding Stress: