Session: CS-08-01 Hydrogen Effects on Material Behavior for Structural Integrity Assessment (Joint MF-2)

Paper Number: 62072

Start Time: Wednesday, July 14, 2021, 09:00 AM

62072 - A Newly Developed Measuring Principle for Precise Measurement of Forces in Test Autoclaves 

Pressure, medium and temperature have a considerable influence on the mechanical properties of materials. If components are exposed to such environmental conditions during operation, the materials used must be tested under these conditions The most current problem in this field and on which we focus with our work is the development of a method to precise determine material properties under high pressure hydrogen atmosphere.

To determine the influence of pressure, medium and temperature on the strength of a material, testing machines are extended with autoclave units in which controlled ambient conditions are set. Load rods are used to transfer the forces of the testing machine from outside thought a seal to the specimen in the autoclave in order to keep the load cell and actuator outside the autoclave. Therefore, seals are placed on these load rods to separate the medium in the autoclave from the environment. A challenge here is the correct measurement of the actual force on the specimen. Due to the frictional forces on the seal, the measured forces are a superposition of actual specimen forces, friction forces and forces caused by the pressure acting on the font face of the load rod. Particular in the special case of hydrogen, the integration of a load cell inside the autoclave is not possible.

 

At the MPA University of Stuttgart a new test setup for the integration of the load cell in the autoclave was developed, which solves the conflict of objectives between a robust, durable design of the load cell and precise determination of the force on the specimen. For this purpose, the load rod is partly designed as a hollow cylinder and the strain gauges are applied to its inner side. It is important that the strain gages are mounted above the seal, so that they are permanently and exclusively in the flow of forces of the testing specimen. Above the strain gages, the load rod still has a full cross-section in order to maintain the seal against the autoclave. There is therefore no contact with the test medium.

 

The newly developed measuring setup was integrated into an existing test facility consisting of autoclave and testing machine at MPA University of Stuttgart. The strain gauges are arranged in such a way that both sample force and test pressure can be determined. The applicability of the measuring setup was validated in experimental tests under cyclic load and test medium hydrogen. In addition to the test pressure, it was also possible to determine the specimen force, which deviates from the test force specified via the testing machine.

With the help of the new test setup, it is possible to measure the actual specimen force, i.e. without the influence of the frictional force of the seal. This allows a more precise determination of the mechanical properties of a material and thus also an improved design of the components. This results in new potentials for the design of components.

Presenting Author: Alexandra Oßwald MPA University of Stuttgart

Authors:

Alexandra Oßwald MPA University of Stuttgart
Martin Werz MPA University of Stuttgart
Stefan Weihe MPA University of Stuttgart