Biaxial Permeation Test Device
Description:
Overview of Technology
A test for reusable composite cryogenic tanks, testing composite materials for gas permeation.
Background on Technology
Biaxial test frames generally apply biaxial loads in the form of a uni-axial load and torsional load. However, for certain applications like pressurized vessels, torsion is not desirable. There are few planar bi-axial test frames that are custom built to the requirements of the test, however, most of them are quite expensive (greater than $65000) and have a gage section that is too small (area is in the order of 100cm squared). Certification and flightworthiness tests rely on large structural and coupon level testing. A small gage area is often not enough to properly translate the mechanical behavior of a large structure, especially in the case of composite structures. Composite cryogenic tanks offer many benefits over their metal counterparts in terms of weight savings and specific strength. However, there is an added complexity of gas permeation through the microcracks in the tank wall that needs to be within an allowable range. The only way to properly understand if a composite reusable cryogenic tank has been properly designed, is to test for gas permeation under bi-axial thermo-mechanical stress. To achieve this, a relatively large specimen needs to be mechanically loaded biaxially in a cryogenic environment and pressurized on one side. A test frame in which the gas permeation can be measured through a large composite specimen while being under thermo mechanical stress, is therefore unique and not commercially available.
Description of Technology
Gas permeation testing coupled with thermo-mechanical stress is necessary for materials that are used in applications requiring lightweight pressure vessels such as reusable composite cryogenic tanks. A cost-effective planar bi-axial thermo-mechanical test frame with gas permeability measurement capabilities has been developed. The test frame has the capability to perform tests both in displacement and load control. Gas permeability measurements through specimens of any material can be measured using the apparatus, which is based on the volumetric method. This provides precise results for gases with small molecular diameters. Thermo-mechanical testing in combination with gas permeation testing of composite materials requires careful design of the fixture to provide the necessary sealing of the test article with minimal bending stresses. Large specimens can be tested under planar biaxial loads in a temperature chamber.
To address the gap in the market, MSU researchers have come up with a cost-effective and efficient design of a test frame that can apply planar biaxial loads to a large composite specimen under cryogenic temperatures and measure permeation of any purge gas through the composite specimen.
Benefits
- Cost effective
- Gas permeability capabilities
- Provides precise results
Applications
Current test frames that are capable of planar biaxial mechanical tests are expensive and often require test specimens that are small in size. Permeability measurements are difficult in such test frames as they aren’t designed to accommodate external apparatus to measure such properties.