For material testing under environmental conditions like pressure, test medium and temperature, testing machines are extended with autoclave units in which controlled ambient conditions are set. The load is applied to the specimen placed inside the autoclave from the outside via rods. Thepressure of the testing environment is sealed by the autoclave system. The challenge of this setup is the correct measurement of the specimen force due to the frictional forces on the gasket. The most current problem in this field, on which we focus our work, is the precise determination of material properties under high-pressure hydrogen atmosphere.

At the Materials Testing Institute (MPA) University of Stuttgart, a new measurement principle was developed which solves the conflicting objectives of precise force measurement and reusability of strain gauges. This is achieved by applying the strain gauges on the inside of the load rod which transfers the force onto the specimen inside the autoclave. The newly developed measuring principle was integrated into an existing testing machine. The applicability of the measuring setup was validated in experimental tests under cyclic load and with the test environment of highly pressurized hydrogen. 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 gasket.

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